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Redescription of Hexanchus nakamurai Teng 1962 (Chondrichthyes: Hexanchiformes: Hexanchidae), with designation of a neotyp
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Hexanchus nakamurai Teng, 1962 is one of two valid nominal species in the genus Hexanchus; the other being H. griseus. The taxonomic history of H. nakamurai is somewhat convoluted due to questions about the validity of whether it constituted a publication or an unpublished dissertation. The issue appeared to have been resolved once it was determined that the Teng's original description met the criteria under the International Commission on Zoological Nomenclature code (Article 8a) of a publication. However, recent molecular studies have indicated that the western North Atlantic H. nakamurai (= ? H. vitulus) may be distinct from western Indian Ocean H. nakamurai. Compounding the issue is the loss of the holotype of H. nakamurai from Taiwan. A neotype is herein designated and the species redescribed based on the neotype and eight additional Taiwanese specimens.
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... These specimens were deposited and cataloged in the ichthyology collection at El Colegio de la Frontera Sur (ECOSC). The specimens were identified following the relevant literature [2,[5][6][7][8][9][10][11]. Additionally, biometrics were recorded for each specimen which follow to Ebert et al. [9] and Heemstra [10] with some modifications and additions based on the morphology of the organisms examined ( Table 1). ...
... The specimens were identified following the relevant literature [2,[5][6][7][8][9][10][11]. Additionally, biometrics were recorded for each specimen which follow to Ebert et al. [9] and Heemstra [10] with some modifications and additions based on the morphology of the organisms examined ( Table 1). The nomenclature and taxonomic arrangement are after Page et al. [12]. ...
... We identified a total of 2 genera corresponding to an equal number of families and orders, which were described as follows: The genus Mustelus includes 27 species distributed in tropical, subtropical, and temperate climates of the world's oceans [5,7,8,9], representing 33.3% of the species in Mexican waters [2,13]. Mustelus sinusmexicanus Heemstra, 1997( Figure 1, Table 1). ...
... The Atlantic sixgill shark Hexanchus vitulus Springer & Waller, 1969 is one of the three species of the genus Hexanchus, along with the bluntnose sixgill shark H. griseus (Bonnaterre, 1788) and the bigeye sixgill shark H. nakamurai Teng, 1962(Compagno et al., 2005Daly-Engel et al., 2019). In previous decades, both H. nakamurai and H. vitulus were recognized as the same species; however, recent genetic studies have suggested the divergence between both taxa (Ebert et al., 2013;Daly-Engel et al., 2019). In the Caribbean Sea, the knowledge of H. vitulus and other deep-sea sharks is scarce, as these species were infrequently captured by local artisanal fishers, and therefore scientific research regarding its biology has not been developed (Hacohen-Domené et al., 2016 (Ehemann et al., 2019), and the Dutch Caribbean (Van Beek et al., 2012), there is no information about its presence in Guatemalan waters or its morphometry in any locality of the Caribbean Sea. ...
The present study constitutes the first records and morphometry of Hexanchus vitulus on the Caribbean coast of Guatemala. A total of 10 Atlantic six-gill sharks were captured by artisanal fishers during 2015-2019, showing a sex ratio of 2.3:1 (males:females) and a total length that ranges 61-165 cm. Morphometric measurements are provided for future comparisons in other coastal regions. Recorded sharks corresponded mostly to sexually mature individuals, which differs from that reported for different areas of the Caribbean.
Using all data sources available, we collected 2,189 nominal scientific names that have been applied to the fishes from Gabon. Data from the literature and online database indicate that 1,062 valid species of fishes live in Gabonese waters, with 288 of these strictly restricted to freshwaters, 592 strictly restricted to marine environments and 182 species euryhaline species. Among the latter one finds 121 species inhabit in both marine and brackish environments, 16 that occur in both freshwater and brackish environments and 45 found in all salinities. these 1,062 species represent 60 orders and 224 families. an additional 202 species, mostly marine, may be present in Gabon although they have not been yet recorded. endemic species represent 7% (75) of the 1,062 valid described species for Gabon, within just one of these from marine waters and 74 freshwaters spe- cies (mostly killifish within the genus Aphyosemion – 33 species). regarding the iuCn status, 135 present (+19 possible) species (12.7%) are considered as endangered (from near threatened to critically endangered), and 135 (+24 possible) (12.7%) species are not evaluated or data deficient. The remaining species are least concern. Continued descriptions of new species from the waters of Gabon demonstrate that the present total most likely underestimates the species level diversity of the fish fauna.
Elasmobranchii are relatively well-studied. However, numerous phylogenetic uncertainties about their relationships remain. Here, we revisit the phylogenetic evidence based on a detailed morphological re-evaluation of all the major extant batomorph clades (skates and rays), including several holomorphic fossil taxa from the Palaeozoic, Mesozoic and Cenozoic, and an extensive out-group sampling, which includes sharks, chimaeras and several other fossil chondrichthyans. The parsimony and maximum-likelihood analyses found more resolved but contrasting topologies, with the Bayesian inference tree neither supporting nor disfavouring any of them. Overall, the analyses result in similar clade compositions and topologies, with the Jurassic batomorphs forming the sister clade to all the other batomorphs, whilst all the Cretaceous batomorphs are nested within the remaining main clades. The disparate arrangements recovered under the different criteria suggest that a detailed study of Jurassic taxa is of utmost importance to present a more consistent topology in the deeper nodes, as issues continue to be present when analysing those clades previously recognized only by molecular analyses (e.g., Rhinopristiformes and Torpediniformes). The consistent placement of fossil taxa within specific groups by the different phylogenetic criteria is promising and indicates that the inclusion of more fossil taxa in the present matrix will likely not cause loss of resolution, therefore suggesting that a strong phylogenetic signal can be recovered from fossil taxa.
Shark skin is covered by small structures called dermal denticles whose functions are diverse, such as protection, bioluminescence, hydrodynamics, among other functions. These structures have a great variety of shapes and sizes, which can be a useful approach for specimen identification as diagnostic characters between species. The present study aims to describe the dermal denticles morphology of the broadnose seven-gill shark Notorynchus cepedianus, evaluating differences among life-stage (neonate, juvenile and adult), sex and body region (dorsal and ventral). For achieving it, 39 specimens were collected at six landing points along the Peruvian coast. The dermal denticles from two body regions
(dorsal and ventral) were photographed, measured (length, width, angle and density), and described using a stereoscope. Dermal denticles measures showed significant morphological differences between body regions as well as stages of development, but not between sexes. The differences are: (1) Crown shape: as the individual grows, it can be seen that the cross shape is losing, (2) Crown cusps: cusps length varied according to the stage of each individual, it was also observed that the lateral cusps are larger in dorsal than ventral region, and (3) Union peduncle - crown: adult specimens and both body regions, the observed union was very dimly and it did not have a defined shape. On the whole, these reported variations in measured traits could be useful as diagnostic characters to identify the stage of development at which the landed and marketed specimens are found.
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.
Hexanchus nakamurai is a deep‐water species, with very little scientific information. This study confirms the distribution of the species in the most eastern region of the Mediterranean Sea, Levantine Sea, in addition to providing some biological information from four pregnant individuals, which is being reported for the first time in the Mediterranean Sea. A total of four individuals were bycaught, in two sets on opposite coasts, three on the 13th of May 2020 from the western coast, and an individual on the 14th June 2020 from east coast of the island of Cyprus. The four specimens, all pregnant females, measured between 107 and 116 cm in total length and between 4,330 and 4,960 g in weight. All specimens were in early pregnancy according to the level of embryo development, which confirms that the size at maturity is smaller than previously reported. In the stomachs, remains of the hake Merluccius merluccius, the cephalopod Loligo vulgaris and two unidentified species of Hirudinea (Annelida) were found. This study provides important new information on the Mediterranean distribution of a globally rare and data deficient species, including an expansion of its known range, dietary preferences and insights of its reproduction biology; the first pregnant females reported in the Mediterranean Sea.
The sixgill sharks of the genus Hexanchus (Hexanchiformes, Hexanchidae) are large, rarely encountered deep-sea sharks, thought to comprise just two species: the bluntnose sixgill Hexanchus griseus (Bonaterre, 1788) and the bigeye sixgill Hexanchus nakamurai (Teng, 1962). Their distribution is putatively worldwide in tropical and temperate waters, but many verified records for these species are lacking, and misidentification is common. Taxonomic uncertainty has long surrounded H. nakamurai in particular, with debate as to whether individuals from the Atlantic constitute a separate species. Using 1,310 base pairs of two mitochondrial genes, COI and ND2, we confirm that bigeye sixgill sharks from the Atlantic Ocean (Belize, Gulf of Mexico, and Bahamas) diverge from those in the Pacific and Indian Oceans (Japan, La Reunion, and Madagascar) with 7.037% sequence divergence. This difference is similar to the genetic distance between both Atlantic and Indo-Pacific bigeye sixgill sharks and the bluntnose sixgill shark (7.965% and 8.200%, respectively), and between the entire genus Hexanchus and its sister genus Heptranchias (8.308%). Such variation far exceeds previous measures of species-level genetic divergence in elasmobranchs, even among slowly-evolving deep-water taxa. Given the high degree of morphological similarity within Hexanchus, and the fact that cryptic diversity is common even among frequently observed shark species, we conclude that these results support the resurrection of the name Hexanchus vitulus Springer and Waller, 1969 for bigeye sixgill sharks in the northwest Atlantic Ocean. We propose the common name “Atlantic sixgill shark” for H. vitulus, and provide new locality records from Belize, as well as comments on its overall distribution.
After Randall & Lim (2000) compiled a checklist of 3,365 species of marine fi shes from the South China Sea (SCS), it was expected that there would be an increase of many new species or new records, especially the deep-sea fi shes, in this region. In this paper, we went through the Fish Database of Taiwan and sorted a total of 38 orders, 230 families and 2,133 species that occurred in the southwestern Taiwan waters and SCS and have either voucher specimen, underwater photos or citations. Among them, 128 species belonging to 72 families are new records from Taiwan. In the checklist, 171 species occurred only in SCS, including 42 species only in Pratas Islands, 25 species only in Spratly Islands and 81 in other SCS areas; and 1,473 species occurred only in the southwestern inshore habitats of Taiwan. There are 317 new record species that were not included in the checklist of Randall & Lim (2000) and 45 species that are new addition to the fi sh fauna of SCS.
An annotated checklist of fish genera and species described from Taiwanese waters through 2009 is presented. It includes 20 genera and 336 species/subspecies in 99 families. Of these, 225 species/subspecies are currently recognized as valid and 111 are invalid, including 7 questionable species. The current status of each taxon, if different from that of the original description, is provided. Thus far, 41 primary freshwater and estuarine species/subspecies are considered as endemic and 55 marine species are found only around Taiwan. The type series collected from Taiwan are also listed based on the information provided in the original descriptions and from our investigation. It includes approximately 2217 specimens in 779 lots, including 242 holotypes and lectotypes, 5 neotypes, 35 lots of syntypes and 497 lots of paratypes and paralectotypes. There are still 19 species lacking primary types and 11 lots with at least 31 unknown secondary type specimens.
Part B of this series, the Batomorphii is continued with the description and illustration of the tooth morphology (SEM-photographs) with additional information about the tooth vascularisation of the order Torpediniformes. Differential diagnosis and a classification of the torpediniform taxa from the odontological point of view are also presented. It closes the entire series on sharks, rays and skates and holocephalans after 16 years. The authors and editor are planning to enhance the contents of the series with the publication of additional short notices including their personal reflections on the systematics of the whole group concerned. Key words: Elasmobranchii - Batomorphii - Torpediniformes Odontology.