A study of the sharks of the suborder Squaloidea

The Denticle Multiverse: Morphological Diversity of Placoid Scales across Ontogeny in the Portuguese Dogfish, Centroscymnus coelolepis, and Its Systematic Implications

Article

Full-text available

Oct 2023
Diversity

Centroscymnus coelolepis is a deep-water sleeper shark and, like most sharks, it is covered in placoid scales, or dermal denticles. The morphological diversity of the dermal denticles in this species, however, has not been described in detail, and ontogenetic changes in denticle morphology are poorly understood in sharks. Combining scanning-electron microscopy and micro-CT imaging, we demonstrate the presence of eleven dermal-denticle morphotypes across the ontogeny and different regions of the body of Centroscymnus coelolepis. The snout, interspiracular, and trunk/tail regions have similar changes in denticle morphotype during development. For example, on the trunks and tails of juveniles (~350 mm TL), denticle crowns have two to three longitudinal ridges and three posterior cusps that are gradually replaced by ridgeless and cuspless crowns in adults (>800 mm TL). Sixteen measurements were obtained from the 3D models generated. A principal component analysis demonstrated that the eleven distinct dermal-denticle morphotypes observed were located in different regions of the morphospace. The denticle volume and surface area showed negative allometry with respect to body length throughout the ontogeny. The results reflect the considerable diversity within the denticle multiverse (ontogenetic and intraspecific variations), and much of this diversity remains to be explored to fully understand the role of dermal denticles in shark taxonomy, ecology, and biomechanics.

Untangling the systematic dilemma behind the roughskin spurdog Cirrhigaleus asper (Merrett, 1973) (Chondrichthyes: Squaliformes), with phylogeny of Squalidae and a key to Cirrhigaleus species

Article

Full-text available

Mar 2023
PLOS ONE

Cirrhigaleus comprises a small genus of rare barbel-bearing dogfish sharks with distributions in limited regions of all oceans. Generic validity and taxonomic status of some species are upon controversies by morphological and molecular evidence that often suggest reallocation of Cirrhigaleus species into the genus Squalus. Particularly, the roughskin spurdog C. asper exhibits intermediary morphological characteristics within Squalidae that requires clarification. In the present study, a phylogenetic approach was undertaken to test the correct generic placement of C. asper using novel and revised morphological characters. We performed maximum parsimony analysis of 51 morphological characters of the internal (e.g., neurocranium, clasper cartilages, pectoral and pelvic girdles) and external anatomy applied to 13 terminal taxa. Cirrhigaleus represents a valid genus and it is supported by eight synapomorphies: high number of monospondylous vertebrae; medial nasal lobe supported by fleshy core and innervated by the buccopharyngeal branch of the facial nerve; neurocranium with greatest width across nasal capsules; one facet and one condyle in the puboischiadic bar for articulating with the basipterygium; two intermediate segments between the basipterygium of the pelvic fin and the axial cartilage of the claspers; five terminal clasper cartilages; and posterior medial process of the puboischiadic bar absent. Cirrhigaleus asper is sister-species to a small clade comprising C. barbifer and C. australis which is supported by one synapomorphy, presence of conspicuous cusplets in the dermal denticles. Cirrhigaleus barbifer, C. asper and C. australis are redescribed herein and the neotype of C. barbifer is designated. A key to Cirrhigaleus species is also given and the inner relationships within Squalus is tentatively discussed.

Revision of the genus Centrophorus (Squaliformes: Centrophoridae): Part 3-Redescription of Centrophorus uyato (Rafinesque) with a discussion of its complicated nomenclatural history

Article

Jun 2022
ZOOTAXA

Centrophorus uyato (Rafinesque, 1810) has a complicated nomenclatural history which has led to multiple scientific names being ascribed to this species. In the Mediterranean Sea, and elsewhere in its range, this species was previously referred to as C. granulosus (Bloch & Schneider, 1801). The first paper in this revision series clarified that C. granulosus refers to a much larger species of gulper shark which attains at least 1.7 m length and is absent from the Mediterranean Sea. Further complicating the nomenclature of this species is the fact that the original description clearly refers to a Squalus species, and not a Centrophorus species. In this third part of the revision of the genus Centrophorus, this problematic species is redescribed. A detailed synonymy is provided and it is confirmed that C. machiquensis, C. bragancae and C. zeehaani are junior synonyms of this species. To preserve nomenclatural stability within the genus, the name Centrophorus uyato is retained for this species with a neotype from close to the original type locality off Italy being designated. Intraspecific variation within Centrophorus uyato is also discussed, particularly relating to denticle morphology and body morphology.

Dental morphology and microstructure of the Prickly Dogfish Oxynotus bruniensis (Squaliformes: Oxynotidae)

Article

Jun 2020

This study describes and illustrates the jaws, teeth, and tooth microstructure of the Prickly Dogfish Oxynotus bruniensis. Detailed accounts of the dental morphology of O. bruniensis are rare and have not addressed the tissue arrangement or microstructure of the teeth. These features are documented and discussed in the contexts of interspecific comparisons with other elasmobranchs and the dietary specialization of O. bruniensis. The overall tooth morphology of O. bruniensis is similar to those of other closely related members in the order Squaliformes, as is the tissue arrangement, or histotype. Oxynotus bruniensis exhibits a simplified enameloid microstructure, which we compare with previously documented enameloid microstructures of other elasmobranchs. Though subtle interspecific differences in dental characters are documented, neither overall tooth morphology nor histotype and microstructure are unique to O. bruniensis. We conclude that in the case of O. bruniensis, dietary specialization is facilitated by behavioral rather than morphological specialization. The Prickly Dogfish is an understudied species of shark. We provide an illustrated account the tooth morphology and microstructure of this species and discuss them in the context of the Prickly Dogfish’s dietary specialization

Cartilaginous fishes offer unique insights into the evolution of the nuclear receptor gene repertoire in gnathostomes

Article

Jun 2020

Nuclear receptors (NRs) are key transcription factors that originated in the common ancestor of metazoans. The vast majority of NRs are triggered by binding to either endogenous (e.g. retinoic acid) or exogenous (e.g. xenobiotics) ligands, and their evolution and expansion is tightly linked to the function of endocrine systems. Importantly, they represent classic targets of physiological exploitation by endocrine disrupting chemicals. The NR gene repertoire in different lineages has been shaped by gene loss, duplication and mutation, denoting a dynamic evolutionary route. As the earliest diverging class of gnathostomes (jawed vertebrates), cartilaginous fishes offer an exceptional opportunity to address the early diversification of NR gene families and the evolution of the endocrine system in jawed vertebrates. Here we provide an exhaustive analysis into the NR gene composition in five elasmobranch (sharks and rays) and two holocephalan (chimaeras) species. For this purpose, we generated also a low coverage draft genome assembly of the chimaera small-eyed rabbitfish, Hydrolagus affinis. We show that cartilaginous fish retain an archetypal NR gene repertoire, similar to that of mammals and coincident with the two rounds of whole genome duplication that occurred in the gnathostome ancestor. Furthermore, novel gene members of the non-canonical NR0B receptors were found in the genomes of this lineage. Our findings provide an essential view into the early diversification of NRs in gnathostomes, paving the way for functional studies.

Taxonomic research on Deania calcea and Deania profundorum (Family: Centrophoridae) in the Cantabrian Sea (Northeast Atlantic) with comments on D. hystricosa

Article

May 2020

Three elasmobranch species of the genus Deania are currently reported in NE Atlantic waters: D. calcea, D. hystricosa and D. profundorum; however, in north Spanish waters (NE Atlantic), only D. calcea and D. profundorum have been caught. Among the criteria used to discriminate Deania species one is dermal denticle length and body colour. In this study the authors explore the feasibility of these criteria and examine other morphological characters to investigate if sexual or ontogenic features had relevance for the distinction of the species particularly those sampled in this study, D. calcea and D. profundorum. Molecular analyses were conducted to validate these results. In D. calcea, dermal denticle length ranged from 340μm to 1400μm (763.2μm ± 180.4 s.d.); in D. profundorum, dermal denticle length ranged from 195μm to 650μm (372.3μm ± 111.7 s.d.). In both Deania species, a significant positive correlation was found between shark total length and dermal denticle length. Dermal denticles varied in size and shape along the shark body. These differences were significant both intra- and inter-specifically. A multivariate analysis based on morphological characters was used to test differences between D. calcea and D. profundorum. The hierarchical analysis clearly identified three groups; two groups corresponded to each species, and a third group discriminated between small and large individuals of D. profundorum. The morphometric characters that contributed most to the divergence between both species were mainly related to the size of the dorsal fins, the inter-dorsal distance and the distances from the snout to the origin of each dorsal fin. Based on morphological characters, no sexual dimorphism was observed. The phylogenetic tree was reconstructed with molecular COI sequences available on BOLD and those obtained in this study. The output tree discriminate D. calcea from D. profundorum, however could not separate molecularly D. calcea and D. hystricosa.

New records and range extension of the Portuguese dogfish Centroscymnus coelolepis in the south‐western Atlantic Ocean, with comments on its morphology

Article

Full-text available

Jan 2020
J FISH BIOL

The Portuguese dogfish Centroscymnus coelolepis is a wide‐ranging deep‐water shark and a common by‐catch component of the catches of several mid‐ to deep‐water fisheries. In the present study, two new records from the south‐western Atlantic Ocean are reported based on specimens caught by bottom‐longline fishing vessels operating in the Argentinean–Uruguayan Common Fishing Zone. Species identification based on morphology and detailed morphometrics, as well as molecular data are presented for one of the specimens. The distribution of the species over the south‐western Atlantic is discussed on the basis of the available bibliography and a thorough revision of museum collections. The records presented here expand the species' previously acknowledged distribution southwards, from around 21° S to at least 38° S, suggesting it occurs continuously along the shelf break of eastern South America. However, given the limited access to specimens of deep‐water sharks in the region, the abundance and real extent of C. coelolepis distribution in the south‐western Atlantic as well as its interaction with deep‐water fisheries remain to be fully assessed.

Molecular diversity and distribution of eastern Atlantic and Mediterranean dogfishes Squalus highlight taxonomic issues in the genus

Article

Dec 2016

The alpha taxonomy of the globally distributed shark genus Squalus has been under intense investigation recently, and many new species have been described over the last decade. However, taxonomic uncertainty remains about several taxa. Without consistent nomenclature and the ability to reliably distinguish between the different Squalus species, basic data collection, downstream conservation and management efforts are seriously compromised. To aid in clarifying the taxonomic status of Squalus species in the eastern Atlantic and Mediterranean, we assessed species diversity at the molecular level and evaluated the consistency in species identification in the region. Samples from all nominal Squalus species recognized in the above regions were collected in an international effort and sequenced for regions of the mitochondrial COI and ND2 genes. These data were further analysed alongside publicly available sequences, including 19 of the 26 Squalus species globally recognized, to compare the regional genus-level diversity with that found elsewhere. Our results confirm inconsistent species identification in the eastern Atlantic and Mediterranean Squalus, particularly concerning S. blainville and S. megalops, and reinforce the need to revise the status of S. megalops and S. mitsukurii as they may include several distinct species distributed around the world. The status of S. blainville is also discussed in the light of the current findings and its problematic taxonomic history.

Molecular diversity and distribution of eastern Atlantic and Mediterranean dogfishes Squalus highlight taxonomic issues in the genus

Article

Dec 2016

The alpha taxonomy of the globally distributed shark genus Squalus has been under intense investigation recently, and many new species have been described over the last decade. However, taxonomic uncertainty remains about several taxa. Without consistent nomenclature and the ability to reliably distinguish between the different Squalus species, basic data collection, downstream conservation and management efforts are seriously compromised. To aid in clarifying the taxonomic status of Squalus species in the eastern Atlantic and Mediterranean, we assessed species diversity at the molecular level and evaluated the consistency in species identification in the region. Samples from all nominal Squalus species recognized in the above regions were collected in an international effort and sequenced for regions of the mitochondrial COI and ND2 genes. These data were further analysed alongside publicly available sequences, including 19 of the 26 Squalus species globally recognized, to compare the regional genus-level diversity with that found elsewhere. Our results confirm inconsistent species identification in the eastern Atlantic and Mediterranean Squalus, particularly concerning S. blainville and S. megalops, and reinforce the need to revise the status of S. megalops and S. mitsukurii as they may include several distinct species distributed around the world. The status of S. blainville is also discussed in the light of the current findings and its problematic taxonomic history.

Not all that clear cut: intraspecific morphological variability in Squalus blainville (Risso, 1827) and implications for identification of the species

Article

Full-text available

Dec 2015

Of the three species of the genus Squalus that occur in the Mediterranean Sea, S. blainville and S. megalops are very difficult to distinguish. This study assesses the variability in morphological features that have been used to differentiate between these species. Squalus were collected from stations within the 25-nautical mile Fisheries Management Zone around the Maltese Islands; 349 specimens were dissected and categorized into male and female, mature and immature, and individuals were randomly selected from each category to make up a sample of 169 specimens. For each individual, total length and first dorsal fin parameters were measured, and morphology of denticles isolated from the laterodorsal area, of the upper and lower teeth and of the chondrocranium was analysed. The first dorsal spine was shorter that the fin base in 93% of the specimens, which is typical of S. megalops ; this character was not related to either gender or maturity. Chondrocrania with one lateral process (typical of S. blainville ) and two lateral processes (typical of S. megalops ) were present. Teeth from the same individuals showed morphological features that overlap between S. blainville and S. megalops . Both unicuspid (typical of S. megalops ) and tricuspid denticles (typical of S. blainville ) were observed on the same individuals. Twelve specimens (six having one and six having two lateral chondrocranial processes) were analysed genetically by sequencing of the mtDNA marker Cytochrome Oxidase Subunit I (COI). All resulted to be S. blainville showing that intraspecific variability in supposedly diagnostic morphological features is large enough to render these unreliable to tell apart these two species, especially in the field.

Distribution and comments on the morphology of Centroscymnus owstonii Garman, 1906 (Squaliformes: Somniosidae), with focus on its occurrence in the Indian Ocean

Article

Sep 2016

The Roughskin Dogfish Centroscymnus owstonii is one of the most widespread deepwater shark species, but its global distribution is mostly based on patchy records. In this study, C. owstonii was reinvestigated with focus on its poorly known distribution in the western and eastern Indian Ocean. Previous records of the species from the Seychelles, which, for decades, were considered to be of a different species, were verified in this study. Furthermore, the first records from off Reunion Island, Madagascar, and Indonesia are provided, including the smallest free-swimming specimen of the species described in detail to date. Based on these specimens, a description of C. owstonii is given with updated and extended morphometric data, photographic documentation and scanning electron microscopy (SEM) images of dermal denticles. Additionally, specimens from the Indian Ocean are compared with specimens from the Pacific and Atlantic Oceans. For the Pacific Ocean, the first record from the central western North Pacific is provided from the Hawaiian-Emperor seamount chain. This record also represents the most open ocean known occurrence of C. owstonii. © 2015 Senckenberg Gesellschaft für Naturforschung and Springer-Verlag Berlin Heidelberg

Taxonomic status of deep-sea sharks Deania calceus and D. hystricosa (Centrophoridae)

Article

Sep 2023

Scymnodon plunketi (Waite, 1910): a junior synonym of Scymnodon macracanthus (Regan, 1906) (Somniosidae: Elasmobranchii)

Article

Full-text available

Apr 2021
J FISH BIOL

Diego F B Vaz

The taxonomic status and validity of Scymnodon macracanthus (Regan, 1906) and Scymnodon plunketi (Waite, 1910) are revised in light of new material from the Southern Pacific and Indian Oceans. Despite being historically accepted as distinct taxa, recent studies suggested the possibility that these species could represent a single taxon. Morphometrics, meristics and morphology of dermal denticles show that S. plunketi is indeed a junior synonym of S. macracanthus. Previous distinctive characters proved to be the result of intraspecific variation. S. macracanthus is therefore redescribed including an updated comparative diagnosis for the genus Scymnodon in the family Somniosidae.

Guia para identificação dos Tubarões, Raias e Quimeras do Rio de Janeiro

Article

Full-text available

Feb 2020

Este trabalho apresenta um guia de identificação simplificado das espécies de tubarões, raias e quimeras (conjuntamente chamados de peixes cartilaginosos) que ocorrem na costa do Estado do Rio de Janeiro, Brasil. Esse trabalho é direcionado a pesquisadores, professores universitários, estudantes de biologia, oceanografia, veterinária, mergulhadores, pescadores, outros profissionais ligados ao mar, e mesmo o público em geral que se interesse pela vida marinha e pelos Chondrichthyes. As chaves de identificação são baseadas em caracteres morfológicos e morfométricos externos, de fácil conferência mesmo por leigos. Para cada ordem, família, gênero e espécie, são apresentados nomes populares, caracteres morfológicos distintivos, faixas de tamanho, distribuição espacial, hábitos e biologia, e outras observações quando pertinentes. Para a área estudada, são reconhecidas neste guia, tubarões: seis ordens, dezenove famílias, trinta e dois gêneros e sessenta e uma espécies; raias: quatro ordens, catorze famílias, vinte e quatro gêneros e trinta e oito espécies; quimeras: uma ordem, três famílias, três gêneros, quatro espécies e, finalmente, quimeras: uma ordem, três famílias, três gêneros e quatro espécies

Identification of Squalus spp. in the Argentine-Uruguayan common fishing zone (ZCPAU) using genetic DNA barcoding

Article

Full-text available

Apr 2025

The Squalus genus is divided into three taxonomic categories that comprise various species, although their nomenclature is frequently inconsistent across different ichthyologists and taxonomies. In the South western Atlantic Ocean, there are three known species of spiny sharks, S. acanthias, S. cubensis, and S. mitsukurii, with discrepant classifications. During campaigns conducted by the INIDEP Chondrichthyan Fisheries Program, 27 Squalus specimens from the Argentine-Uruguayan Common Fishing Zone (ZCPAU) and Argentine coast were collected and morphologically identified onboard. We then coupled DNA COI Barcode technology with BLASTn and BOLD IDS tools to molecularly validate those taxonomic classifications. COI gene sequences were generated for those 27 specimens and compared to available reference sequences (FISHBOL database) from S. acanthias, S. cubensis, S. mitsukurii, S. suckleyi, S. blainville, and S. megalops from different oceanic regions. Genetic distances (K2P) and phylogenetic relationships (via neighbor-joining phylogenetic tree and Median-joining haplotype network) were also estimated for the COI data. A total of thirteen samples identified by the BOLD Identification System did not match the Squalus species identified using morphological evidence. Our analyses also indicated that S. mitsukurii, S. acanthias, and S. cubensis are three clearly distinct species, while S. lobularis is deemed equivalent to S. mitsukurii (K2P=0.35%). Our haplotype network also confirmed the existence of S. acanthias, S. cubensis, and S. mitsukurii in the studied area. The application of these molecular techniques and analyses have proved effective at accurately identifying Squalus species; hence we recommend their use to validate former morphology-based taxonomic identifications.

Confusions across the hemispheres: Taxonomic re-evaluation of two lanternshark species, Etmopterus lucifer and E. molleri (Squaliformes: Etmopteridae)

Article

Full-text available

Mar 2025

The shark genus Etmopterus is the most species-rich shark genus, however, several of its species level taxa pose taxonomic challenges. Especially the Etmopterus lucifer species group is in need of a taxonomic re-evaluation. In the present study, we review the status of E. lucifer and E. molleri from the north- and southwestern Pacific applying an integrative taxonomic approach. Our dataset comprises 100 morphological characters and the mitochondrial NADH2 marker (1,010 bp) for 178 and 83 specimens, respectively. Our results show that E. lucifer and E. molleri from the Northwestern Pacific are distinct from specimens sampled in the Southwestern Pacific. We therefore (1) resurrect E. abernethyi for specimens in the southwestern Pacific hitherto assigned to E. lucifer, (2) synonymize the Northwestern Pacific E. burgessi with E. lucifer and (3) resurrect E. schmidti for specimens in the Northwestern Pacific hitherto assigned to E. molleri. A lectotype is designated herein for E. lucifer. Redescriptions of the four valid species, E. abernethyi, E. lucifer, E. molleri, and E. schmidti, are given and an updated key to all members of the E. lucifer group from the central Indo-Pacific is provided. The current division of the E. lucifer subgroups is challenged, as the key character, the relative length of flank-marking branches, shows great intraspecific variation.

Molecular ecology of the sleeper shark subgenus Somniosus (Somniosus) reveals genetic homogeneity within species and lack of support for S. antarcticus

Article

Dec 2022
J HERED

Inferences made from molecular data support regional stock assessment goals by providing insights into the genetic population dynamics of enigmatic species. Population genomics metrics, such as genetic diversity and population connectivity, serve as useful proxies for species health and stability. Sleeper sharks (genus Somniosus) are ecologically important deep-sea predators, estimated to reach ages of 250-300 years and taking decades to reach sexual maturity. The subgenus Somniosus (Somniosus) is comprised of three species: S. pacificus, S. microcephalus, and S. antarcticus. Given the life history strategy of somniosids, they are vulnerable to overfishing and population declines. Further, data to assess the stocks of these species are limited. To address this deficiency, we used the reduced representation library method Restriction-site Associated DNA sequencing (RADseq) to conduct phylogenomic and population genomics analyses, providing novel information for use in stock assessments. Our results strongly support the species status of S. microcephalus (N = 79), but recover S. antarcticus (N = 2) intermixed within the S. pacificus (N = 170) clade. Population genomics analyses reveal genetic homogeneity within S. pacificus and S. microcephalus, and estimates of effective population size were in the hundreds for both species. Kinship analysis identified two first-degree relative pairs within our dataset (one within each species). Our results contribute new information for stock assessments of these uniquely long-lived species by providing the strongest molecular evidence to date for the synonymization of S. antarcticus and S. pacificus, as well as estimating population genomic metrics for each supported species within the Somniosus (Somniosus) subgenus.

Dermal denticle variations on a newborn Roughskin Dogfish Centroscymnus owstonii (Chondrichthyes: Somniosidae) captured off northeastern Brazil with notes on ontogenetic differentiation

Article

Apr 2021

The Roughskin Dogfish Centroscymnus owstonii is a poorly known species with eventual records along the Western South Atlantic. Different dermal denticles have been historically reported for juveniles and adults, which presupposes changes from a juvenile denticle type to an adult denticle type during growth. The present study was based on a male neonate 324 mm in total length (TL) captured with crab pots on the northeastern continental slope of Brazil, between 400-450 meters. This was considered a newborn based on its small size, very similar to previously reported large embryo dimensions and close to the expected birth size in literature. Three different dermal denticles were observed, alternating from the rostrum to the branchial slits, where a tricuspidated denticle type extended covering the rest of the posterior portion of the body. Dermal denticle types and distribution suggest that the replacement process of dermal denticles begins before birth or early after birth, undergoing at least three changes until reaching the adult dermal denticle type. These different types may be related to uterine epithelial histotroph absorption or embryo movement within the mucous environment, which would be enhanced by largely spaced denticles. The reported fragmented distribution of this species along the Brazilian coast is probably related to insufficient sampling coverage.

Molecular Systematics of the Long-Snouted Deep Water Dogfish (Centrophoridae, Deania) With Implications for Identification, Taxonomy, and Conservation

Article

Full-text available

Jan 2021

According to the most recent taxonomical revision, the deep-sea dogfish genus Deania encompasses four species. Three of them, D. calcea, D. profundorum, and D. hystricosa, occur in the North Atlantic. Whilst D. profundorum can be identified by the presence of a subcaudal keel, the other two species are not easily visually distinguished. Uncertainties over identification raises concerns over stock units and whether management plans are adequate. In this study we compared onboard visual identification of Deania specimens, with morphological inspection of skin denticles under stereo microscope and with independent molecular taxonomical assignment using two molecular markers. Particular emphasis was paid to specimens identified as D. calcea and D. hystricosa in the NE Atlantic where these species potentially occur sympatrically and may be easily confused. In the past the species have been discriminated on the basis of the size of skin denticles (skin roughness), but our study showed that the crown length of skin denticles covaries with size (and sex), irrespective of species, and therefore this is not a reliable morphological character and should not be used to discriminate between the two species. Phylogenetic analyses did not indicate that D. hystricosa to be a distinct lineage from D. calcea. Interestingly, however four individuals (specimens from: UK, Azores Is., Madeira Is. and Seine seamount) formed a well-defined sub-clade nested within the D. calcea clade, possibly a signature of a past vicariance event or a result of coalescent stochasticity.

thesis-volume1: TEXT (in french) "Les Elasmobranches fossiles du Paléogène des Landes (Sud-Ouest, France) Implications dans la connaissance des communautés d’élasmobranches d’eaux profondes. Evolution des Squaliformes et paléoécologie" Fossil selachian teeth from Paleogene of Landes (South-western of France). Implications for the knowledge of deepwater selachian communities. Squaloid evolution and paleoecology.

Thesis

Dec 2000

Sylvain Adnet

Since two centuries, the fossil record of selachians (Sharks, Skates and Rays) is mainly constituted by fossil shallower fishes of epi-continental seas. The discovery of new selachian faunas from the bathyal marls of the Paleogene of Landes (South-western of France) allows to take into account the real diversity of fossil deepwater communities in comparison with the Recent ones. The systematic study of that inedit material fills the considerable gap in our nowledge of the diversity of fossil deepwater selachians. In addition to numerous unnamed taxa, 31 species and 9 genera have been described for the first time, thus testifying to the great diversity of the order Squaliformes (17 species). A cladistic analysis on dental characters of most squaloid genera has been performed, and has led to propose an evolutionary history of Squaliformes. The latter seems to have been strongly related to major events that occurred in cretaceous seas. In a second part, the observation of the global distribution of Recent selachians showed complex but real relationships between the faunal structure and geographic or bathymetric parameters. In this context, several paleoecological approaches have been investigated and tested on selachian faunas, as paleobathymetric and paleogeographic indicators. The interests of such studies are obvious for paleoenvironmental reconstitutions and are discussed. Keywords : Selachians, Paleogene, Landes, Squaloid, cladistic analysis, macroecology, paleoecology

Re-evaluation of deep-sea dogfishes (genus Squalus) in Japan using phylogenetic inference

Article

Mar 2020
DEEP-SEA RES PT I

Japan is known for its marine biodiversity and diverse ecosystem due to its unique geological composition and water currents creating suitable habitats for a wider range of marine species. A rich deep-sea shark community with high endemism occurs on the continental shelf. Yet, the deep-sea shark taxonomy is still under development and poorly documented. Here, a DNA barcoding technique was adopted using the mitochondrial cytochrome oxidase I (COI) and NADH2 genes of samples collected from Japan with additional samples from genetic databases to draft out a phylogenetic tree of the deep-sea shark genus Squalus (dogfishes). The morphological divergence of congeners was further examined. Bayesian and maximum-likelihood-based species-level phylogenetic analyses of mitochondrial COI, ND2 and combined sequences provided strong support for distinct clades corresponding to the parental species with substantial sequence divergence between parental species. The combined dataset of the COI and ND2 gene was most suitable for barcoding of Squalus dogfishes. A multivariate analysis of morphological traits was largely consistent with the genetic data showing small but discrete differences in phenotypic characteristics allowing to separate Squalus species. Genetic samples of the taxonomically problematic Shortspine spurdog ‘Squalus mitsukurii’ from the Atlantic Ocean and Taiwan did not match with the type material of S. mitsukurii Jordan and Snyder, 1903 from mainland Japan. Squalus mitsukurii once considered a globally distributed species is a single, unique spurdog restricted to temperate Japan and Korea and may present an endemic in the Northwestern Pacific. This study further resolved two genetically and phenotypically distinct species of Squalus dogfishes in Japan, one in sympatry with S. mitsukurii in mainland Japan and one in sympatry with subtropical waters associated congeners in the Ryukyu Archipelago. The occurrence of populations of the ‘high-fin’ Taiwan spurdog, Squalus formosus, in subtropical Japan is herein confirmed.

Diet and trophic level of the longnose spurdog, Squalus blainville (Risso, 1826) in the 25-nautical mile Fisheries Management Zone around the Maltese Islands

Article

Mar 2018

The longnose spurdog, Squalus blainville (Risso, 1826), is reported to feed on bony fishes, cephalopods and crustaceans but misidentifications have resulted in ambiguities. This study describes and quantitatively analyses the diet of S. blainville in waters surrounding the Maltese Islands and compares the results with other Mediterranean populations to identify any regional or temporal variation. Additionally, variations in dietary composition with season, maturity, size and sex are investigated for the Maltese population. The diet of 255 individuals, collected from the 25-nautical mile Fisheries Management Zone around the Maltese Islands, was characterised using frequency of occurrence, wet weight and numerical occurrence of food items for sex, maturity, size and seasonal categories. Mediterranean International Trawl Survey (MEDITS) data for the period 2007–2015,which was derived from samples collected within the Food and Agriculture Organisation of the United Nations’s (FAO) General Fisheries Commission for the Mediterranean (GFCM) Geographical Sub-Area 15 (GSA 15), were analysed to identify any relationship between sex, maturity and depth. S. blainville fed on prey items belonging to four main groups: Crustacea, Mollusca, Teleostei and Sipuncula. Mollusca had the highest % IRI (Index of Relative Importance) for the total sample (52.5% of the IRI) and second were teleosts (% IRI=41.4). In terms of habitat, 63.51% of the identified prey categories were demersal, followed by benthic (28.65%) and then pelagic prey categories (7.84%). The highest dietary overlap was observed between seasons, and between immature and mature females; least overlap was between mature and immature males. An increase in size results in more predation especially on cephalopods. Mature and immature individuals were recorded at all depths. Our results indicate that there is some variation in diet between sexes and between maturity stages both in prey items and in the relative contribution of benthic, demersal, and pelagic prey.

Revision of the genus Centrophorus (Squaliformes: Centrophoridae): Part 2--Description of two new species of Centrophorus and clarification of the status of Centrophorus lusitanicus Barbosa du Bocage & de Brito Capello, 1864

Article

Full-text available

Nov 2017

Centrophorus specimens with a distinctive long-based first dorsal fin (long-finned species) have previously been considered to be Centrophorus lusitanicus first described from Portugal. Critical examination of the original description and illustration reveal that C. lusitanicus should be considered a junior synonym of C. granulosus. However, the specimen considered to be the syntype of C. lusitanicus in the Natural History Museum in London is clearly a long-finned species and not conspecific with C. granulosus. A more detailed investigation revealed that this specimen should not be considered a syntype and was likely not originally collected off the coast of Portugal. Investigation of long-finned specimens of Centrophorus from the Indo-West Pacific and Eastern Atlantic revealed that two undescribed species exist and are herein formally described as C. lesliei and C. longipinnis. The two species are similar morphologically and belong to the long- snout Centrophorus group (e.g. C. isodon and C. harrissoni) but are clearly separable based on their very long first dorsal fins. The two species differ in relative length of the first dorsal fin and several other characters. They also differ genetically. Nonmetric multidimensional ordination based on morphometric data reveals both species level and ontogenetic differences. A short erratum is also provided for Part 1 of this revision of the Centrophorus due to two figure related errors which may cause some confusion.

Squalus bassi sp. nov., a new long-snouted spurdog (Chondrichthyes: Squaliformes: Squalidae) from the Agulhas Bank

Article

Sep 2017

Etmopterus samadiae n. sp., a new lanternshark (Squaliformes: Etmopteridae) from Papua New Guinea

Article

Full-text available

Mar 2017

A new species of lanternshark, Etmopterus samadiae (Squaliformes: Etmopteridae), is described from off northern Papua New Guinea, in the western Central Pacific Ocean. The new species resembles other members of the “Etmopterus lucifer” clade in having linear rows of dermal denticles and most closely resembles E. brachyurus from the western North Pacific. The new species occurs along insular slopes between 340 and 785 m depth. The new species can be distinguished from other members of the E. lucifer clade by a combination of characteristics, including length of anterior flank branch mark- ings being slightly shorter than its posterior branch, a longer caudal base marking, and irregular and variable number of black, horizontal, dash-like marks on sides of body. Molecular analysis based on the NADH2 marker further supports the distinction of E. samadiae from other members of the E. lucifer clade.

Chondrichthyes

Chapter

Sep 2016

New record of Zameus squamulosus (Chondrichthyes: Squaliformes: Somniosidae) in the Southern Gulf of Mexico

Article

Full-text available

Dec 2016

Zameus squamulosus is a somniosid shark with a patchy world-wide distribution that has been reported throughout the Atlantic, Indian, western, north, central and south-eastern Pacific Oceans. In the Northern Gulf of Mexico Zameus squamulosus is occasionally captured by longlines in deep waters off the coast of Florida, but until now there were no records of the species in the Southern Gulf of Mexico. Four specimens of Zameus squamulosus were collected in 2004 and 2009 on the continental slope of the Gulf of Mexico. Collections were made at depths of 698 m and 701 m. These specimens constitute the first records of this species for the southern Gulf of Mexico and, as they were captured with bottom associated trawls, we infer that this species is more commonly found at the bottom ocean.

Biological aspects of the Gulper shark, Centrophorus granulosus (BLOCH and SCHNEIDER, 1801), from the Mediterranean coast of Israel

Article

Jan 2000

Biological aspects of the gulper shark Centrophorus granulosus were studied from September 1982 to November 1992 along the Mediterranean coast of Israel at depths of 200-1400 m. Males dominated the intermediate depths (550-800 m), while at the shallowest depths (200-400 m) the population consisted mainly of females. Gravid females had only one embryo or a single large egg. Stomach contents revealed that the diet of C. granulosus consisted mainly of cephalopods and meso- to bathypelagic fishes. The ratio of body length to the percentage of liver weight from total body weight increased from ca. 15% in small specimens to ca. 25% in large specimens. A rational fishing exploitation policy, which recommends concentrating fishery on male rich depths, is presented.

Morphometrics of neonate velvet belly, Etmopterus spinax (Linnaeus, 1758).

Article

Full-text available

Jan 2001

Alessandro De Maddalena

Barcoding deep-water chondrichthyans from mainland Portugal

Article

Full-text available

Jan 2015

Most deep-water chondrichthyans occurring off mainland Portugal are distributed worldwide. There are many closely related species with similar morphology, and the lack of diagnostic characters that unambiguously allow species discrimination has led to extensive identification problems. Here, DNA barcodes were used to evaluate the suitability of cytochrome c oxidase I (COI) to identify deep-water chondrichthyans and to further contribute to the worldwide molecular databases currently in use. The sample was composed of 40 individuals from the families Chimaeridae, Centrophoridae, Somniosidae, Etmopteridae, Oxynotidae, Dalatiidae, Scyliorhinidae, Mitsukurinidae, Chlamydoselachidae and Hexanchidae. COI proved to be adequate for species identification, with almost all putative species recovered as well supported monophyletic clades, with low intraspecific variation. Sequence matches against the BOLD database provided evidence for the existence of identification problems particularly within the genera Hydrolagus, Galeus and Centrophorus. Present results suggest that three different Centrophorus species occur off the Portuguese mainland, C. squamosus, C. granulosus and C. uyato. The sample also included an albino Deania calcea and a C. squamosus specimen without dermal denticles. This study updates the current knowledge on diversity and distribution of deep-water chondrichthyans occurring along the Portuguese coast, and provides an essential tool for species identification and consistency of taxonomic designations worldwide.

Dermal Denticles anD morphometrics of the sailfin roughshark OxynOtus paradOxus (elasmobranchii, oxynotiDae), with comments on its geographic Distribution

Article

Jun 2003
CYBIUM

The dermal denticles of the sailfin roughshark Oxynotus paradoxus are described and illustrated with SEM pictures, based on two specimens captured at the Azores. The flank denticles are similar to those of O. centrina, with a central cusp flanked by two smaller lateral cusps, rising from the lateral ridges, and a secondary median cusp posterior to the main one. Differences in squamation between both species are described. Body proportions of the Azorean specimens are given and found to be consistent with those reported by previous authors. The published information shows depth of capture to have a mode at 570 m. A bathybenthic habitat has been suggested, with spring reproductive migrations to the continental shelf. The presence of this species in the Azores and Mid-Atlantic Ridge represents a significant westward extension of its previously known geographic distribution, the continental shelf and upper slope of the north and eastern Atlantic. It is possible that O. paradoxus is continuously distributed along the north-eastern Atlantic floor, deeper than presently known. Alternatively, separate slope and ridge populations may exist.

Species diversity of the deep-water gulper sharks (Squaliformes: Centrophoridae: Centrophorus) in North Atlantic waters – current status and taxonomic issues

Article

Full-text available

Dec 2014

The gulper sharks (genus Centrophorus) are a group of deep-water benthopelagic sharks with a worldwide distribution. The alpha taxonomy of the group has historically been problematic and the number of species included in the genus has varied considerably over the years and is still under debate. Gulper sharks are routinely caught in mid- and deep-water fisheries worldwide and some have shown a considerable decline in abundance in the last few decades. Clear and consistent species discrimination of Centrophorus is essential for an efficient and sustainable management of these fisheries resources. Our study used molecular cytochrome oxidase subunit I (COI) and 16S ribosomal RNA gene sequences] and morphometric data to re-evaluate the diversity of Centrophorus in North Atlantic waters, including the Gulf of Mexico, the Caribbean, and the Mediterranean Seas. Molecular data separated North Atlantic Centrophorus into five well-supported groups whereas morphometric data separated these same five groups and suggested three additional groups for which no molecular data were available. Four of the five groups identified in the North Atlantic also occur in the Indian and/or Pacific Oceans, thus extending the reported range of some species considerably. A species identification key for North Atlantic Centrophorus is provided based on our findings.

An inventory of Bramble sharks Echinorhinus brucus (Bonnaterre, 1788) (Elasmobranchii, Echinorhinidae) in natural history collections worldwide for conservation status assessment

Article

Full-text available

Nov 2023
ZOOSYSTEMA

Many elasmobranch populations were already depleted well before fishery surveys had even started, which means historical investigations are needed to reveal their ignored declines. This is probably the case for the Bramble shark Echinorhinus brucus (Bonnaterre, 1788) whose populations in Europe are suspected of having decreased significantly. In order to document this data deficiency, an inventory of Bramble shark material that had been preserved in natural history collections, was conducted in the period 2014-2022. A total of 128 collections were contacted around the world, and additional sources of information were traced and consulted (e.g. collection labels, museum registers, digital databases, index cards, pictures, manuscripts and publications). This resulted in a list of 234 entries, subsequently assigned to 169 individual Bramble sharks. These exhibits are, or had been deposited in 80 different collections, spread over 22 countries, whereas the other 48 collections yielded no results. At least 40 entries are presumed lost, so that fewer than 200 entries have been preserved to date, some of them in bad condition. Due to their historic and scientific importance, extensive efforts to preserve these specimens are more than justified. A significant number of 64 individuals, representing more than 37% of all specimens that were recorded in this survey, have never been published, and are reported here for the first time. Associated geographical data and collection dates are present for nearly all specimens. These ‘new historical records’ can add significantly to our knowledge of the Bramble sharks’ relative abundance and geographical distribution in time. These data will be included in the ongoing Bramble shark Cold Case, a project that will document its suspected decline, and to implement appropriate conservation measures for this iconic, little-known and endangered shark species.

Overview of the Genus Squalus in the Mediterranean Sea

Chapter

Full-text available

Jan 2023

In the Mediterranean Sea, in addition to the two historically known species belonging to the Squalus genus (Squalus blainville and Squalus acanthias), a third species, Squalus megalops, has been reported. This last specie is a subject of debate between authors. S. acanthias is quite distinct from the other species of the genus Squalus, while S. blainville and S. megalops are very similar morphologically. This similarity has resulted in considerable confusion over their taxonomy. The lack of a well-preserved holotype for S. blainville, misidentifications in databases and in the literature, description, and figure of Risso (1827) not conforming to any known species of Squalus are impediments to the proper taxonomic identification and the potential revision of the genus. This chapter aims to clarify the state of the species of the genus Squalus in the Mediterranean Sea, taking into account all the studies carried out on this subject.

Nouvelle description de Centrophorus granulosus (Schneider, 1801) (Pisces, Squalidae). Données sur la biologie de la reproduction et le régime alimentaire des spécimens des côtes tunisiennes

Article

Full-text available

Apr 1985

Christian Capapé

First genetically confirmed records of the little gulper shark Centrophorus uyato (Squaliformes: Centrophoridae) from Cypriot waters

Article

Full-text available

Sep 2021

The taxonomy within the genus Centrophorus has been controversial almost since its origin, raising uncertainties about the identification, the phylogenetic placement and the geographical distribution of several species. The partial nucleotide sequences of two mitochondrial DNA gene regions, the cytochrome c oxidase subunit I and the 16S ribosomal RNA, genetically confirmed the presence of the little gulper shark in Cypriot waters. The species presence in the Mediterranean Sea is revised and discussed.

Etmopterus brosei sp. nov.: a new lanternshark (Squaliformes: Etmopteridae) from the southeastern Atlantic and southwestern Indian oceans, with a revised key to the Etmopterus lucifer clade

Article

Jun 2021

A new species of lanternshark, Etmopterus brosei sp. nov. (Squaliformes: Etmopteridae), is described from the southeastern Atlantic and southwestern Indian oceans. The new species resembles other members of the Etmopterus lucifer Jordan & Snyder, 1902 clade in having linear rows of dermal denticles, and most closely resembles the conspecific E. sculptus Ebert, Compagno, & De Vries, 2011 from the southeastern Atlantic and southwestern Indian oceans. The new species is fairly common along the upper continental slopes off South Africa, Mozambique, and seamounts along the Madagascar Ridge, including Walters Shoal, in 480–1200 m depth. It can be distinguished from other members of the E. lucifer clade by a combination of characteristics, including the arrangement of flank and caudal markings, shape and size of flank marking, the arrangement of dermal denticles along the body, and the presence of dermal denticles on the dorsal fin bases. A revised key to the Etmopterus lucifer clade is provided.

Monograph An annotated checklist of the chondrichthyans of South Africa

Article

Mar 2021

An annotated checklist of chondrichthyan fishes (sharks, batoids, and chimaeras) occurring in South African waters is presented. The checklist is the result of decades of research and on-going systematic revisions of the regional fauna. The chondrichthyan fauna of South Africa is one of the richest in the world with 191 species, comprising 50 families and 103 genera. It consists of 30 families, 64 genera, and 111 species of sharks; 17 families, 36 genera, and 72 species of batoids; and, 3 families, 5 genera, and 8 species of chimaeras. The most species-rich shark families are the whaler sharks Carcharhinidae with 20 species followed by the deepwater catsharks Pentanchidae with 13 species. The most species-rich batoid families are the hardnose stakes Rajidae with at least 21 species followed by the stingrays Dasyatidae with 13 species. This monograph represents the first detailed annotated checklist of chondrichthyans from South Africa in over 30 years.

Squalus shiraii sp. nov. (Squaliformes, Squalidae), a new species of dogfish shark from Japan with regional nominal species revisited.

Article

Full-text available

Jun 2020

A new species of deep-water dogfish shark, Squalus shiraii sp. nov., is described herein as endemic to the tropical waters off Southern Japan. This species has been largely misidentified with S. mitsukurii. However, morphological, meristic and morphometric evidence support it to be a separate and undescribed species. Squalus shiraii sp. nov. differs from this species by having body brown in colour dorsally, caudal fin with ventral and dorsal tips markedly tapered and broadly white, dermal denticles uniscuspidate and lanceolate and larger number of precaudal (91-94) and total vertebrae (120-123) (vs. body dark grey to black; caudal fin with ventral and dorsal tips rounded and not white in colour; denticles tricuspidate and rhomboid; 86-90 precaudal and 116-117 total vertebrae). Squalus shiraii sp. nov. is also clearly separated from other Japanese congeners which are herein revisited to include six species, based on the examination of over 150 specimens caught from Japanese waters that were available in ichthyological collections: S. mitsukurii, S. japonicus, S. acutirostris, S. brevirostris and S. suckleyi. Squalus mitsukurii, S. japonicus and S. brevirostris are re-described in detail and the neotype of S. japonicus is herein designated. Squalus acutirostris is treated as a valid species with occurrences in Japan, China and Taiwan and, thus, a provisional diagnosis is given, as well as an updated diagnosis of S. suckleyi. A key to Squalus species from the Northwestern Pacific Ocean is given and main morphological differences between S. shiraii sp. nov. and the closest related species are discussed.

Squalus shiraii sp. nov. (Squaliformes, Squalidae), a new species of dogfish shark from Japan with regional nominal species revisited

Article

Full-text available

Jun 2020
Mitt Mus Natur Be Zool Reihe

A new species of deep-water dogfish shark, Squalus shiraii sp. nov., is described herein as endemic to the tropical waters off Southern Japan. This species has been largely misidentified with S. mitsukurii. However, morphological, meristic and morphometric evidence support it to be a separate and undescribed species. Squalus shiraii sp. nov. differs from this species by having body brown in colour dorsally, caudal fin with ventral and dorsal tips markedly tapered and broadly white, dermal denticles uniscuspidate and lanceolate and larger number of precaudal (91-94) and total vertebrae (120-123) (vs. body dark grey to black; caudal fin with ventral and dorsal tips rounded and not white in colour; denticles tricuspidate and rhomboid; 86-90 precaudal and 116-117 total vertebrae). Squalus shiraii sp. nov. is also clearly separated from other Japanese congeners which are herein revisited to include six species, based on the examination of over 150 specimens caught from Japanese waters that were available in ichthyological collections: S. mitsukurii, S. japonicus, S. acutirostris, S. brevirostris and S. suckleyi. Squalus mitsukurii, S. japonicus and S. brevirostris are re-described in detail and the neotype of S. japonicus is herein designated. Squalus acutirostris is treated as a valid species with occurrences in Japan, China and Taiwan and, thus, a provisional diagnosis is given, as well as an updated diagnosis of S. suckleyi. A key to Squalus species from the Northwestern Pacific Ocean is given and main morphological differences between S. shiraii sp. nov. and the closest related species are discussed.

Clasper Morphology of the Japanese Sawshark, Pristiophorus japonicus Günther, 1870 (Chondrichthyes: Elasmobranchii)

Article

Full-text available

Feb 2019
ANAT REC

Sawsharks (Pristiophoriformes) are slender, medium‐sized sharks with elongated, saw‐like snouts, and include the monotypic Pliotrema and Pristiophorus with seven species. The phylogenetic position of sawsharks is still problematic as phylogenetic hypotheses based on morphological and molecular evidence disagree about their relationships, whether closer to batoids (morphological data) or grouped with squaliforms, angelsharks, and hexanchiforms in an all shark higher taxon (molecular data). However, many aspects of the morphology of sawsharks are poorly known. The present article describes the clasper musculature and skeleton of a sawshark (Pristiophorus japonicus); the clasper skeleton of a sawshark is described for the first time. The clasper musculature is similar to squaliforms and most batoids, whereas the clasper skeleton is similar to that found in Squatina and Squalus. However, the ventral marginal, dorsal terminal (dt), and ventral terminal cartilages are distinct and diagnostic at least for Pristiophorus japonicus. Comparisons with galeomorph sharks are necessary to further refine our conclusions in relation to the systematic significance of the clasper muscles and skeleton of the Japanese sawshark. Anat Rec, 302:1666–1670, 2019. © 2019 American Association for Anatomy

Comparative morphology and systematics of the cookiecutter sharks, genus Isistius Gill (1864) (Chondrichthyes: Squaliformes: Dalatiidae)

Article

Full-text available

Aug 2018
PLOS ONE

The dalatiid genus Isistius Gill (1864) has three valid species currently recognized in the literature: Isistius brasiliensis Quoy & Gaimard (1824), I. plutodus Garrick & Springer (1964), and I. labialis Meng, Zhu & Li (1985). The most common species, I. brasiliensis, has a wide geographic distribution and is found in subtemperate and tropical seas circumglobally. A comparative analysis of specimens from different localities throughout its range, however, had never been undertaken. In the present paper, the morphological variation of this species along its entire distribution has been thoroughly analyzed, corroborating that it represents a single widespread species and that I. labialis is its junior synonym. The other congeneric species, I. plutodus, is known from only a few specimens and is also distributed worldwide. A detailed comparative analysis of available material of I. plutodus was conducted verifying its validity as a single widespread species. The present study analyzed in detail the external morphology (coloration, dentition, dermal denticles), internal morphology (skeleton, musculature), lateral-line canals, and morphometric and meristic characters of species of Isistius in order to better define the genus and its included valid species.

Investigation on the genus Squalus in the Sardinian waters (Central-Western Mediterranean) with implications on its management

Article

Jun 2018

In the Mediterranean Sea, in addition to the two historically known species belonging to the Squalus genus, a third species, Squalus megalops, has been reported. Considering the high level of morphologic similarity of this species with the native species S. blainville, this study aims to evaluate the Central-Western Mediterranean spurdog population in order to test the hypothesis of the presence of two distinct species S. blainville and S. megalops. A total of 137 spurdogs, caught in the Sardinian waters, were analyzed morphologically and genetically after their subdivision into two groups depending on the number of the lateral processes in the chondrocranium basal plate. The CAP analysis, employing all body and chondrocranial measurements, revealed no clear segregation among the a priori assigned groups with a high misclassification percentage. Besides, no evident dissimilarities in teeth and dermal denticle morphology between the two groups were observed. All the 18 specimens which were genetically analyzed, by sequencing of the mtDNA marker COI, clustered together resulting to be S. blainville. All the obtained results indicated the presence, in the study area, of only one species, ascribable to S. blainville.

Two new species of short-snouted dogfish sharks of the genus Squalus Linnaeus, 1758, from southern Africa (Chondrichthyes: Squaliformes: Squalidae)

Article

Apr 2017

Species composition of the genus Squalus from the Eastern Atlantic and Western Indian Oceans is still poorly known with three to four species often recognized: S. acanthias, S. megalops, S. blainvillei and S. mitsukurii. A fifth species, S. acutipinnis, was recently redescribed as valid in the region, although morphological variation was noticed among its type specimens that indicates the presence of two different forms. The second form is herein described as Squalus margaretsmithae sp. nov. and distinguished from S. acutipinnis based on external morphological characters. Squalus mahia sp. nov. is also described from Southern Africa based on material mostly collected from Madagascar. Squalus mahia sp. nov. stands out from other Squalus species by having a conspicuously slender body, elongate and thin dorsal-fin spines, narrow caudal fin, and other external proportions. These two species are often misidentified with the Australian S. megalops because they share a short snout, white postventral caudal margins, lanceolate and unicuspid dermal denticles, and low number of vertebrae. Comparative analyses between Squalus margaretsmithae sp. nov., Squalus mahia sp. nov. and morphologically similar species that also share these features, including S. brevirostris, S. crassispinus, S. acutipinnis, S. altipinnis, and S. hemipinnis are provided. A taxonomic evaluation of the nominal species S. megalops and its occurrence in the region is also discussed.

Taxonomy and morphology of species of the genus Squalus Linnaeus, 1758 from the Southwestern Atlantic Ocean (Chondrichthyes: Squaliformes: Squalidae)

Article

Jul 2016
ZOOTAXA

Squalus is a genus of reportedly cosmopolitan shark species that have a high taxonomic complexity due to difficulties in their morphological differentiation; many of its species need revision. Currently, there are 26 valid species of Squalus, which have been divided into three species-groups according to overall morphological similarity, the S. acanthias, S. megalops, and S. mitsukurii groups. Loss of type specimens, propagation of erroneous identifications in the literature, and difficulties in obtaining representative series for comparison are secondary challenges that have impeded a global taxonomic revision of the genus. This problem applies clearly to species from the Southwestern Atlantic Ocean, including species that occur off Brazil. Following a current global tendency, a regional taxonomic revision of Squalus was conducted in order to investigate which species are valid in the Southwestern Atlantic Ocean and provide diagnostic morphological characters that can be efficiently used for identifying species. Comparative detailed analysis of external (e.g. morphometrics, dentition, and color pattern) and skeletal morphology (primarily meristic data, neurocrania and claspers) of specimens of Squalus from the region revealed four new species that are herein described (S. albicaudus sp. nov., S. bahiensis sp. nov., S. lobularis sp. nov., and S. quasimodo sp. nov.), as well as S. acanthias, which is redescribed from the region based on new material. Comparisons are offered based on examinations of congeneric species; this work is part of a global systematic revision of Squalus.

Redescription of Squalus acutipinnis Regan, 1908, a Valid Species of Spiny Dogfish from Southern Africa (Chondrichthyes: Squaliformes: Squalidae)

Article

Jun 2016

The Bluntnose spiny dogfish Squalus acutipinnis Regan, 1908 is redescribed based on the re-examination of its type specimens and non-type material from Southern Africa. The taxonomic confusion concerning its validity is mainly related to its heterogeneous type series. Its taxonomic status is clarified as a valid species endemic to the Southwestern Indian Ocean when compared to congeners from the region and other valid species with which it has been placed in synonymy. Squalus acutipinnis can be distinguished from all species of the "megalops-cubensis group" by fewer total, precaudal, and monospondylous vertebrae (except from Squalus megalops, Squalus brevirostris, and Squalus crassispinus). Squalus acutipinnis is clearly distinct from Squalus megalops from Southern Australia and the Japanese S. brevirostris through characters of pectoral fin and external measurements. The South African species differs from S. crassispinus by having more slender first and second dorsal-fin spines. Squalus acutipinnis is also easily distinguished from the regional congeners S. acanthias, S. blainvillei, and S. mitsukurii by having lanceolate dermal denticles (vs. non-lanceolate unicuspid denticles in S. acanthias, and non-lanceolate tricuspid denticles in S. blainvillei and S. mitsukurii). © 2016 by the American Society of Ichthyologists and Herpetologists.

Checklist of sharks, rays and chimaeras (Chondrichthyes, Elasmobranchii, Holocephali) from Mexico

Article

Full-text available

Apr 2016

We present an annotated checklist of the species of sharks, rays and chimaeras (chondrichthyan fishes) occurring in Mexican waters, based on a thorough review of the literature and electronic database searches, examination of museum collection specimens, and unpublished records obtained during fieldwork conducted in the last four years. The checklist contains information of at least 214 species of chondrichthyan fishes that occur in Mexican marine and brackish waters, assigned to 84 genera, 40 families and 14 orders. It includes eight species of chimaeras, 95 batoids and 111 sharks. Condrichthyan fauna in Mexico is one of the richest in the world, with almost 17.3% of the known species. An additional 16 species are included as their occurrence in Mexican marine waters is probable according to distributional patterns.

A new bathyal shark fauna from the Pleistocene sediments of Fiumefreddo (Sicily, Italy)

Article

Jun 2007

Stefano Marsili

A new shark fauna is described from the lower-middle Pleistocene marine sediments outcropping near the Fiumefreddo village, Southern Italy. The fossil assemblage mostly consists of teeth belonging to the bathydemersal and bathypelagic elasmobranch species Chlamydoselachus anguineus, Apristurus sp., Galeus cf. melastomus, Etmopterus sp., Centroscymnus cf. crepidater, Scymnodon cf. ringens, Centrophorus cf. granulosus and C. cf. squamosus, commonly recorded along the extant outer continental shelf and upper slope. From a bathymetrical point of view, the present vertical distribution of the taxa collected allows an estimate of a depth between 500 and 1000 m. The bathyal character of the fauna provides new evidence of a highly diversified and heterogeneous deep-sea Mediterranean Plio-Pleistocene marine fauna, in response to the climatic and hydrographical changes. Finally, the Fiumefreddo fauna provides new relevant data for the understanding of the processes involved in the evolution of the extant Mediterranean selachian fauna. © Publications Scientifiques du Muséum national d'Histoire naturelle.

Somniosus rostratus. The IUCN Red List of Threatened Species 2009

Article

Full-text available

Jan 2009

Redescription of Scymnodon ichiharai Yano and Tanaka 1984 (Squaliformes: Somniosidae) from the western North Pacific with comments on the definition of somniosid genera

Article

Full-text available

Oct 2014
ICHTHYOL RES

The somniosid species Scymnodon ichiharai Yano and Tanaka 1984 is redescribed based on the type specimens and additional material from Taiwan and Japan. The range of this species is extended to include Taiwanese waters. Although recently allocated to the genus Zameus, this species is very similar to Scymnodon plunketi from the southern Indo-West Pacific; our molecular evidence indicates that these species are sister-taxa. The genus Proscymnodon Fowler 1934 is placed in the synonymy of Scymnodon Barboza du Bocage and de Brito Capello 1864 and new generic definitions are provided for Scymnodon and the closely related Zameus. The genus Scymnodon is considered to include at least the species S. ichiharai, S. plunketi, and S. ringens; Proscymnodon macracanthus (Regan 1906) is allocated to Scymnodon, but its validity is uncertain. The genus Zameus is considered to be monotypic, containing only the species Z. squamulosus.

A study of the sharks of the suborder Squaloidea

No full-text available

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