Journal of Morphology

Published by Wiley
Online ISSN: 1097-4687
Print ISSN: 0362-2525
The murine rodents are the most speciose subfamily of mammals. Here the morphology of the spermatozoon, as determined by scanning and transmission electron microscopy of representative species from four Eurasian clades, is described. Much interspecific variability in all components of the spermatozoon was found to occur, although most species have a bilaterally flattened sperm head with a single apical hook of variable length and orientation. Ultrastructural observations indicate that this apical hook invariably contains a nuclear projection as well as a large extension of the subacrosomal cytoskeleton, as a perforatorium rostrally, and a complex asymmetrical acrosomal extension. These spermatozoa also have relatively long tails that are attached to the lower concave surface of the sperm head. Uniquely, in species in the Apodemus clade, the apical hook is orientated caudally. In a few species a highly derived sperm head morphotype that does not contain an apical hook is present. These sperm heads vary in morphology from being globular in two species of Bandicota, to bilaterally flattened and paddle-shaped in Tokudaia and Micromys. In spermatozoa of the latter two genera the subacrosomal cytoskeleton, which is less extensive than in species with a hooked sperm head, forms an apical extension, but that is not the case in Bandicota. In all species where the sperm head lacks an apical hook the acrosome is more symmetrical. The sperm tail is much shorter in these species, with attachment to the head occurring on the ventral surface in Tokudaia and basal in Micromys and the two species of Bandicota. As the sperm head morphotype with a complex apical hook is present in all the major clades of murine rodents, it is likely to be a plesiomorphic character within each of these clades, with the nonhooked sperm heads, which vary greatly in structure between species of the different lineages, probably being independently derived. The ultrastructural organization of the sperm head of Bandicota, but not those of Micromys or Tokudaia, suggest divergence in some of the morphological events associated with sperm-egg interaction at the time of fertilization.
The cephalogenesis of chick embryos was studied at stages 3 through 11 inclusive. Ten embryos were examined at each stage. Particular attention was paid to the time of appearance of the prechordal plate mesoderm and cephalic notochord. It was found that the presumptive neural ectoderm begins to differentiate to form medullary plate as soon as it becomes associated with the chordamesoderm. Histological studies revealed the similarity of the notochord underlying the presumptive forebrain and midbrain regions, and the differences between this notochord and that associated with the hindbrain. These differences included the notochord histology and time of separation of the notochord from entoderm and neural ectoderm.
Rabbits are unique among mammals in that their ears can regenerate tissues from the margins of full thickness holes which grow in and completely fill the opening in about two months. The circular blastema that forms around the edges of the hole differentiates a new sheet of cartilage as it regenerates in a centripetal direction. Similar holes in other mammals fail to regenerate and form scar tissue instead of a blastema. Histological studies of the healing around the edges of rabbit ear holes reveal that during the second week, when the epidermis is completing its migration across the wound from the opposite sides of the ear, conspicuous tongues of epidermal cells grow down into the underlying tissues at the edges of the wound. These epidermal downgrowths are situated between the original intact dermis of the skin and the more central tissues which give rise to the blastema. Such downgrowths are of a transient nature, and are no longer found once the blastema rounds up toward the end of the second week. Since they are not found in the healing of similar wounds in rabbit ears prevented from regenerating by prior removal of their cartilaginous sheets, nor in the naturally nonregenerating ears of sheep and dogs, it is considered that these downgrowths of healing epidermis may play a role in the unusual regenerative response of ear tissues in the rabbit.
Three categories of dietary adaptation are recognized—faunivory, frugivory, and folivory—according to the distinctive structural and biochemical features of animal matter, fruit, and leaves respectively, and the predominance of only one in the diets of most species. Mammals subsisting mainly on animal matter have a simple stomach and colon and a long small intestine, whereas folivorous species have a complex stomach and/or an enlarged caecum and colon; mammals eating mostly fruit have an intermediate morphology, according to the nature of the fruit and their tendency to supplement this diet with either animal matter or leaves. The frugivorous group are mostly primates: 50 of the 78 mammalian species, and 117 of the 180 individuals included in this analysis are primates. Coefficients of gut differentiation, the ratio of stomach and large intestine to small intestine (by area, weight, and volume), are low in faunivores and high in folivores; the continuous spread of coefficients reflects the different degrees of adaptation to these two dietary extremes. Interspecific comparisons are developed by allowing for allometric factors. In faunivores, in which fermentation is minimal, the volume of stomach and large intestine is related to actual body size, whereas these chambers are more voluminous in larger frugivores and mid-gut fermenting folivores; fore-gut fermenters show a marked decrease in capacity with increasing body size. Surface areas for absorption are related to metabolic body size, directly so in frugivores; area for absorption is relatively less in larger faunivores and more in larger folivores, especially those with large stomachs. Indices of gut specialization are derived from these regressions by nonlinear transformation, with references to the main functional features of capacity for fermentation and surface area for absorption. These are directly comparable with the dietary index, derived from quantitative feeding data displayed on a three-dimensional graph, with all species within a crescentic path from 100% faunivory through 557ndash;80% frugivory to 100% folivory, perhaps illustrating, at least for primates, the evolutionary path from primitive insectivorous forms through three major ecological grades.
Juvenile 37 days after hatching. In toto staining with alizarin red. A small and flat tubercle with many digits.
The structure of the bony tubercles of the turbot, Scophthalmus maximus (L., 1758), was examined using ground sections, microradiography, SEM, and TEM. The tubercles are small, isolated, mineralized conical plates randomly distributed in the eyed side of the body. They are composed of three layers: the outer limiting layer, the external layer, and the basal plate, which make up the thin and flat elasmoid scales of Teleostei. The main difference between regular elasmoid scales and bony tubercles lies in the organization and the growth of the basal plate. Indeed, the conical shape of the tubercle is the result of a prominent thickening of the central part of the basal plate where the collagen matrix is organized in a complicated three-dimensional network. Densely packed thick collagen fibrils form superimposed plies organized in a plywood-like structure that resembles that of the elasmoid scales but it is criss-crossed by numerous vertical sheets of thin collagen fibrils. The tubercles originate from thin and flat plates located in the skin of larvae and juveniles, whose structure is that of regular-developing elasmoid scales. Thus, the tubercles of Scophthalmus maximus could be considered as modified elasmoid scales rather than bony structures. They might be the result of specific arrangements related to the general trend of reduction of the dermal skeleton in the teleostean lineage.
Caprimulgus europaeus. TEM. A: A further isodiametric spermatid sectioned longitudinally through the axoneme, confirming the short condition of the distal centriole compared with that in Galloanserae. Mitochondria are still scattered in the cytoplasm around the uncondensed nucleus. B: Detail of the same spermatid. Satellite rays are seen at the base of the distal centriole. The base of the flagellum is indented into the spermatid to form the transient cytoplasmic canal. As indicated by the arrow, there is no definite annulus. At this stage the central singlets of the axoneme do not penetrate the lumen of the distal centriole. C: Transverse section (TS) of the nucleus, with condensing chromatin, of the elongating spermatid. Longitudinal microtubules of the manchette surround the nuclear membrane but no circularly running microtubules are present. D: TS of the midpiece of an advanced elongating spermatid. Six mitochondria have assembled around the proximal axoneme to form the midpiece, within which the axonemal doublets are accompanied by dense fibers. Dense structures of unknown nature accompany the central singlets of the axoneme at this level. Microtubules of the manchette are still present. as, amorphous sheath; ax, axoneme; cc, cytoplasmic canal; cs, central dense structures; d, doublets of the axoneme; dc, distal centriole; m, mitochondrion; mt, longitudinal microtubules of the manchette; n, nucleus; nm, nuclear membrane; pc, proximal centriole; pp, principal piece; sr, satellite ray.
Caprimulgus europaeus . TEM. Elongating spermatids showing the form of the developing acrosome. A: Longitudinal section (LS) of the acrosome vesicle and adja- cent elongating nucleus. At this stage the acrosome vesicle has a simple, cowl-like shape. B: LS of acrosomes of three elongating spermatids. A subacrosomal space has developed and (lower acrosome) subacrosomal material is forming a putative perforatorium that projects into the tip of the nucleus. C: The perforatorium lies in an endonuclear canal. D: The dense perforatorium projects into the subacrosomal space. E: LS of a more mature acrosome. The perforatorium lies in the endonuclear canal and extends somewhat amorphously into the subacrosomal space. The acrosome vesicle is as- suming a conical form. F: Transverse section of an advanced acrosome showing the base of the acrosome vesicle enclosing the tip of the nucleus with its endonuclear canal and perforatorium. av, acrosome vesicle; ec, endonuclear canal; mt, microtubules of manchette; n, nucleus; p, putative perforatorium; sa, subacrosomal space. 
Caprimulgus europaeus. TEM. A: Transverse sections (TS) of midpieces and nuclei of advanced elongating spermatids. Four to six mitochondria surround the proximal axoneme as the midpiece. Dense fibers associated with the axonemal doublets are small in these sections. The chromatin of the nuclei has become clumped as condensation proceeds. Longitudinal but no circularly running cytoplasmic microtubules are present. B: TS of elongating spermatids. Left through the transient cytoplasmic canal and contained axoneme. Center right: TS through a developing midpiece that has assembled only four mitochondria at this level. C: Longitudinal section (LS) of an elongating spermatid, showing proximal and distal centrioles and the axoneme surrounded basally by the transient cytoplasmic canal. Mitochondria are beginning to assemble to form the midpiece. The central axonemal singlets have penetrated the distal centriole. D: LS of nucleus that is fully condensed but is still accompanied by the manchette. E: TS of axoneme with weakly developed amorphous sheath. ax, axoneme; cc, cytoplasmic canal; cs, central singlets of axoneme; dc, distal centriole; m, mitochondrion; mp, midpiece; mt, microtubules of manchette; n, nucleus; ps, proximal centriole.
The sperm of Caprimulgus europaeus is typical of other nonpasserines in many respects. Features shared with Paleognathae and Galloanserae are the conical acrosome, shorter than the nucleus; the presence of a perforatorium and endonuclear canal; the presence of a proximal as well as distal centriole; the elongate midpiece with mitochondria grouped around a central axis (here maximally six mitochondria in approximately 10 tiers); and the presence of a fibrous or amorphous sheath around the principal piece of the axoneme. A major (apomorphic) difference from paleognaths and galloanserans is the short distal centriole, the midpiece being penetrated for most of its length by the axoneme and for only a very short proximal portion by the centriole. Nonpasserines differ from paleognaths in that the latter have a transversely ribbed fibrous sheath, whereas in nonpasserines it is amorphous, as in Caprimulgus, or absent. The absence of an annulus is an apomorphic feature of Caprimulgus, apodiform, psittaciform, gruiform, and passerine sperm, homoplastic in at least some of these. In contrast to passerines, in Caprimulgus the cytoplasmic microtubules in the spermatid are restricted to a transient longitudinal manchette. The structure of the spermatid and spermatozoon is consistent with placement of the Caprimulgidae near the Psittacidae, but is less supportive of close proximity to the Apodidae, from DNA-DNA hybridization and some other analyses.
The description of the superficial veins of the face and neck was based upon the dissection of 28 male and female adult tufted or brown capuchin monkeys (Cebus apella), captured in southern Goiás, Brazil.Although the venous arrangement of these areas is basically the same in all primates, some characteristic differences were noted: 1. the anterior jugular and common facial veins were absent; 2. most specimens had a venous hyoid arch, and a connecting vessel between the external jugular and subclavian veins; 3. the inferior petrosal sinus drains into the external jugular v. through the postglenoid foramen; 4. the facial, lingual and cephalic veins open into the external jugular vein; 5. both the internal and external jugular veins have about the same diameter; 6. the vascular pattern appears to be quite stable; anatomical variations appear to be few and unimportant.
Pelagic egg development in red drum, Sciaenops ocellatus, is described using tiered staging. Based on mitosis and meiosis, there are five periods: Mitosis of Oogonia, Active Meiosis I, Arrested Meiosis I, Active Meiosis II, and Arrested Meiosis II. The Periods are divided into six stages: Mitotic Division of Oogonia, Chromatin Nucleolus, Primary Growth, Secondary Growth, Oocyte Maturation and Ovulation. The Chromatin Nucleolus Stage is divided into four steps: Leptotene, Zygotene, Pachytene, and Early Diplotene. Oocytes in the last step possess one nucleolus, dispersed chromatin with forming lampbrush chromosomes and lack basophilic ooplasm. The Primary Growth Stage, characterized by basophilic ooplasm and absence of yolk in oocytes, is divided into five steps: One-Nucleolus, Multiple Nucleoli, Perinucleolar, Oil Droplets, and Cortical Alveolar. During primary growth, the Balbiani body develops from nuage, enlarges and disperses throughout the ooplasm as both endoplasmic reticulum and Golgi develop within it. Secondary growth or vitellogenesis has three steps: Early Secondary Growth, Late Secondary Growth and Full-Grown. The Oocyte Maturation Stage, including ooplasmic and germinal vesicle maturation, has four steps: Eccentric Germinal Vesicle, Germinal Vesicle Migration, Germinal Vesicle Breakdown and Resumption of Meiosis when complete yolk hydration occurs. The period is Arrested Meiosis II. When folliculogenesis is completed, the ovarian follicle, an oocyte and encompassing follicle cells, is surrounded by a basement membrane and developing theca, all forming a follicle complex. After ovulation, a newly defined postovulatory follicle complex remains attached to the germinal epithelium. It is composed of a basement membrane that separates the postovulatory follicle from the postovulatory theca. Arrested Meiosis I encompasses primary and secondary growth (vitellogenesis) and includes most of oocyte maturation until the resumption of meiosis (Active Meiosis II). The last stage, Ovulation, is the emergence of the oocyte from the follicle when it becomes an egg or ovum.
This study provides the first evidence of pronounced temporary laryngeal descent in a bovid species. An elaborate acoustic display is prominent in male courtship behavior of polygynous Mongolian gazelle. During rut, rounding up of females is accompanied by continuous head-up barking by dominant males. Throughout the rut their evolutionarily enlarged larynx descends to a low mid-neck resting position. In the course of each bark the larynx is additionally retracted toward the sternum by 30% of the resting vocal tract length. A geometric model of active larynx movements was constructed by combining results of video documentation, dissection, skeletonization, and behavioral observation. The considerable distance between resting position and maximal laryngeal descent suggests a backward tilting of the hyoid apparatus and an extension of the thyrohyoid connection during the retraction phase. Return to the resting position is effected by strap muscles and by the elastic recoil of the pharynx and the thyrohyoid connection. An intrapharyngeal inflation of the peculiar palatinal pharyngeal pouch of adult males is inferred from a short-time expansion of the ventral neck region rostral to the laryngeal prominence. The neck of adult dominant males is accentuated by long gray guard hairs during the rut. The passive swinging of the heavy larynx of adult males during locomotion gives the impression of a handicap imposed on rutting males. Apparently, this disadvantage becomes outweighed by the profits for reproductive success.
The strongly modified mode of development of the small and brooding galeommatoid bivalve Lasaea adansonii (Gmelin, 1791) [syn. Lasaea rubra (Montagu, 1803)] has been studied by means of transmission and scanning electron microscopy and by fluorescent staining of the muscular system and of two neurotracers, FMRFamide and serotonin. In addition, two developmental stages were visualized using computer-aided 3D-reconstruction. All larval stages of L. adansonii lack ciliary rings. The apical organ appears invaginated: the base of the duct contacts the cerebral ganglia and opens on the preoral region. Larval protonephridia are lacking. The adult kidneys develop independently of the pericardial cavity and contain a protonephridial part that enables excretory function until the pericardium is formed. The larval muscular system is composed of smooth muscle fibers; striated fibers are lacking. Posteriorly and immediately below the ligament, a paired cell of unknown function is present that contains serotonin and FMRFamide. In summary, L. adansonii exhibits the direct mode of development. Only few truly larval structures (e.g., the modified apical organ) are elaborated.
The rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), is a salmoniform fish that spawns once per year. Ripe females that had ovulated naturally, and those induced to ovulate using salmon gonadotropin-releasing hormone, were studied to determine whether follicles were forming at the time of spawning and to describe the process of folliculogenesis. After ovulation, the ovaries of postspawned rainbow trout were examined histologically, using the periodic acid-Schiff procedure, to stain basement membranes that subtend the germinal epithelium and to interpret and define the activity of the germinal epithelium. After spawning, the ovary contained a few ripe oocytes that did not ovulate, numerous primary growth oocytes including oocytes with cortical alveoli, and postovulatory follicles. The germinal epithelium was active in postspawned rainbow trout, as determined by the presence of numerous cell nests, composed of oogonia, mitotic oogonia, early diplotene oocytes, and prefollicle cells. Cell nests were separated from the stroma by a basement membrane continuous with that subtending the germinal epithelium. Furthermore, follicles containing primary growth oocytes were connected to the germinal epithelium; the basement membrane surrounding the follicle joined that of the germinal epithelium. After ovulation, the basement membrane of the postovulatory follicle was continuous with that of the germinal epithelium. We observed consistent separation of the follicle, composed of an oocyte and surrounding follicle cells, from the ovarian stroma by a basement membrane. The follicle is derived from the germinal epithelium. As with the germinal epithelium, follicle cells derived from it never contact those of the connective tissue stroma. As with epithelia, they are always separated from connective tissue by a basement membrane.
The swamp eel, Synbranchus marmoratus, is a protogynous, diandric species. During sex reversal, the ovarian germinal epithelium, which forms follicles containing an oocyte and encompassing follicle cells during the female portion of the life cycle, produces numerous invaginations, or acini, into the ovarian stroma. Within the acini, the gonia that formerly produced oocytes become spermatogonia, enter meiosis, and produce sperm. The acini are bounded by the basement membrane of the germinal epithelium. Epithelial cells of the female germinal epithelium, which formerly became follicle (granulosa) cells, now become Sertoli cells in the developing testis. Subsequently, lobules and testicular ducts form. The swamp eel testis has a lobular germinal compartment in both primary and secondary males, although the germinal compartment in testes of secondary males resides within the former ovarian lamellae. The germinal compartment, supported by a basement membrane, is composed of Sertoli and germ cells that give rise to sperm. Histological and immunohistochemical techniques were used to describe the five reproductive classes that were observed to occur during the annual reproductive cycle: regressed, early maturation, mid-maturation, late maturation, and regression. These classes are differentiated by the presence of continuous or discontinuous germinal epithelia and by the types of germ cells present. Synbranchus marmoratus has a permanent germinal epithelium. Differences between the germinal compartment of the testes of primary and secondary males were not observed.
Knee joints of one adult and three juvenile African elephants were dissected. The specific features of the articular cartilage with particular reference to matrix components were studied by light and electron microscopy and immunohistochemistry. The elephant knee joint cartilage contains an unusually low concentration of proteoglycans resulting in rather eosinophilic staining properties of the matrix. The very thick collagen fibers of the cartilage possibly represent collagen I. Except for the different thickness of cartilage at the weight-bearing surfaces of femur (approximately 6.7 mm) and tibia (approximately 11.2 mm) in juvenile elephants, light and electron microscopy did not reveal distinct topographical differences in cartilage structure, perhaps because of the high congruency of the articulating surfaces and resulting uniform load distribution in the knee. The number of cell profiles per section area of both femoral (approximately 950 cell profiles/mm(2)) and tibial cartilage (approximately 898 cell profiles/mm(2)) was low, indicating excessive matrix production by the chondrocytes during cartilage development. These unique properties could be a result of the enormous compressive load resting on the elephant knee. Maintenance of the equilibrium between biological function and resistance to compression seems to be crucial in the elephant knee joint cartilage. Any disturbance that interferes with this equilibrium appears to lead to arthrotic alterations, as particularly seen in captive elephants.
The phylogenetic position of bryozoans has been disputed for decades, and molecular phylogenetic analyzes have not unequivocally clarified their position within the Bilateria. As probably the most basal bryozoans, Phylactolaemata is the most promising taxon for large-scale phylogenetic comparisons. These comparisons require extending the morphological and developmental data by investigating different phylactolaemate species to identify basal characters and resolve in-group phylogeny. Accordingly, we analyzed the bud development and the organogenesis of the freshwater bryozoan Cristatella mucedo, with special focus on the formation of the digestive tract and differentiation of the coelomic compartments. Most parts of the digestive tract are formed as an outpocketing at the future anal side growing towards the mouth area. The ganglion is formed by an invagination between the anlagen of the mouth and anus. The lophophoral arms develop as paired lateral protrusions into the lumen of the bud and are temporarily connected by a median, thin bridge. All coelomic compartments are confluent during their development and also in the adult. The epistome coelom develops by fusion of two peritoneal infolds between the gut loop and overgrows the ganglion medially. The coelomic ring canal on the oral side develops by two lateral ingrowths and supplies the oral tentacles. On the forked canal, supplying the innermost row of tentacles above the epistome, a bladder-shaped swelling, probably with excretory function, is present in some adults. It remains difficult to draw comparisons to other phyla because only few studies have dealt with budding of potentially related taxa in more detail. Nonetheless, our results show that comparative organogenesis can contribute to phylactolaemate systematics and, when more data are available, possibly to that of other bryozoan classes and bilaterian phyla.
A detailed topography of adrenergic innervation in invertebrates (lobster), low vertebrates (fish, amphibians, reptiles, birds), and nine species of mammals is presented. Flack and Hillarp's specific fluorescent histochemical method using freeze-dried material was used. Phylogenetically, adrenergic innervation appeared earlier under the ciliary epithelium and in the muscle than surrounding the vessels, and in all species many fibers were without any connection to the vessel walls. Adrenergic innervation was very rich in the dilator muscle extending toward the epithelium of the posterior chamber; a surprisingly rich network was found in the sphincter muscle and also in ciliary spaces of some species. Numerous fluorescent mast cells were visualized in the pecten of the bird eye and in the ciliary tissue of the sheep and cow.
The ultrastructure of the mature spermatozoon of the type genus of the Plagiorchiidae Plagiorchis elegans (Rudolphi, 1802), a parasite of the Golden hamster, Mesocricetus auratus is described. This study is the first ultrastructural study of the spermatozoon of a Plagiorchis, the second of a plagiorchiid species and only the third in the Plagiorchioidea. Previously data on spermatozoon ultrastructure existed only for the plagiorchiid Enodiotrema reductum and the omphalometrid Rubenstrema exasperatum. The mature spermatozoon of P. elegans exhibited the general pattern described in most digenean species, namely two axonemes of the 9 + "1" Trepaxonemata pattern, nucleus, mitochondria, external ornamentation of the plasma membrane, spine-like bodies, and glycogen granules. However, the rather typical expansion of the plasma membrane is not found in P. elegans. Another peculiarity of the spermatozoon of P. elegans is the presence of a structure called thin cytoplasm termination. Spermatozoon ultrastructure of P. elegans is compared with that of E. reductum and R. exasperatum. Spermatozoon of P. elegans conforms to the general pattern described in E. reductum. Thus, this study further expands our knowledge on the spermatozoon ultrastructure among the members of the Plagiorchioidea, one of the most phylogenetically derived groups of the digenea. J. Morphol., 2013. © 2013 Wiley Periodicals, Inc.
We address the chondrogenic formation of the limbs and the mesopodial ossification pattern of the Pleurodira Podocnemis expansa, to resolve the homology of these elements as well as the pattern of connection of the autopodial elements and the origin of the digital arch. Embryos and juveniles of P. expansa were cleared and stained for cartilage and bone. The fore- and hind-limbs were also studied histologically. We describe the development of the stylopodium and zeugopodium originating from a Y-shaped cartilaginous condensation, and the differentiation of the primary axis and the digital arch in the initial stages of limb development. The most pronounced changes were observed in the chondrogenic pattern and ossification of the mesopodium, although development of the digits is similar and we found no ontogenetic reduction such as that described for other Testudines. In this study, as in previous research involving several groups of reptilian sauropsids, we found an inconsistent pattern between the chondrogenic formation and mesopodial ossification of the limbs, indicating that these developmental events are dissociated. In summary, the chondrogenic and ossification sequences of these elements do not follow the same pattern. In addition, the differences found between P. expansa and other species to which it was compared clearly indicate that these events follow more than one pattern in Testudines.
The clouded leopard (Neofelis nebulosa) is an unusual medium-sized felid whose ecology in the wild is poorly known. Mainly famous for its large canines, it has often been an overlooked taxon in analyses of felid morphology and systematics or has proven aberrant and difficult to interpret. In this article I report on a number of unusual features in the clouded leopard skull hitherto considered characteristic of sabertooth felids exclusively, and, accordingly, universally believed to be absent in extant felids. The skull morphology of the clouded leopard sets it apart from other extant felids, and in a number of respects it approaches the morphology of primitive sabertooths. This indicates convergence of several characters in machairodontine felids and the clouded leopard, mainly as adaptations for attaining a large gape. This raises doubts about the characters hitherto considered as distinguishing sabertoothed from nonsabertoothed predators, and since no evidence at present suggests a different functional killing and feeding ecology in Neofelis, regardless of its unusual skull morphology, also whether primitive sabertoothed felids were functionally similar to advanced forms such as Homotherium, Megantereon, or Smilodon.
The study of the pharyngeal jaws in two geographically isolated Italian populations of Lebias fasciata indicated the presence of two phenotypes: the Adriatic phenotype with a large ceratobranchial V and upper and lower pharyngeal jaws bearing few large teeth and the Sicilian phenotype with a smaller ceratobranchial V and pharyngeal jaws with smaller and more numerous teeth. The morphological variations of pharyngeal jaws should be interpreted as a result of the geographical isolation of these two populations.
We examined the effect of temperature during the early development on the phenotypic plasticity of Danio rerio. The effect of temperature was examined during two different early developmental periods of 280°d (the product of days × temperature) each, 28-308°d or 280-560°d, by subjecting the experimental populations to three different water temperatures (22°C, 28°C, and 32°C). Before and after the end of the 280°d period of the different thermal exposure, all populations were cultured in standard temperature (28°C). Five to 10 months after exposure to the different thermal regimes, the body shape of the adults was analyzed by geometric morphometrics. In both ontogenetic windows and experimental repetitions, the results showed that developmental temperature and sex significantly affected the body shape of adult zebrafish. Thermally induced shape variation discriminated the fish that developed at 22°C from those developed at 28°C-32°C. In the early developmental period (DP1, 28-308°d postfertilization), dorsal, anal, and caudal fin structures differed between the animals that developed at 22°C and 28°C-32°C. In the later developmental period (DP2, 280-560°d postfertilization), caudal, anal, pectoral, and pelvic fins, as well as the gill cover and lower jaw, were affected when animals developed at different temperatures. These results show that thermal history during a short period of embryonic and larval life affects the body form of adult zebrafish with potentially functional consequences. Based on previous data on the effects of temperature on fish development, we suggest thermally induced muscle and bone remodelling as possible mechanism underlying the observed plasticity.
A-H. TEM of L. cuprina and L. eximia. A: Cross sections of the testis wall in L. eximia. In the strata, forming the testis wall, it is possible to see: an external layer with pigmented grains named peritoneal sheath (Ps); a layer of muscle (Ml) delimited by basement membrane (Bm), and follicular epithelium (Fe). B–H: L. cuprina. B: Cyst (Cy) showing spermatozoa. Observe the absence of membrane delimitation of cystic cell. C–H: Cross sections through testes, showing early spermatids. C,D: Acrosome (Ac) formation. C: Acrosomal vesicle (Av) is observed near to the Golgi complex (Gc). The chromatin of nucleus (N) appears dispersed. D: The acrosome (Ac) could be seen at the apex of the nucleus (N) in process of elongation. E–H: Chromatin condensation. The first aspect observed is the increase of aggregation of chromatin forming masses in some regions of nucleus (N); followed by the fibrous, lamellar, and highly compacted aspects, respectively. Accessory membranes (star) and microtubules (Mt).
TEM of early spermatids of L. cuprina (A,D–H) and L. eximia (B,C,I–K). A–C: In cross section of the tail region the fusion was observed of several mitochondria to form the nebenkern (Ne). D: The implantation of the axoneme (Ax) occurs in the nuclear region. Nucleus (N), accessory membranes (star), and microtubules (Mt). E–G: The nuclear, “overlap” and tail region in spermatid. The accessory membranes (star) and microtubules (Mt) are present in these regions. E: The feature of nuclear region shows the nucleus (N), the axoneme (Ax), and the beginning of two mitochondrial derivatives (Md). F: This is the “overlap” region, marked by the beginning of the centriolar adjunct (Ca). G: The tail region is marked by the disappearance of the nucleus and presence of the flagellar structures. H: In longitudinal section, it is possible to observe the nucleus (N) and the centriolar adjunct (Ca) in their posterior region. I–K: Tail structures. I: The morphologic aspect of the mitochondrial derivative (Md) suggests that it will divide into two, but it remains single. J–K: It is possible to observe only one mitochondrial derivative (Md), located between the nucleus (N) and the axoneme and in front of the axoneme (Ax), respectively. The paracrystalline material is observed (asterisk).
TEM of the nuclear, “overlap” and tail regions in the three species analyzed. A–F: Cross sections of spermatozoa of L. cuprina. A: Even in the nuclear region, it is possible to observe the complete axoneme (Ax) and the beginning of the symmetric mitochondrial derivatives (Md). B: The “overlap” region is marked by the appearance of the centriolar adjunct (Ca). In this region, the nucleus (N) and the tail structures can be observed. Axoneme (Ax) and mitochondrial derivatives (Md). C–F: Tail region. C: The region of the tail is marked by the end of the nucleus, the increase in the centriolar adjunct (Ca), and presence of the axoneme (Ax), and the mitochondrial derivatives (Md). D–F: The next regions are characterized by the disappearance of the centriolar adjunct, reduction in diameter and loss of one mitochondrial derivative (Md). G: Longitudinal section of nucleus and tail region in L. eximia. In this region, it is possible to observe the nucleus (N), the centriolar adjunct (Ca), and the axoneme (Ax). H–K: Cross sections of spermatozoa in L. eximia and L. peruviana. The material of L. peruviana was obtained from spermathecae. H: L. eximia. Even in the nuclear region, it is possible to observe the complete axoneme (Ax) and the beginning of only one mitochondrial derivative (Md). I: The “overlap” region of L. peruviana. J–K: Tail region in L. peruviana and L. eximia, respectively. L–Q: L. eximia. L: Longitudinal section of mitochondrial derivative (Md), showing the paracrystalline material (asterisk). M–Q: Features of the axoneme. M. See the intertubular material (arrow). The axoneme in all analyzed species is made up of nine accessory microtubules, nine doublets, and a central pair. N–Q: The accessory microtubules (arrow) possess 13 protofilaments, and in a final portion of flagellum, one can see the gradual disorganization of the axoneme (Ax).
Schematic representation of spermatozoa of (A) L. cuprina, (B) L. eximia, and L. peruviana , corresponding to the longitudinal and cross sections. (i) acrosome; (ii) acrosome and nucleus; (iii) nucleus; (iv) “peg” region; (v,v′) beginning of mitochondrial derivative; (vi,vi′) region of “overlap”; (vii,vii′) beginning the flagellar region; (viii) ending of the centriolar adjunct; (ix,x) endpiece of flagellum. Acrosome (ac), axoneme (ax), centriolar adjunct (ca), mitochondrial derivative (md), and nucleus (n).
Morphology of male internal reproductive organs, spermatozoa, and spermiogenesis of the blow-flies Lucilia cuprina, Lucilia eximia, and Lucilia peruviana is first described here, using light and transmission electron microscopy. Spermiogenesis follows the characteristics described for others insect species. The spermatozoa of L. cuprina are similar to those described for other Brachycera. However, in L. eximia and L. peruviana, some differences were found. In L. cuprina and L. eximia species, the spermatozoa are long and thin, measuring about 211 μm and 146 μm in length, of which the head region measures approximately 19 μm and 17 μm, respectively. A polymorphism was observed in L. cuprina and L. eximia spermatozoa. In all three species, the head includes a monolayered acrosome with electron-lucent material. The shape of the nucleus, in cross sections, varies from circular to oval with completely condensed chromatin. Implantation of the axoneme was observed in the middle region of the nucleus, known as the "peg" region. In the next region, the beginning of two mitochondrial derivatives of similar diameter and different lengths in L. cuprina and only one in L. eximia and L. peruviana was observed. In the overlap region, the following structures were observed: nucleus, centriolar adjunct, mitochondrial derivatives, and axoneme. The axoneme is of a conventional insectan type with a 9 + 9 + 2 microtubular arrangement. The male internal reproductive tract consists of testis, deferent ducts, a strongly developed seminal vesicle, accessory glands, and ejaculatory duct. These features are consistent with the structural diversity of the dipteran reproductive tract and spermatozoa, comprising an essential tool for understanding the complex variations found in the Diptera.
Sea anemones have a structurally simple nervous system that controls behaviors like feeding, locomotion, aggression, and defense. Specific chemical and tactile stimuli are transduced by ectodermal sensory cells and transmitted via a neural network to cnidocytes and epithelio-muscular cells, but the nature of the neurotransmitters operating in these processes is still under discussion. Previous studies demonstrated an important role of peptidergic transmission in cnidarians, but during the last decade the contribution of conventional neurotransmitters became increasingly evident. Here, we used immunohistochemistry on light and electron microscopical preparations to investigate the localization of glutamate and GABA in tentacle cross-sections of the sea anemone Phymactis papillosa. Our results demonstrate strong glutamate immunoreactivity in the nerve plexus, while GABA labeling was most prominent in the underlying epithelio-muscular layer. Immunoreactivity for both molecules was also found in glandular epithelial cells, and putative sensory cells were GABA positive. Under electron microscopy, both glutamate and GABA immunogold labeling was found in putative neural processes within the neural plexus. These data support a function of glutamate and GABA as signaling molecules in the nervous system of sea anemones.
Geophis belongs to the goo-eating dipsadine assemblage of snakes that are known to feed exclusively on earthworms, snails, and slugs. Although the unusual feeding strategies of the goo-eating dipsadines are well known (but poorly documented), little attention has been paid to their internal anatomy. Here, we describe a new and noteworthy morphological and histochemical condition of the infralabial glands in three species of Geophis (G. brachycephalus, G. nasalis and G. semidoliatus), all earthworm feeders. Their infralabial glands are constituted of two distinct parts: an anterolateral portion composed of mucous and seromucous cells that stretches from the tip of the dentary to the corner of the mouth, and a tubular posteromedial portion that is exclusively seromucous. The anterolateral portion receives fibers of the levator anguli oris muscle that attaches on its posterodorsal extremity while the posteromedial portion extends posteriorly to the corner of the mouth where it receives fibers of the adductor mandibulae externus medialis muscle. Furthermore, the posteromedial portion of the infralabial gland is constituted by large acini filled with secretion that is periodic acid-Schiff positive. These acini release their secretion directly into a large lumen located in the middle of the glandular portion. In the three species examined, the supralabial glands show a traditional configuration, being constituted of mucous and seromucous cells and retaining an enlarged part in its caudal region that resembles a Duvernoy's gland. The presence in Geophis of an expanded lumen in part of the infralabial gland that is compressed by an adjacent muscle suggests a more specialized role for the secretion produced by these glands that may not be related to envenomation but rather to prey transport and mucus control. J. Morphol., 2013. © 2013 Wiley Periodicals, Inc.
Demersal fishes have complex life cycles that involve an ontogenetic change in morphology, physiology, and behavior, as their pelagic larval stages colonize benthic habitats. The developmental transition between larvae and juveniles leads to very complex processes of morphogenesis and differentiation. These processes primarily determine changes in external morphology, which is shaped by selective pressures to optimize performance for basic activities such as swimming, escape from predators, and feeding. Fishes have provided fertile grounds for ecomorphological investigations throughout ontogeny, as the role of changing morphology in inducing ontogenetic niche shifts is not always clear. In this framework, some studies have demonstrated that certain species undergo gradual changes, whereas other species experience threshold effects in their ecomorphological relationships during ontogeny. In this study, the intraspecific allometry of the dusky grouper was examined. Geometric morphometric tools were used to quantify shape changes through the development, and a modular approach was also applied to analyze the pattern of covariation between three distinct blocks (head, trunk, and tail). For this purpose, a two-block Partial Least Square was computed. This method reveals that the pattern of changes in the overall body shape is the result of the modularized changes of these blocks.
The morphology of the entoproct Barentsia gracilis (M. Sars, 1835), has been studied primarily by routine light microscopy techniques supplemented with observations by electron microscopy. In general, the B. gracilis adult is similar in structure to other members of the Pedicellinidae. Differences noted include: the presence of conspicuous fibers, probably collagenous, which appear to reinforce the stalk- calyx connection, the presence of a distinct glandular- appearing area (also present in the larva) of unknown function, and the presence of two rows of latero- frontal cilia on the tentacles. The first detailed morphology of an entoproct larva is also presented and the striking similarity to the adult noted. Due to the confused state of Barentsia systematics, it was found that B. gracilis, B. geniculata, and B. benedeni may very well be the same animal. This is due to the great variability, apparently due to ecological factors, found in the key taxonomic characters such as stalk morphology. The feeding behavior of the adult is described and the larval feeding and rejection mechanism is reported for the first time. The larva, while still in the brood pouch, uses its ciliary girdle to remove food from the parent's food groove. The larval feeding current is generally similar to that of the adult, with modifications which are related to the lack of tentacles in the larva. The larva differs from the adult in having special ciliated rejection pathways for the removal of excess food particles.
This study describes the male reproductive cycle of Sibynomorphus mikanii from southeastern Brazil considering macroscopic and microscopic variables. Spermatogenesis occurs during spring-summer (September-December) and spermiogenesis or maturation occurs in summer (December-February). The length and width of the kidney, the tubular diameter, and the epithelium height of the sexual segment of the kidney (SSK) are larger in summer-autumn (December-May). Histochemical reaction of the SSK [periodic acid-Schiff (PAS) and bromophenol blue (BB)] shows stronger results during summer-autumn, indicating an increase in the secretory activity of the granules. Testicular regression is observed in autumn and early winter (March-June) when a peak in the width of the ductus deferens occurs. The distal ductus deferens as well as the ampulla ductus deferentis exhibit secretory activities with positive reaction for PAS and BB. These results suggest that this secretion may nourish the spermatozoa while they are being stored in the ductus deferens. The increase in the Leydig cell nuclear diameter in association with SSK hypertrophy and the presence of sperm in the female indicate that the mating season occurs in autumn when testes begin to decrease their activity. The peak activity of Leydig cells and SSK exhibits an associated pattern with the mating season. However, spermatogenesis is dissociated of the copulation characterizing a complex reproductive cycle. At the individual level, S. mikanii males present a continuous cyclical reproductive pattern in the testes and kidneys (SSK), whereas at the populational level the reproductive pattern may be classified as seasonal semisynchronous. © J. Morphol., 2012. © 2012 Wiley Periodicals, Inc.
The genitalia of the female folding-trapdoor spider Antrodiaetus unicolor are characterized by two pairs of spermathecae that are arranged in a single row and connected to the roof of the bursa copulatrix. Each single spermatheca is divided into three main parts: stalk, bowl, and bulb, which are surrounded by the spermathecal gland. The epithelium of the spermathecal gland is underlain by a muscle meshwork and consists of different types of cells partly belonging to glandular cell units (Class 3 gland cells) that extend into pores in the cuticle of the stalk and bowl. Interestingly, the bulb lacks glandular pores and is characterized by a weakly sclerotized cuticle. This peculiarly structured bulb probably plays an important role in the discharge of the sperm mass. It is suggested that by contraction of the muscle layer the sperm mass may be squeezed out, when the bulb invaginates and expands into the spermathecal lumen, pushing the sperm to the uterus lumen. Each glandular unit consists of usually one or two central secretory cells that are for the most part surrounded by a connecting cell that again is surrounded by a canal cell. The canal cell, finally, is separated from the other epithelial cells (intercalary cells) located between the glandular units by several thin sheath cells that form the outer enveloping layer of the unit. The secretions are released through a cuticular duct that originates proximally between the apical part of the connecting cell and the apical microvilli of the secretory cells and runs into a pore of the spermathecal cuticle. The glandular products of the Class 3 gland cells likely contribute to the conditions allowing long-term storage of the spermatozoa in this species. Details regarding the ovary, the uterus internus, and the uterus externus are reported. Most of the secretion that composes the chorion of the egg is produced in the ovary. Glandular cell units observed in the uterus externus differ structurally from those in the spermathecae and likely play a different role. Finally, we briefly discuss our results on the female genitalia of A. unicolor in the light of knowledge about the reproductive biology of spiders.
The major organ systems of Goniodoris castanea were investigated by histological means, with an emphasis on those structures that are difficult to see by dissection. The species is characterized by some peculiar features that are unique or seldom within the Nudibranchia, such as the complete absence of specialized vacuolated cells, the presence of globular salivary glands, the presence of cuticular structures in the proximal intestine, a muscular sphincter around the distal vaginal duct, and the position of the blood gland closer to the pericardium than to the nervous system. Some of these characters are discussed in a phylogenetic context, although a thorough phylogenetic analysis is preliminary, due to lack of knowledge of probably related species.
The laryngeal apparatus of Caperea marginata is described for the first time and proves to be significantly different from that of any mysticete previously described. This difference is especially noticeable in the position of the laryngeal sac, which is separate from the tracheal rings and lies to the right of the animal. Massive ontogenetic development of the sac in adult males is demonstrated, far greater than that seen in most other mysticetes. Histological analysis of the laryngeal sac shows the walls to be very muscular, abundantly innervated, and vascularized, indicating an active organ. Coiled blood vessels and nerves support the hypothesis that the sac undergoes extensive expansion and contraction. A possible association with the unique thoracic development of the species is suggested. The roles of the laryngeal sac and arytenoid cartilages in mysticete sound production are also discussed.
Approximately 130 individuals of Acanthobdella peledina and 100 individuals of Paracanthobdella livanowi were studied. Morphometric measurements were taken to explore the body form. The digestive and the reproductive systems of leech-like annelids were analyzed for the first time in such a high number of specimens. Observation of A. peledina and P. livanowi revealed crucial differences in the reproductive system of the analyzed taxa, mostly regarding variation in the shape of the testisacs and the length of the ovisacs. The results of a digestive system analysis suggest that blood-sucking parasites of the order Acanthobdellida may also lead a predatory lifestyle. The presented findings support the taxonomic division of the order Acanthobdellida into the families Acanthobdellidae and Paracanthobdellidae. Multiple similarities between Acanthobdellida and Hirudinida were also discussed. J. Morphol., 2013. © 2013 Wiley Periodicals, Inc.
Phenotypic variation is important for evolutionary processes because it can allow local adaptation, promote genetic segregation, and ultimately give rise to speciation. Lacustrine systems provide a unique opportunity to study the mechanisms by which sister species can co-occur by means of ecological segregation. The fish genus Astyanax is characterized by high levels of phenotypic variability, providing an excellent model for the study of local specialization. Here, we analyze the morphological specializations through geometric morphometrics of two sympatric species described as different genera: Bramocharax caballeroi endemic to Lake Catemaco, and the widely distributed Astyanax aeneus. Additionally, we assess the correlation between phenotypic and genetic structure, and the phylogenetic signal of morphological variation. We examined body size and shape variation in 196 individuals and analyzed mitochondrial cytochrome b sequences in 298 individuals. Our results confirm the striking morphological divergence among the sympatric characids. Differences between them were mainly found in the body depth and profile and orientation of the head, where B. caballeroi in contrast with the A. aeneus, presented a fusiform body and an upward mouth. Moreover, different growth trajectories were observed among morphotypes, suggesting that a heterochronic process could be involved in the diversification of our study system. Morphological differences did not correspond with the molecular differentiation, suggesting high levels of homoplasy among the lineages of B. caballeroi morphs. J. Morphol., 2014. © 2014 Wiley Periodicals, Inc.
The results of an ultrastructural investigation of the gastric glands of the ruin lizard are reported. In this reptile the stomach can be divided into a larger fundus and a smaller pars pilorica. Fundic glands are characterized by three main kinds of cells: mucous, endocrine, and oxynticopeptic; the latter were not observed in the pyloric glands. The morphological features of the oxynticopeptic cells change from the proximal to the distal region of the fundic mucosa. In the proximal region, numerous electron-dense secretory granules, a well-developed granular endoplasmic reticulum, an evident Golgi complex, and a reduced system of smooth-surfaced vesicles and tubules in the apical cytoplasm characterize these cells. In the distal fundic region, oxynticopeptic cells possessed numerous mitochondria and a well-developed smooth-surfaced endoplasmic reticulum, but secretory granules were rare. These data suggest the existence of a gradient in the production of proteolytic enzymes, and perhaps also of hydrochloric acid, along the oral-aboral axis of the stomach. The results are discussed with regard to the evolution of the gastric glands and of the digestive mechanism in vertebrates.
The external morphology and internal structure of the male sexual tube of the hermit crab Micropagurus acantholepis, a member of the family Paguridae from Australian waters, is described in detail using histological thick sectioning and scanning and transmission electron microscopy techniques. This is the first in-depth study of a sexual tube in the Paguroidea, a group where a remarkable number of genera (55.9% in the family Paguridae) with species having these intriguing sexual structures are known. In M. acantholepis a sexual tube is present on the left side, whereas only a gonopore is present on the right side. The tube is used for the delivery of spermatophores to the female and consists of a sheath of cuticular origin surrounding an internal, functional extension of the posterior vas deferens. Pedunculate spermatophores were observed within the lumen and partially extruding from the terminal opening of the tube in preserved specimens. The tube protrudes from the left coxa of the fifth pereopod as an elongate 3-mm-long, hollow, coiled structure with a terminal opening. Exteriorly the tube consists of a conspicuous thick chitinous cuticular ridge throughout its length, and a thin chitinous cuticle with sparse, regularly arranged simple setae. Interior to the cuticle, the tube contains loose connective tissue, secretory cells, oblique muscle, circular muscle, and epithelial cells. The latter cells line a central lumen that runs the length of the sexual tube. The morphology, cellular composition, and function of the tube are discussed.
Three-dimensional reconstruction of right halve of the branchial basket of C. aeneus. (a) Stage 2, Dorsal view; (b) Stage 2, Ventral view; (c) Stage 3, Dorsal view; (d) Stage 4, Dorsal view; (e) Stage 5, Dorsal view; (f) Stage 6, Dorsal view. c-a, copula anterior; cb, ceratobranchial; c-p, copula posterior; eb, epibranchial; hb, hypobranchial; ipb, infrapharyngobranchial; ipb-a, infrapharyngobranchial anterior; ipb-p, infrapharyngobranchial posterior. Roman numerals indicate arch number./-symbol indicates fusion of elements.  
Three-dimensional reconstruction of the chondrocranium of C. aeneus (5.3 mm SL). (a) Dorsal view. (b) Ventral view of the neurocranium. (c) Right lateral view. apal, autopalatinum ; b-pob, preorbital base; c-eth, cartilago ethmoideum; ch, ceratohyale; cm-bc-a, commissura basicapsularis anterior; cmbc-p , commissura basicapsularis posterior; cm-bv, commissura basivestibularis; c-Meck, cartilago Meckeli; cm-lat, commissura lateralis; cm-spheth, commissura sphenoethmoidalis; cm-sphsep, commissura sphenoseptalis; c-ot, otic capsule; fn-bc-a, fenestra basicapsularis anterior; fn-hyp, fenestra hypophysea; fn-sph, fenestra sphenoidea; fr-car-i, foramen arteria carotis interna; fr-folf , foramen fila olfactoria; fr-on, foramen orbitonasalis; fr-IX, foramen nervus glossopharyngeus (fenestra basicapsularis posterior ); fr-X, foramen nervus vagus; hh, hypohyale; hs, hyosymplecticum ; ih, interhyale; lm-on, lamina orbitonasalis; lm-prc, lamina precerebralis; not, notochord; pns-ep, pons epiphysialis; q, quadratum; pr-pt, processus pterygoideus; sol-n, solum nasi; t-m, taenia marginalis; tr-cr, trabecula cranii; tt-p, tectum posterius.  
Three-dimensional reconstruction of the chondrocranium of C. aeneus (4.9 mm SL). (a) Dorsal view. (b) Ventral view of the neurocranium. (c) Right lateral view. apal, autopalatinum ; c-ac, cartilago acrochordalis; c-eth, cartilago ethmoideum; ch, ceratohyale; cm-bc-a, commissura basicapsularis anterior; cm-bc-p, commissura basicapsularis posterior; cm-bv, commissura basivestibularis; c-Meck, cartilago Meckeli; cm-lat, commissura lateralis; cm-spheth, commissura sphenoethmoidalis; cmsphsep , commissura sphenoseptalis; c-ot, otic capsule; c-pc, cartilago parachordalis; fn-bc-a, fenestra basicapsularis anterior; fn-hyp; fenestra hypophysea; fr-A, foramen ''A''; fr-IX, foramen nervus glossopharyngeus (fenestra basicapsularis posterior); fr- X, foramen nervus vagus; hh, hypohyale; hs, hyosymplecticum; ih, interhyale; lm-on, lamina orbitonasalis; not, notochord; pnsep , pons epiphysialis; pr-pt, processus pterygoideus; q, quadratum ; sol-n, solum nasi; t-m-a, taenia marginalis anterior; t-m-p, taenia marginalis posterior; tr-cr, trabecula cranii; tt-p, tectum posterius.  
Callichthyids take a basal position in the loricarioid evolutionary lineage leading up to an algae scraping feeding mechanism in the loricariid family. Therefore, the study of the morphology and development of a callichthyid representative would contribute to a better knowledge on the differences in cranial morphology and their impact on feeding ecology within this superfamily. Therefore, development in the chondrocranium of Corydoras aeneus was studied based on 22 cleared and stained specimens and 6 series of serial sections. The latter sections were also digitized and used for 3D reconstructions. Development overall follows the typical siluriform trends in chondrocranial development. Even the low complexity of the chondrocranium at hatching fits the trend observed in other siluriforms, although other studies showed loricarioid hatchlings to generally show more complex chondrocrania. In contrast to other catfish, in C. aeneus, the notochord was never found to protrude into the hypophyseal fenestra. In addition, also differing from other siluriforms, a commissura lateralis is present, a state also reported for Ancistrus cf. triradiatus (Geerinckx et al., [2005] J Morphol 266:331-355). The splanchnocranium again has the typical siluriform shape during its ontogeny, with the presence of a compound hyosymplectic-pterygoquadrate plate, although not fused to the neurocranium or interhyal at any time during ontogeny, a state described earlier for Callichthys callichthys (Hoedeman, [1960a] Bull Aquat Biol 1:73-84; Howes and Teugels, [1989] J Zool Lond 219:441-456). The most striking difference found in comparison to other catfishes, however, involves thebranchial basket, which arises as a single element with a further differentiation from the middle arches on in both a rostral and caudal direction.
Development in the osteocranium of Corydoras aeneus was studied based on 48 cleared and stained specimens and 10 series of serial sections. Development overall follows the general trends observed in siluriform development, with ossifications appearing as a response to functional demands. Early development of the skull occurs in two distinct phases. In a first phase, several new bony elements, all of dermal origin and related to feeding, appear shortly after yolk depletion (4.4 mm SL). Between 5 and 8 mm SL, developmental priorities seem to shift to size increase of the cartilaginous skull and no new bony elements appear. Finally, a second phase of osteogenesis occurs from 8 to 18 mm SL, in which all remaining dermal and perichondral bones appear.
The excretory organs of the freshwater polychaete Hypania invalida have been examined using scanning and transmission electron microscopy. Three pairs of macroscopically and ultrastructurally different nephridia are present in the thorax. Intersegmental septa in the thorax are absent, with the exception of a single diaphragm between second and third chaetiger. The first pair of nephridia is anterior to this septum, the second pair crosses the septum, with the nephrostomes anterior and the ducts and the nephridiopori posterior to it, and the third pair of nephridia is entirely posterior to the diaphragm. The first two pairs of nephridia have ciliated nephrostomes of moderate size and long nephridial ducts that extend the length of the thorax. In contrast, the third pair is characterized by short ducts and very prominent nephrostomes. Macroscopically, seven different sections of nephridial duct cells can be distinguished along the length of the first two pairs of nephridia, whereas, on an ultrastructural basis, only six different regions can be identified. Only two regions of different duct cells can be recognized in the third pair of nephridia. Cells of the two anterior pairs of nephridia show typical characteristics of transport epithelia and most likely function as excretory organs. In contrast, the duct cells of the third pair are not that much differentiated and might primarily be responsible for the release of sexual products, as sperm was observed passing through these ducts. Podocyte-like cells were observed to accompany nephridial ducts.
Female insects generally store sperm received during mating in specific organs of their reproductive tract, i.e., the spermathecae, which keep the sperm alive for a long time until fertilization occurs. We investigated spermatheca morphology and ultrastructure in the psylloidean insect Trioza alacris (Flor,1861) in which spheroidal sperm packets that we refer to as 'spermatodoses' are found after mating. The ectoderm-derived epithelium of the sac-shaped spermatheca that has a proximal neck, consists of large secretory and flat cuticle-forming cells. Secretory cells are characterized by a wide extracellular cavity, bordered by microvilli, in which electron-dense secretion accumulates before discharge into the spermathecal lumen. The cuticle-forming cells produce the cuticular intima of the organ and a peculiar specialized apical structure, through which secretion flows into the lumen. At mating, the male transfers bundles of sperm cells embedded in seminal fluid into the spermathecal neck. Sperm cells proceed towards the spermathecal sac lumen, where they are progressively compacted and surrounded with an envelope that also encloses secretions of both male and female origin. We describe the formation of these sperm containing structures and document the contribution of the female secretion to spermatodose or female-determined spermatophore construction. We also discuss the choice of the term 'spermatodose' for T. alacris and suggest it be used to refer to sperm masses constructed in the female reproductive organs, at least when they involve the contribution of female secretion.
Recent reports of high frequency sound production by cusk-eels cannot be explained adequately by known mechanisms, i.e., a forced response driven by fast sonic muscles on the swimbladder. Time to complete a contraction-relaxation cycle places a ceiling on frequency and is unlikely to explain sounds with dominant frequencies above 1 kHz. We investigated sonic morphology in the fawn cusk-eel Lepophidium profundorum to determine morphology potentially associated with high frequency sound production and quantified development and sexual dimorphism of sonic structures. Unlike other sonic systems in fishes in which muscle relaxation is caused by internal pressure or swimbladder elasticity, this system utilizes antagonistic pairs of muscles: ventral and intermediate muscles pull the winglike process and swimbladder forward and pivot the neural arch (neural rocker) above the first vertebra backward. This action stretches a fenestra in the swimbladder wall and imparts strain energy to epineural ribs, tendons and ligaments connected to the anterior swimbladder. Relatively short antagonistic dorsal and dorsomedial muscles pull on the neural rocker, releasing strain energy, and use a lever advantage to restore the winglike process and swimbladder to their resting position. Sonic components grow isometrically and are typically larger in males although the tiny intermediate muscles are larger in females. Although external morphology is relatively conservative in ophidiids, sonic morphology is extremely variable within the family.
To date only few comparative approaches tried to reconstruct the ontogeny of the musculature in invertebrates. This may be due to the difficulties involved in reconstructing three dimensionally arranged muscle systems by means of classical histological techniques combined with light or transmission electron microscopy. Within the scope of the present study we investigated the myogenesis of premetamorphic, metamorphic, and juvenile developmental stages of the anaspidean opisthobranch Aplysia californica using fluorescence F-actin-labeling in conjunction with modern confocal laser scanning microscopy. We categorized muscles with respect to their differentiation and degeneration and found three true larval muscles that differentiate during the embryonic and veliger phase and degenerate during or slightly after metamorphosis. These are the larval retractor, the accessory larval retractor, and the metapodial retractor muscle. While the pedal retractor muscle, some transversal mantle fibers and major portions of the cephalopedal musculature are continued and elaborated during juvenile and adult life, the buccal musculature and the anterior retractor muscle constitute juvenile/adult muscles which differentiate during or after metamorphosis. The metapodial retractor muscle has never been reported for any other gastropod taxon. Our findings indicate that the late veliger larva of A. californica shares some common traits with veligers of other gastropods, such as a larval retractor muscle. However, the postmetamorphic stages exhibit only few congruencies with other gastropod taxa investigated to date, which is probably due to common larval but different adult life styles within gastropods. Accordingly, this study provides further evidence for morphological plasticity in gastropod myogenesis and stresses the importance of ontogenetic approaches to understand adult conditions and life history patterns.
Mouthpart and alimentary canal development was examined in Lysmata amboinensis larvae using scanning electron microscopy and histology. The gross morphological features of external mouthparts and internal digestive tract structures of larvae at different developmental stages indicate that ingestive and digestive capabilities are well developed from early on. With increasing age of the larvae the mouthpart appendages increased in size, the hepatopancreas in tubular density and the midgut in length. The density of setae and robustness of teeth and spines of individual structures increased. The most pronounced changes from early to late stage larvae involved formation of pores on the paragnaths and labrum, transformation of the mandibular spine-like teeth to molar cusps, development of the filter press in the proventriculus and of infoldings in the previously straight hindgut. The results suggest that early stage L. amboinensis larvae may benefit from soft, perhaps gelatinous prey, whereas later stages are better equipped to handle larger, muscular or more fibrous foods.
The cyprinodontiform family Goodeidae comprises two biogeographically disjunct subfamilies: the viviparous Goodeinae endemic to the Mexican Plateau, and the oviparous Empetrichthyinae, known only from relict taxa in Nevada and California. Ovarian characteristics of two oviparous species of goodeid, Crenichthys baileyi and Empetrichthys latos, studied using museum collections, are compared with those of viviparous species of goodeids. Both subfamilies have a single, cystovarian ovary. The ovary in the viviparous Goodeinae has an internal septum that divides the ovarian lumen into two compartments, and it may possess oogonia. There is no ovarian septum in the oviparous C. baileyi and E. latos. Oogenesis is similar in both subfamilies with regard to the proliferation of oogonia, initiation of meiosis, primary growth and development of an oocyte during secondary growth in which fluid yolk progressively fuses into a single globule. Notably, eggs of C. baileyi and E. latos are approximately double the size of those of the viviparous Goodeinae in which embryos develop inside the ovarian lumen and are nourished, in part, by nutrients transferred from the maternal tissues, a mode of embryo development called matrotrophy. Egg envelopes of the two subfamilies differ in that those of C. baileyi and E. latos have a relatively thick zona pellucida, attachment fibrils or filaments that develop between the follicle cells during oogenesis, and a micropyle observed only in E. latos. In contrast, viviparous goodeid eggs have a relatively thin zona pellucida, but lack adhesive fibrils, and a micropyle was not observed. These reproductive characters are compared with those of species of the eastern North American Fundulus, a representative oviparous cyprinodontiform. One newlyrecognized shared, derived character, a single, median ovoid ovary with no obvious external evidence of fusion, supports monophyly of the Goodeidae. Differences among the goodeid subfamilies and Fundulus are interpreted relative to the oviparous versus viviparous modes of reproduction.
Chick embryo vertebral development has been studied during the period from 3 to 19 days of incubation. Whole mount preparations stained with alcian blue for cartilage and alizarin red for bone show the vertebral bodies as cartilaginous at 5 days, with dorsal spinous processes at 6 1/2 days, the onset of bone formation at the ventral and dorsal surfaces of the bodies at 13 days, ossification extending dorsally within the neural arches at 13 1/2 days, and bone development occurring throughout the vertebrae at 16 days. Descriptions at each time period center on the thoracic vertebrae with occasional inclusion of adjacent lower cervical and upper lumbar vertebrae. Histologic development is correlated with the Hamburger-Hamilton stages, which are based on external characteristics. The notochord and neural tube are well developed by 3 days and surrounded by sclerotome, myotome, and dermatome cells. Cartilage formation in the perinotochordal region of the vertebral body is seen at 5 days and precedes development of the neural arches and spinous processes. Separate centers of chondrocyte hypertrophy occur in the body (9 days), the lateral neural arches and the dorsal spinous process. Bone formation is under way at 13 days, beginning in the vertebral bodies. Intramembranous periosteal bone formation is seen adjacent to internal regions of chondrocyte hypertrophy. Vascular invasion of hypertrophic chondrocyte regions occurs, but the mechanism of endochondral ossification differs from that of mammals. The cartilage is resorbed by multinucleated chondroclasts and marrow round cells. Clumps of growth plate cartilage cells and matrix are surrounded occasionally by newly synthesized bone, but invasion of individual hypertrophic chondrocyte lacunae by vessels with bone deposition by accompanying osteoblasts on single trabeculae of cartilage does not occur. 3H-thymidine autoradiography shows high uptake at 3 and 5 days in the germinal neuroepithelial cells of the neural tube (spinal cord) and notochord. By 7 days, notochordal uptake is markedly diminished, and no uptake of isotope occurs from 8 days onward. Spinal cord uptake is highest in the first 8 days but persists in lessened amounts to 19 days. From 5 days onward, both undifferentiated mesenchymal cells and differentiated chondrocytes show positive 3H-thymidine uptake, but labeling is never seen in hypertrophic chondrocytes.
A century ago, Carl Gegenbaur's program of vertebrate evolutionary morphology faced its greatest challenges. The controversy over the evolutionary origin of the vertebrate paired limbs between 1875 and 1906 illustrates the failure of the traditional methods of comparative anatomy and embryology (supported by Haeckel's biogenetic law) to choose between different phylogenetic hypotheses. The controversy over morphology's status as science intensified at the turn of the twentieth century, when the legitimacy of historical explanation itself as a mode of scientific understanding came under fire. Gegenbaur's intellectual grandson, Hermann Braus, sought to defend the legitimacy of phylogenetic reconstruction while updating it to include experimental and causal-analytical approaches, but was unable to sustain a viable synthetic research program. The article concludes with reflections on approaches to the past used by historians and evolutionary morphologists.
Intraocellar glands in Craterostigmus tasmanianus . A: Semithin section through the ventral half of the left eye (pos- 
The lateral lens eye of adult Craterostigmus tasmanianus Pocock, 1902 (a centipede from Australia and New Zealand) was examined by light and electron microscopy. An elliptical, bipartite eye is located frontolaterally on either side of the head. The nearly circular posterior part of the eye is characterized by a plano-convex cornea, whereas no corneal elevation is visible in the crescentic anterior part. The so-called lateral ocellus appears cup-shaped in longitudinal section and includes a flattened corneal lens comprising a homogeneous and pigmentless epithelium of cornea-secreting cells. The retinula consists of two kinds of photoreceptive cells. The distribution of the distal retinula cells is highly irregular. Variable numbers of cells are grouped together in multilayered, thread-like unions extending from the ventral and dorsal margins into the center of the eye. Around their knob-like or bilobed apices the distal retinula cells give rise to fused polymorphic rhabdomeres. Both everse and inverse cells occur in the distal retinula. Smaller, club-shaped proximal retinula cells are present in the second (limited to the peripheral region) and proximal third of the eye, where they are arranged in dual cell units. In its apical region each unit produces a small, unidirectional rhabdom of interdigitating microvilli. All retinula cells are surrounded by numerous sheath cells. A thin basal lamina covers the whole eye cup, which, together with the distal part of the optic nerve, is wrapped by external pigment cells filled with granules of varying osmiophily. The eye of C. tasmanianus seemingly displays very high complexity compared to many other hitherto studied euarthropod eyes. Besides the complex arrangement of the entire retinula, the presence of a bipartite eye cup, intraocellar exocrine glands, inverse retinula cells, distal retinula cells with bilobed apices, separated pairs of proximal retinula cells, medio-retinal axon bundles, and the formation of a vertically partitioned, antler-like distal rhabdom represent apomorphies of the craterostigmomorph eye. These characters therefore collectively underline the separate position of the Craterostigmomorpha among pleurostigmophoran centipedes. The remaining retinal features of C. tasmanianus agree with those known from other chilopod eyes and, thus, may be considered plesiomorphies. Characters like the unicorneal eye cup, sheath cells, and proximal rhabdomeres with interdigitating microvilli were already present in the ground pattern of the Pleurostigmophora. Other retinal features were developed in the ancestral lineage of the Phylactometria (e.g., large elliptical eyes, external pigment cells, polygonal sculpturations on the corneal surface). The homology of all chilopod eyes (including Notostigmophora) is based principally on the possession of a dual type retinula.
We describe the ultrastructural organization of the anal organs of Craterostigmus tasmanianus, which are located on the ventral side of the bivalvular anal capsule. Each part of the capsule bears four pore fields with several anal pores. The pores lead into a pore canal, which is surrounded by the single-layered epithelium of the anal organs. Each anal organ is composed of four different cell types: transporting cells of the main epithelium, junctional cells, isolated epidermal glands, and the cells forming the pore canal. The transporting cells exhibit infoldings of the outer cell membranes, forming a basal labyrinth and a poorly developed apical complex. The cells are covered by a specialized cuticle with a widened subcuticular layer. Only the cuticle of the main epithelium is covered by a mucous layer, secreted by the epidermal glands. The ultrastructural organization of the anal organ is comparable to the coxal and anal organs of other pleurostigmophoran Chilopoda. It is likely that the coxal and anal organs of the Pleurostigmophora are homologous, due to their identical ultrastructural organization. Differences concerning the location on the trunk of Pleurostigmophora are not sufficient to reject a hypothesis of homology. Anal organs are found not only in Craterostigmomorpha, but also in most adult Geophilomorpha, and in larvae and most adults of Lithobiomorpha. The anal organs of C. tasmanianus are thought to play an important role in the uptake of atmospheric water. J. Morphol.
Top-cited authors
George V. Lauder
  • Harvard University
Robin Adair Wallace
  • University of Florida
Brian K Hall
  • Dalhousie University
Marvalee H Wake
  • University of California, Berkeley
Kelly Selman
  • University of Florida