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New outlook on the system of chitons (Mollusca: Polyplacophora)

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... Adicionalmente se revisaron los registros de especies identificadas en el Museo Nacional de Historia Natural, USNM (http://invertebrates.si.edu/antiz/). Campañas BENTART 2003-2006 El área de estudio fue la zona occidental de la Península Antártica, desde las Islas Shetland del Sur hasta el Mar de Bellingshausen frente a la Isla Thurston (Fig. 1). A bordo del B/O Hespérides fueron obtenidas muestras bentónicas entre 5 y 2044 m de profundidad, utilizando diversos artes de muestreo: rastra Agassiz, rastra de roca, box-corer, trineo suprabentónico y buceo SCUBA (ver Aldea & Troncoso, 2008). ...
... Todos los especímenes recolectados fueron separados, fijados en etanol (70%) identificados a nivel de especie y registrados en la base de datos. Su clasificación taxonómica se realizó en base a Sirenko (2006) y Gofas (2013). Para efectos de consulta se mantienen en la colección del Departamento de Ecología y Biología Animal de la Universidad de Vigo (España). ...
... The remains of the radula and girdle were dried and embedded in Canada balsam for examination under a light microscope. The taxonomic arrangement follows Sirenko (2006). & Hull, 1924 Type species. ...
... Such plasticity of morphological characters has led to the uncritical inclusion of several genera within the family, and it is not surprising that Okusu et al. (2003), in the first phylogenetic study of polyplacophorans, revealed a polyphyly not only for the family but also for Ischnochi ton, its type genus. Later, Sirenko (2006) re-arranged taxa, but the monophyly of Ischnochiton was still not solved (Irisarri et al. 2020). Noteworthy in this context is the lack of any genetic information for Chiton texti lis Gray, 1828, the type species of Ischnochiton, and this makes it almost impossible to understand the true character of this genus and confirm the taxonomic position of species currently placed in Ischnochiton. ...
... It is possible that the depauperate fossil record of chitons in the southeastern Pacific could be related to scarce effort in chiton fossil research in this region. Fossils of Tonicia have been found in the Beagle Channel dating back 7500 years (Holocene; Sirenko, 2006b;Puchalski et al., 2009;Gordillo & Schwabe, 2009), which could be considered a minimal date of origin that, in conjunction with our much older molecular estimation, extends the time interval of origin of the genus Tonicia to the Eocene, in agreement with Sirenko (2006b). In addition, the dated phylogeny generated in the present study shows that T. forbesii from Mexico and the lineage of all SEP Tonicia species share an ancestor that originated ~46 Mya. ...
... It is possible that the depauperate fossil record of chitons in the southeastern Pacific could be related to scarce effort in chiton fossil research in this region. Fossils of Tonicia have been found in the Beagle Channel dating back 7500 years (Holocene; Sirenko, 2006b;Puchalski et al., 2009;Gordillo & Schwabe, 2009), which could be considered a minimal date of origin that, in conjunction with our much older molecular estimation, extends the time interval of origin of the genus Tonicia to the Eocene, in agreement with Sirenko (2006b). In addition, the dated phylogeny generated in the present study shows that T. forbesii from Mexico and the lineage of all SEP Tonicia species share an ancestor that originated ~46 Mya. ...
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The chiton genus Tonicia is composed of 12 species, 11 of which are found in the eastern Pacific, but the taxonomic status and geographical distribution of these species have long been controversial. In this study, we compare eastern Pacific Tonicia species using molecular systematics. The molecular markers cytochrome oxidase c subunit I (COI), 16S and 18S ribosomal RNA were used to estimate the phylogenetic relationships and divergence times among species. Species delimitations were inferred using a Bayesian generalized mixed Yule coalescent (bGMYC) and a Bayesian Poisson tree processes (bPTP) approach. We assigned southeastern Pacific specimens to nine recognized species based on their morphology, but these were resolved into only six species in our molecular phylogeny, suggesting that three of the recognized morpho species need to be synonymized. The bGMYC and bPTP analyses indicate the existence of six total coalescent groups interpreted as seven species in our gene tree results. Likewise, pairwise genetic distances, phylogenetic estimates and coalescent approaches support only seven lineages when considering specimens that match the nine currently recognized southeastern Pacific Tonicia species. We suggest that the colouration and morphological characters used to identify Tonicia species must be re-examined in depth.
... About the reproductive system of Callistochiton righii, we could not detect different sexes in the analyzed specimens, as observed in Barbosa et al. (2009). That author analysed species of Acanthopleura gemmata (Blainville, 1825), which belong to the same suborder (Sirenko, 2006), and indicated gonads of different colours for males and females. ...
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Callistochiton righii is reviewed based on preserved specimens collected in northeastern Brazil. A complement ary description based on detailed anatomical data is presented and comparisons with other local species are provided. Its distribution is extended about 2,200km northward and about 1,000km southward compared to the previously known range.
... At the same time, it should be recalled that Sirenko (2006) transferred the genus Ceratozona Dall, 1882 from the suborder Chitonina to the suborder Acanthochitonina Bergenhayn, 1930 because both species of the genus have abanal gills and pointed ventral spicules. Arrangement of pores between gills counted from the last one in both species of the genus [Ceratozona squalida (C.B. ...
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A new genus and new species of the family Callistoplacidae from the bathyal zone near Guadeloupe Island in the Caribbean Sea are described. Caribbochiton guadeloupensis n. gen. et n. sp. is unlike other genera in the family Callistoplacidae: it has no ribs on end valves or on lateral areas of intermediate valves. According to other morphological features (thick shell, relatively narrow valves, noticeably raised lateral areas, similar slit formula, insertion plate teeth thickened at edges of slits, dorsal scales), this genus is closest to the family Callistoplacidae. Given that a number of species of the family do not have at a young age the ribs which appear later, we hypothesise that the new genus could have evolved as a result of paedomorphosis. An emended diagnosis of the family Callistoplacidae is hereby proposed. ZooBank registration: LSIDurn:lsid:zoobank.org:pub:BB94DD8F-C466-4B1B-8868-EEAB75E6930B Carribochiton LSIDurn:lsid:zoobank.org:act:EBD4411B-C39D-446C-AD24-EB5F3A27AB32 Carribochiton guadeloupensis LSIDurn:lsid:zoobank.org:act:19B8AF77-2AB8-4BD1-940A-CA4EAFFCF215
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An assemblage of 34 chiton valves collected from rocks of the “Imperial” Formation sensu lato at Super Creek near Palm Springs, California, is described here. The sedimentary rocks exposed at Super Creek were deposited in the proto-Gulf of California during the Late Miocene. This chiton assemblage represents the first reported Miocene chitons from western North America. The chiton valves are classified as Callistochiton cf. C . elenensis , Chaetopleura cf. C . lanuginosa mixta , Calloplax roederi n. sp., Chiton solaris n. sp., Callistoplacidae sp. indet., and Chaetopleuridae sp. indet. Thick valves dominate the assemblage. The chiton fossils reflect the overall faunal pattern from the “Imperial” Formation s.l. of a strong similarity to taxa in the modern Gulf of California, with a Caribbean component as well. This assemblage fills a gap in the chiton fossil record and preserves details of the adaptive radiation of the Polyplacophora that occurred at the time in concert with the onset of an upwelling regime. UUID: http://zoobank.org/9947bfc9-84a3-4358-bac7-e660b936b067
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Based on extensive new material, 2088 valves resulting from search sampling of ~500 kg of sediment, the Pliocene chiton biodiversity of the Mondego Basin (Portugal) is reassessed. Twelve species were identified, assigned to seven genera. Eight species are new for the Pliocene of Portugal, as well as two of the genera: Hanleya, Acanthochitona . Two taxa are described as new: Ischnochiton loureiroi n. sp. and Lepidochitona rochae n. sp. Until now, the polyplacophoran European Neogene record was too poorly known to be of help in generating a clear picture of the Miocene to present-day biogeography of the group. This new wealth of data from western Iberia, in conjunction with recent data from the Loire Basin Upper Miocene assemblages (France), allows clarification the Late Miocene to Recent eastern Atlantic and Mediterranean biogeography of the Polyplacophora. The northern range of warm-water northeast Atlantic and Mediterranean Polyplacophora experienced a sharp contraction since, at least, Late Miocene to Early Pliocene times. Warm-water chiton species represented in the Upper Miocene of the Loire Basin of NE France (European-West African Province) and the Pliocene of the Mondego Basin of central-west Portugal (Pliocene French-Iberian Province) are today confined to the southern Mediterranean-Moroccan Molluscan Province. UUID: http://zoobank.org/a2a550c0-caed-449a-aa45-9492c45f882e
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The chiton Liolophura japonica (Lischke 1873) is distributed in intertidal areas of the northwestern Pacific. Using COI and 16S rRNA, we found three genetic lineages, suggesting separation into three different species. Population genetic analyses, the two distinct COI barcoding gaps albeit one barcoding gap in the 16S rRNA, and phylogenetic relationships with a congeneric species supported this finding. We described L. koreana, sp. nov. over ca. 33°24′ N (JJ), and L. sinensis, sp. nov. around ca. 27°02′–28°00′ N (ZJ). We confirmed that these can be morphologically distinguished by lateral and dorsal black spots on the tegmentum and the shape of spicules on the perinotum. We also discuss species divergence during the Plio-Pleistocene, demographic expansions following the last interglacial age in the Pleistocene, and augmentation of COI haplotype diversity during the Pleistocene. Our study sheds light on the potential for COI in examining marine invertebrate species discrimination and distribution in the northwestern Pacific.
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The phylogenetic relationships within the molluscan class Polyplacophora (chitons) have been studied using morphology, traditional Sanger markers and mitogenomics, but, to date, no analysis has been carried out using transcriptomic and genome-wide data. Here, we leverage the power of transcriptomes to investigate the chiton phylogeny to test current classification schemes and the position of Callochitonidae, a family whose phylogenetic position and taxonomic assignation are uncertain because of conflicting results from past studies. Using multiple data matrices with different taxon occupancy thresholds and inference methods, including both concatenated and coalescence-based approaches, we find a consistent resolution of the chiton phylogeny. Our results support a system with the orders Lepidopleurida, Chitonida and Callochitonida, with the latter two as sister groups. This resolution is compatible with recent mitogenomic results and rejects the position of Callochiton as a member of Chitonina.
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Molluscs biomineralize structures that vary in composition, form, and function, prompting questions about the genetic mechanisms responsible for their production and the evolution of these mechanisms. Chitons (Mollusca, Polyplacophora) are a promising system for studies of biomineralization because they build a range of calcified structures including shell plates and spine- or scale-like sclerites. Chitons also harden the calcified teeth of their rasp-like radula with a coat of iron (as magnetite). Here we present the genome of the West Indian fuzzy chiton Acanthopleura granulata, the first from any aculiferan mollusc. The A. granulata genome contains homologs of many genes associated with biomineralization in conchiferan molluscs. We expected chitons to lack genes previously identified from pathways conchiferans use to make biominerals like calcite and nacre because chitons do not use these materials in their shells. Surprisingly, the A. granulata genome has homologs of many of these genes, suggesting that the ancestral mollusc may have had a more diverse biomineralization toolkit than expected. The A. granulata genome has features that may be specialized for iron biomineralization, including a higher proportion of genes regulated directly by iron than other molluscs. A. granulata also produces two isoforms of soma-like ferritin: one is regulated by iron and similar in sequence to the soma-like ferritins of other molluscs, and the other is constitutively translated and is not found in other molluscs. The A. granulata genome is a resource for future studies of molluscan evolution and biomineralization.
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Chitonida (Mollusca: Polyplacophora) на основе корреляции между типом расположения жабр и формой придатков хориона Б.И.СИРЕНКО Зоологический институт РАН, Санкт-Петербург, 199034 Университетская набережная, 1 На богатом оригинальном материале с использованием литературных данных изучено разнообразие форм придатков вторичной яйцевой оболочки, или хориона у 112 видов панцирных моллюсков отряда Chitonida, а также типы расположения жабр у 138 видов. Отмечено большое разнообразие форм придатков хориона. Обнаружена необычная корреляция между формой придатков хориона и типом расположения жабр. Оказалось, .что для хитонов с абанальным типом располо­ жения жабр характерны немногочисленные крупные объемистые придатки хорио­ на, в то время как для видов с аданальными жабрами-многочисленные мелкие тонкие придатки. Вопреки прежним представлениям, предложена новая форму­ лировка аданального типа расположения жабр, характерного лишь для тех видов, у которых назад от нефропора располагается не менее 3 жабр, тогда как при абанальном типе сзади от нефропора имеется лишь одна жабра. На основании упорядочения типов расположения жабр проведена ревизия системы панцирных моллюсков отряда Chitonida, получившая дополнительное подтверждение в строении придатков хориона. Представлена новая система хитонов отряда Chitonida, в которой вместо трех подотрядов оставлено только два: Chitonina и Acanthochitonina. В первый вошли семейства с аданальным типом расположения жабр и мелкими тонкими придатками хориона яйца, а во второй-с абаналь­ ным типом расположения жабр и крупными объемистыми придатками хориона. В подотряд Acanthochitonina отнесены также все семейства прежнего подотряда Tonicellina. Due to the ambiguity of definitions of abanal (= metamacrobranches) and adanal (= mesomacrobranches) types of the gill arrangement given by Plate [1896, 1901 ] and Pelseneer [1898,1899 ], the species of the genera Chaetopleura, Callistochiton, Stenoplax and others are considered to be different in this respect. Accepting the assumption of Pelseneer [1898, 1899 J that the paired gills situated immediately behind the nephropore represented the ancestral state whereas other gills appeared later in the phylogenesis of chitons, as a result of increase in their number only onward (abanal type) or onward and backward (adanal type) from the initial pair of gills, we think that the basic character permitting faultless determination of the gill arrangement is the position of nephropore in relation to the gills. In our opinion only the species having one gill behind the nephropore should be regarded as those with abanal type. All other species having 3 and more gills behind the nephropore are considered as species with adanal type.
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Transmission electron microscopy of the spermatozoa and spermatogenesis of 11 species (in three suborders Chitonina, Acanthochitonina, Lepidopleurina) of chiton has shown that each species has a sperm with a unique morphology indicating that spermatozoa can be used as a taxonomic character. Although structure is species-specific, similarities between species within suborders and subfamilies can be recognized. The spermatozoa of species from the suborders Chitonina and Acanthochitonina have a head comprising nuclear material only, the anterior portion of which is in the form of a long thin (approximately 80 nm diameter) filament. In many species the centrioles and mitochondria of the midpiece are lateral in position, the mitochondria often being sited anteriorly alongside the nucleus. By contrast, Leptochiton asellus, a member of the more ancient suborder Lepidopleurina, has a sperm with a head comprising a nucleus and an acrosome. The mid-piece is also more conventional in structure with a ring of five or six spherical mitochondria (sited behind the nucleus) that surround the centrioles. The presence of the acrosome in L. asellus suggests that in the more recent chitons the acrosome has been secondarily lost. It is proposed that loss of the acrosome is correlated to a modification in egg-coat thickness. A preliminary examination of the structure of the eggs of three species has shown that those of L. asellus are surrounded by a very thick chorion (14-30 mu m) whereas in Acanthochitona crinitus and Dinoplax gigas there are regions of the chorion that are less than 2 mu m thick. The morphological changes that occur during spermatogenesis are very similar in the Chitonina and Acanthochitonina. During spermiogenesis the nucleus elongates to develop a long anterior filament. Chromatin condensation within the nucleus involves the formation of fibrils that become orientated along its long axis. Closely associated with the elongating nucleus is a manchette. In L. asellus a spherical proacrosomal vesicle appears in the spermatocytes. This vesicle becomes compressed as it matures and simultaneously it migrates to the presumptive anterior end of the spermatid where it invaginates and elongates. Although the pattern of chromatin condensation in the nucleus is similar to that described above, a manchette has not been observed.
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Echinochiton dufoei new genus and species is described from the Ordovician age Forreston Member, Grand Detour Formation (Blackriveran) near Beloit, Wisconsin. For a variety of reasons, we regard E. dufoei as a chiton; the species is known from four articulated or partially articulated specimens, one of which has eight plates and two of which have a mucro on the tail plate. Echinochiton dufoei differs from other chitons in having large hollow spines that project from each of the known plates. In plate shape and position, E. dufoei is much like the Upper Cambrian species Matthevia variabilis Walcott, 1885, and the Lower Ordovician species Chelodes whitehousei Runnegar, Pojeta, Taylor, and Collins (1979).
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A fine-structural study of fertilization in Callochiton castaneus has revealed that the mechanism of sperm penetration into the egg is intermediate between the primitive condition found in members of the order Lepidopleurida and the more derived condition found in the Chitonida. C. castaneus sperm have the long needlelike nuclear filament and reduced acrosome that characterizes all Chitonida, but they have retained several plesiomorphic features such as an unspecialized mid-piece and a lack of flagellar reinforcement. As in some Lepidopleurida but unlike any Chitonida, the egg hull in this species comprises a thick, smooth jelly coat permeated by pores that permit sperm rapid access to the vitelline layer. The jelly coat is delicate and quickly dissolves when a sperm concentrate is used, suggesting that excess acrosomal enzymes may be responsible. Once the sperm have penetrated the vitelline layer, the long nuclear filament bridges the gap to cups in the egg membrane. However, once the fertilization membrane is raised, the perivitelline space exceeds the length of the nuclear filament, preventing other sperm from penetrating the egg. A fertilization cone forms around the nuclear filament of the penetrating sperm, but it does not appear to engulf the body of the sperm. Rather, the nuclear chromatin is injected into the egg as a long thread. The remaining sperm organelles are apparently abandoned on the egg surface. If this is the case, it would be a significant departure from fertilization in other molluscs and many other metazoans, in which sperm organelles, such as centrioles and mitochondria, enter the egg. New sperm and egg characters, as well as significant differences in fertilization, indicate that Callochitonidae are basal to all other members of the order Chitonida and may warrant separation as the sister taxon to the suborders Chitonina and Acanthochitonina.
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Sperm development, structure of the gametes and some aspects of fertilization in the far-eastern chitons Leptochiton assimilis, Deschayesiella curvata (fam. Leptochitonidae), Tonicella undocaerulea (fam. Tonicellidae), Mopalia retifera (fam. Mopaliidae) and Ischnochiton hakodadensis (fam. Ischnochitonidae) are described by transmission electron microscopy. In the testis spermatogenetic cells are closely associated with auxiliary cells, which are structurally identical to those of other mollusks and probably have a nutritive function. Spermatogenesis in all species did not differ from that of chiton species already studied and it was confirmed that an acrosome is formed from the Golgi apparatus during spermiogenesis. The spermatozoa of all studied species have a structure that is typical for chitons. The sperm of Deschayesiella curvata (Order Lepidopleurida) have a head consisting of a large acrosome and nucleus with an (3.5–4.2μm) asymmetrically positioned anterior extension. The centrioles are surrounded by five spherical mitochondria. The spermatozoa in Tonicella undocaerulea, Mopalia retifera and Ischnochiton hakodadensis (Order Chitonida) have a small acrosome and a nucleus with long thin anterior extension; mitochondria are lateral to the nucleus. There are considerable interspecific differences in the structure of egg envelopes. Our results, along with those of other workers, show that gamete structure of chitons is specific to each family. A cortical reaction which results in formation of a fertilization envelope takes place in the egg of chitons after fertilization.
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The present paper dealing with two new species and one new genus of the Polyplacophora, is the first of a series of reports of systematic study on the deep sea mollusca collected by the research vesselsJINXING andKEXUE I of the Academia Sinica, Institute of Oceanology, during 1978 and 1981 from the continental margin to the bathyal zone of the East China Sea.
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• In considering the Origin of Species, it is quite conceivable that a naturalist, reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts, might come to the conclusion that each species had not been independently created, but had descended, like varieties, from other species. Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified, so as to acquire that perfection of structure and coadaptation which most justly excites our admiration. Naturalists continually refer to external conditions, such as climate, food, &c, as the only possible cause of variation. In one very limited sense, as we shall hereafter see, this may be true; but it is preposterous to attribute to mere external conditions, the structure, for instance, of the woodpecker, with its feet, tail, beak, and tongue, so admirably adapted to catch insects under the bark of trees. In the case of the misseltoe, which draws its nourishment from certain trees, which has seeds that must be transported by certain birds, and which has flowers with separate sexes absolutely requiring the agency of certain insects to bring pollen from one flower to the other, it is equally preposterous to account for the structure of this parasite, with its relations to several distinct organic beings, by the effects of external conditions, or of habit, or of the volition of the plant itself. (PsycINFO Database Record (c) 2012 APA, all rights reserved) • In considering the Origin of Species, it is quite conceivable that a naturalist, reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts, might come to the conclusion that each species had not been independently created, but had descended, like varieties, from other species. Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified, so as to acquire that perfection of structure and coadaptation which most justly excites our admiration. Naturalists continually refer to external conditions, such as climate, food, &c, as the only possible cause of variation. In one very limited sense, as we shall hereafter see, this may be true; but it is preposterous to attribute to mere external conditions, the structure, for instance, of the woodpecker, with its feet, tail, beak, and tongue, so admirably adapted to catch insects under the bark of trees. In the case of the misseltoe, which draws its nourishment from certain trees, which has seeds that must be transported by certain birds, and which has flowers with separate sexes absolutely requiring the agency of certain insects to bring pollen from one flower to the other, it is equally preposterous to account for the structure of this parasite, with its relations to several distinct organic beings, by the effects of external conditions, or of habit, or of the volition of the plant itself. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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Contrary to the widely accepted view that chiton sperm lack acrosomes and that fertilization in this group occurs via a micropyle, we demonstrate here that fertilization in Tonicella lineata occurs by acrosome-mediated sperm-egg fusion. The acrosome is a small vesicle containing two granules located at the tip of the sperm. The eggs have an elaborate hull (= chorion), which is formed into cupules that remain covered by follicle cells until maturity. When dissected ripe eggs were exposed to sperm in vitro, the sperm were attracted only to open cupules, inside which they swam through one of seven channels to the base where they penetrated the hull. The acrosome fired on contact with, or in, the hull, and during passage through it the apical granule was exhausted while the basal granule was exposed. If sperm contacted follicle cells between the cupules the acrosome did not react. The vitelline layer beneath the hull contains pores arranged in a regular pattern. Embedded in the base of each pore is an egg microvillus. Having penetrated the hull the sperm anterior filament located a pore and fused with the tip of the egg microvillus projecting into it. This created a membranous tube, through which the sperm nucleus was injected into the egg. The egg membrane appeared to be raised up into a small fertilization cone around the penetrating sperm, the vitelline layer became slightly elevated, and some cortical granules were released by exocytosis.