Precaudal Vertebrae Research Articles

Precaudal Vertebrae in the Postcranial Region of Moray Eels Form Ventral Processes.

Fish vertebrae are primarily morphologically classified into precaudal vertebrae jointed to the ribs and caudal vertebrae with hemal spines, through which the caudal artery and veins pass. Moray eels (family Muraenidae) capture prey by directly biting, combining oral and pharyngeal jaw. During feeding motions, they exhibit various head manipulations, such as neurocranial elevation, ventral flexion, and horizontal shaking, with their postcranial region acting like the neck of amniotes. However, the bone morphology supporting these movements remains unclear. In this study, the vertebral morphologies of the Kidako moray (Gymnothorax kidako), starry moray (Echidna nebulosa), pink-lipped moray (Echidna rhodochilus), tidepool snake moray (Uropterygius micropterus), and Seychelles moray (Anarchias seychellensis) were investigated using X-ray computed tomography. These five species exhibited longitudinal ventral processes in the second to approximately 12th precaudal vertebrae with canals for blood vessels, structurally similar to hemal spines. In addition, the morphology of the precaudal vertebrae in three Anguilliformes species closely related to moray eels and two Gasterosteiformes species, including a seahorse that flexes its head ventrally as a feeding motion, was compared with that of moray eels. However, no remarkable ventral processes were observed in their precaudal vertebrae in the postcranial region, suggesting that these structural features in the postcranial vertebrae were preserved in Muraenidae but not necessarily required for the fish to bend its head ventrally. Although the functional significance of the ventral process has yet to be determined, our findings highlight a novel aspect of fish vertebral morphology.

Descriptive Osteology of Catfish, Sperata aorides (Jerdon, 1849) of the Bagridae Family from Cauvery River Basin, Tamil Nadu, India

The descriptive and comparative osteological analysis was conducted on Bagridae catfish S. aorides based on the specimens collected from the Cauvery River Basin in Tamil Nadu. S. aorides with a supraoccipital spine that is equal to or longer than the inter-neural shield with 26 pre-caudal vertebrae and has the first dorsal fin pterygiophores that are externally visible and united anteriorly rather than being distinct. The supra-occipital spine had the same width from base to tip with a broader base. The groves in the skull serve as the primary osteological indicator and serve as the morphological marker. The neuron cranium, upper and lower jaws, pectoral and pelvic girdles, and the vertebral column were among the bones whose structures were described based on the findings.

Patterns of Phenetic Diversity and Taxonomy of the Ide <i>Leuciscus idus</i> (Cypriniformes, Cyprinidae) from Water Bodies of Russia and Adjacent Countries

Using the methods of population morphology, we studied the structure of phenetic diversity of the ide Leuciscus idus (L.) from the water bodies of the Russian Federation and some neighboring countries. We analysed our own collection and literature data on meristic characters of external morphology, axial skeleton, as well as the pharyngeal teeth formula. The main features contributing to population differentiation were the number of lateral line scales, total vertebrae count, caudal and pre-caudal vertebrae ratio. It was shown that the strong positive relationships of the first two features with the geographical latitude of fish habitats is associated, first of all, not with the direct influence of physical factors functionally dependent on latitude, but with particular (sub)speciation processes in river basins and dispersal of evolutionarily derived forms to the north. The results obtained are discussed in terms of evolutionary trends in the subfamily Leuciscinae and call for a taxonomic revision of the L. idus species in its current volume with elevation of the former subspecies L. idus oxianus to a species rank.

Evolution of vertebral numbers in primates, with a focus on hominoids and the last common ancestor of hominins and panins

The primate vertebral column has been extensively studied, with a particular focus on hominoid primates and the last common ancestor of humans and chimpanzees. The number of vertebrae in hominoids—up to and including the last common ancestor of humans and chimpanzees—is subject to considerable debate. However, few formal ancestral state reconstructions exist, and none include a broad sample of primates or account for the correlated evolution of the vertebral column. Here, we conduct an ancestral state reconstruction using a model of evolution that accounts for both homeotic (changes of one type of vertebra to another) and meristic (addition or loss of a vertebra) changes. Our results suggest that ancestral primates were characterized by 29 precaudal vertebrae, with the most common formula being seven cervical, 13 thoracic, six lumbar, and three sacral vertebrae. Extant hominoids evolved tail loss and a reduced lumbar column via sacralization (homeotic transition at the last lumbar vertebra). Our results also indicate that the ancestral hylobatid had seven cervical, 13 thoracic, five lumbar, and four sacral vertebrae, and the ancestral hominid had seven cervical, 13 thoracic, four lumbar, and five sacral vertebrae. The last common ancestor of humans and chimpanzees likely either retained this ancestral hominid formula or was characterized by an additional sacral vertebra, possibly acquired through a homeotic shift at the sacrococcygeal border. Our results support the ‘short-back’ model of hominin vertebral evolution, which postulates that hominins evolved from an ancestor with an African ape–like numerical composition of the vertebral column.

A New Species of Sternopygus (Gymnotiformes: Sternopygidae) from the Atlantic Coast of the Guiana Shield

Sternopygus sabaji, new species, is described from the Atlantic drainages of the Guiana Shield region of South America using traditional methods of morphometrics and meristics and microcomputed tomography (µCT) scans for osteological analysis. The new species is diagnosed from all other species of Sternopygus by the lack of dentition on the anteroventral surface of the endopterygoid and by the possession of a wider mouth. It further differs from its congeners by the following combination of characters: reduced humeral spot with low-contrast and poorly defined margins, possession of a light-colored mid-lateral stripe along posterior portion of lateral line, possession of 1–3 dark saddle-like markings along dorsum of smaller individuals, and a relatively low precaudal vertebrae count. This work provides the first description of a species of Sternopygus that is endemic to the Guiana Shield, joining S. astrabes and S. macrurus in elevating the species richness of the clade in that region to three species and the total number of valid Sternopygus to ten species.

Postcranial skeletal pneumaticity in non-aquatic neoavians: Insights from accipitrimorphae.

Postcranial skeletal pneumaticity, air-filled bones of the trunk and limbs, is exclusive to birds among extant tetrapods and exhibits significant variation in its expression among different species. Such variation is not random but exhibits relationships with both body mass and locomotor specializations. Most species-level comparative research to date has focused on aquatic-oriented taxa (e.g., Anseriformes). The lack of data from non-aquatic birds constrains our ability to characterize global (i.e., avian-wide) patterns of this trait complex. To address this gap, the study conducted herein quantified postcranial pneumaticity in Accipitrimorphae, a mostly terrestrial clade composed of species that span a range of body sizes and exhibit diverse flight/foraging behaviors. All examined species (n=88) invariably pneumatized the postaxial through pre-caudal vertebrae, sternum, coracoid, humerus, vertebral and sternal ribs, and pelvic girdle, a pattern herein referred to as the accipitrimorph baseline. Of the 88 sampled species, 41 expanded upon this pattern, whereas 10 species exhibited a reduction. No species deviated from the accipitrimorph baseline by more than two anatomical regions. A phylogenetically-informed regression analysis failed to identify a significant relationship between body mass and pneumaticity. However, specific pneumaticity phenotypes deviating from the baseline were correlated with aspects of wing morphology, tail length, and home range size. Results from this and previous studies provide clarity on two hypotheses: (1) aquatic taxa display distinct pneumaticity expression patterns relative to non-aquatic birds, notably with reductions in the proportion of the skeleton filled with air in diving specialists and (2) contemporary comparative studies, including the one herein, that explicitly account for phylogenetic relationships consistently fail to support the oft-cited positive relationship between pneumaticity and body mass. Instead, historical relationships and functional/ecological attributes (e.g., diving, specialized flight behaviors) appear to be the primary drivers underlying patterns of variation in this trait complex.

Mosaic adaptive peak shifts underlie body shape diversification in pelagiarian fishes (Acanthomorpha: Percomorpha)

Abstract Extreme body elongation in fishes is a major evolutionary transformation that extends the boundaries of morphological diversity and alters aspects of function, behaviour and ecology. Prior studies have identified features of the cranial and axial skeleton that characterize elongate fishes, but a lack of detailed reconstructions of anatomical evolution has limited inferences about factors that underlie major shifts in body shape. In this study, we fitted multi-peak adaptive (Ornstein–Uhlenbeck) evolutionary models to species body shape and anatomical dimensions in Pelagiaria, a radiation of open-ocean fishes whose species span a continuum from deep bodied to highly elongate. We inferred an ancestral fusiform adaptive peak that is retained by several major pelagiarian lineages (e.g. Scombridae) and found robust support for multiple transitions to deep-bodied optima (in the families Stromateidae, Bramidae and Caristiidae) and elongate-bodied optima (within Trichiuroidei), including two instances of sequential shifts towards increasingly elongate optima that followed distinct paths of anatomical evolution. Within Trichiuridae, initial increases in head length and the number of vertebrae were followed by changes in head and vertebral shape. Within an elongate-bodied subclade of taxa traditionally identified as ‘gempylids’, changes in head and vertebral shape and in the number of precaudal vertebrae preceded an increase in the number of caudal vertebrae. Altogether, this mosaic of anatomical peak shifts suggests that body shape transformations were associated with differing selective demands and developmental changes.

X-Ray Radiological Study for Skeleton of Rounded Fantail Stingray Taeniura grabata from Susah, Libya

A sample of Round Fantail Stingray Taeniura grabata was brought, from Susah harbor in east Libya, to establish radiographically, it was situated Dorsal-ventrally, to diagnose skeleton and tooth plate, using Siemens X-ray System (Multix Fusion). In the Multi-graded radiograph, the specimen skeleton was so pale white in most of the axial skeleton and parts of the cranium, and poorly calcified. 88 pectoral radials: 41 propterygials, 15 mesopterygial, and 32 metapterygial radials, with 22 pelvic radials counted. Fin radials were attached to the scapulocoracoid by three enlarged basal radials. The superficial muscles were darker in coloration. About 80 Pre-sting vertebrae, 50 Post-sting with 62 pre-caudal vertebrae, were collected into 192 vertebrae in the tail. There were 32 upper teeth rows, and 36 lower teeth rows, they were small, blunt, and arranged into flattened surfaces. The neurocranium is slightly elongated, longer than 1.5 times in width. Nasal capsules process about 30% of neuro-cranial desk length. Meckel’s cartilages were broadly triangular. The bronchial skeleton comprises five arches. Also, a single small bridge projects ventrally from the medial plate. Jaws are very robust and small.

Age and Growth of the Spot-Tail Shark, Carcharhinus sorrah, in the Taiwan Strait

The age and growth of the spot-tail shark, Carcharhinus sorrah, were estimated based on 327 specimens (171 females and 156 males) captured by the coastal/offshore longline or drift net fishery in the waters of the Taiwan Strait from October 2010 to December 2011 and July 2019 to August 2021. Sex-specific whole weight (W)—curved total length (TL) relationships were estimated as follows: W = 7.0 × 10−6 TL2.9313 (n = 171, and p < 0.05) for females, and W = 4.0 × 10−6 TL3.0516 (n = 156, and p < 0.05) for males. The periodicity of growth band pair (including translucent and opaque bands) deposition in precaudal vertebrae was assumed to be 1 year based on centrum edge analysis and verified by a statistical analysis. The band pairs after the birth mark were counted as 0–5 and 0–8 for females and males, respectively. The Gompertz and von Bertalanffy growth function best described the observed length-at-age data for females and males, respectively. The parameters for sex-specific growth equations were estimated as: L∞ = 158.6 ± 9.09 cm TL, kG = 0.2347 ± 0.0245 year−1, and c = −0.3233 ± 0.2043 (n = 171, and p < 0.01) for females, and L∞ = 170.2 ± 9.51 cm TL, k = 0.1461 ± 0.0182 year−1, and t0 = −3.1586 ± 0.2065 (n = 156, and p < 0.01) for males.

A new species of the congrid eel genus Ariosoma (Anguilliformes: Congridae) from the south-west coast of India.

A new congrid eel species, Ariosoma maurostigma sp. nov., is described on the basis of 24 specimens collected from the deep-sea trawl by-catch, Kalamukku Fishing Harbour, off Kerala, Arabian Sea. The new species differs from all other congeners in having the following combination of characters: dark mark or spot on the posterodorsal margin of the eyes; dorsal surface of head with two faint darkish bands across the anterior and posterior margin of the eye; origin of the dorsal fin before the pectoral-fin base; short vomerine teeth patch, ST pores 3, 1 median pore and 1 lateral pore on each side just behind the median pore; preanal vertebrae 47-51; precaudal vertebrae 54-57; total vertebrae 136-142; total pores 129-134. The phylogenetic analysis reveals that the new species is closely related to Ariosoma melanospilos and Ariosoma anale, with divergences of 13.8% and 14.9%, respectively.

Description of three new species of Eigenmannia (Gymnotiformes: Sternopygidae) from the rio Mearim and rio Parnaíba basins, Northeastern Brazil

Abstract Three new species of Eigenmannia belonging to the E. trilineata species-group are described. The first species is described from rio Mearim basin and can be diagnosed by lateral line stripe restricted to last two thirds of body, superior midlateral stripe present, 176–205 anal-fin rays, 10–15 scales rows above lateral line, 109–125 lateral line scales, 19–23 premaxillary teeth, 20–29 dentary teeth, 6–10 endopterygoid teeth, and 13–14 precaudal vertebrae. The second species is described from upper rio Parnaíba, and can be diagnosed by lateral line stripe restricted to last two-thirds of body, ii,11–13 pectoral-fin rays, 180–196 anal-fin rays, 12–15 scales rows above lateral line, 10–14 premaxillary teeth, 15–21 dentary teeth, 8–10 endopterygoid teeth, and 14 precaudal vertebrae. The third species is widespread in rio Parnaíba basin, and can be diagnosed by absence of lateral line stripe, absence of superior midlateral stripe, 182–228 anal-fin rays, 12–15 scales rows above lateral line, 107–131 lateral line scales, 32–34 premaxillary teeth, 35–44 dentary teeth, 9–12 endopterygoid teeth, and 13 precaudal vertebrae. A dichotomous key and the conservation status for the three species are provided.

A new species of the rare deep-sea genus Sciadonus Garman, 1899 (Teleostei, Bythitidae) from off Brazil, with a discussion of the evolution of troglomorphism and miniaturization in the aphyonid clade

A new species of the rare, deep-sea genus Sciadonus Garman, 1899 (Bythitidae) is described based on two specimens obtained by the Brazilian R/V Alpha Crucis on the continental slope off São Paulo State, Southeastern Brazil, western South Atlantic. It differs from its congeners by the combination of the following characters: body pale lacking dark pigmentation except for on female claspers; a pair of dermal tissue flaps anteriorly on lower jaw; pelvic-fin rays present; precaudal vertebrae 39 or 40 and total vertebrae 74 or 75. The key to the species of Sciadonus is updated. A discussion of the presence and differentiation between troglomorphic and miniature characteristics among the species in the aphyonid clade is provided and compared with other bythitids.

Bidenichthys okamotoi, a New Species of the Bythitidae (Ophidiiformes, Teleostei) from the Koko Seamount, Central North Pacific

Two specimens from the Koko Seamount (Koko Guyot), in the Hawaiian-Emperor seamount chain, Central North Pacific, caught in 2009 and 2010 are here described as a new species, Bidenichthys okamotoi. The taxonomy of the species in the genera Bidenichthys Barnard, 1934, and Fiordichthys Paulin, 1995, has been confusing due to the lost type of B. consorbrinus (Hutton, 1876) and the rarity of some of the species. Following the synonymization of Fiordichthys Paulin, 1995, with Bidenichthys by Møller and Nielsen 2015 and of Bidenichthys beeblebroxi Paulin, 1995, with Bidenichthys consobrinus Hutton, 1876, the genus Bidenichthys now comprises five species: B. capensis, B. consobrinus, B. okamotoi, B. paxtoni and B. slartibartfasti. Bidenichthys okamotoi differs from its congeners in, e.g., the fewer precaudal vertebrae (12 vs. 13), more palatine teeth rows (4–6 vs. 2–3), shorter pelvic fins (12.1–13.4% vs. 14.4–21.0% SL), max size (187 vs. 147 mm SL) and the shape of the sulcus of the otolith. We here present an updated diagnosis of the genus. A computed tomography (CT) scan of the holotype of B. okamotoi provides for additional anatomical details. The disjunctive occurrence of Bidenichthys okamotoi on the Emperor Seamount chain about 7500 km from the nearest congeneric taxon in New Zealand is discussed. The fossil otolith-based record of the genus Bidenichthys and its systematic implications is briefly discussed.

A new candiru of the genus Paracanthopoma (Siluriformes: Trichomycteridae) from the Araguaia River basin, central Brazil.

A new species of the candiru genus Paracanthopoma is described from the floodplains of the Bananal Island, a transition area between the Cerrado and Amazon, in the Araguaia River basin, central Brazil. Paracanthopoma cangussu sp. nov. is distinguished from its congeners, Paracanthopoma parva and Paracanthopoma saci, by the presence of seven opercular odontodes, five dentary teeth, five median premaxillary teeth, and first dorsal-fin pterygiophore in a vertical through the centrum of the 23th or 24th vertebra. It is further distinguished from each congener by an exclusive combination of character states, comprising the number of vertebrae, number of precaudal vertebrae, number of dorsal procurrent caudal-fin rays, number of ventral procurrent caudal-fin rays, number of dorsal-fin rays, disposition of pores on the cephalic portion of the latero-sensory system, absence of an anterior process on the anterior margin of parieto-supraoccipital, number of dorsal-fin pteryigiophores and number of interopercular odontodes. Although vandelliines are known for being exclusively hematophagous, with guts gorged with blood, two cleared and stained specimens of P. cangussu sp. nov. had Chironomidae larvae (Insecta) on their guts. Because most specimens of P. cangussu sp. nov. were collected with stomachs filled with blood, it was hypothesized that the species feeds accidentally or occasionally on insects.

Skeletal structure as taxonomic tool for identification of mullet species (Teleostei: Mugilidae) from Aceh waters, Indonesia

Many members of the mullets (family Mugilidae) are very similar morphologically, hence the possibility of taxonomic misidentification. This study involved the use of skeleton structure to distinguish four species of mullets, including Cremugil crenilabis, Liza macrolepis, Moolgarda engelii, and Mugil cephalus, harvested from Aceh waters, Indonesia. The mullets samples were collected from 10 locations, and a total of 10 samples were taken randomly as representatives of each species. The skeletal sample was prepared using the dry method. The results showed the presence of 8 pairs of ribs in C. crenilabis and L. macrolepis, while M. engelii had 9, with 10 in M. cephalus. In addition, the origin of the haemal canal of C. crenilabis is at the 12th vertebrae, extends to the 23rd, while for the other three species it starts at the 10th and extends to the 23rd. In addition, C. crenilabis possesses 12 haemal canals, but the rest have 14. The haemal canal is present in the last precaudal vertebrae of all specimens, except C. crenilabis, whose epural bone in the caudal skeleton is small and located far from the preural, while a larger and distinctly attached form is observed in the rest. Furthermore, L. macrolepis possess a pair of diapophyses, which laterally extend in the 2nd vertebrae. This bone is absent in the three other species. The presence of diapophyses, the number of ribs and haemal canals and the location of the epural bone in the caudal skeleton, and the condition of frontal attachment to the sphenotic are the important characters in distinguishing the four investigated species of mullets.

A progressive extirpation: an overview of the fossil record of Salamandrina (Salamandridae, Urodela)

ABSTRACT Salamandrina is the only extant representative of the Salamandrininae, characterised by a unique suite of morphological, ecological, and ethological features. The Salamandrina species are endemic of Italy, although their past distribution included different areas of Europe. Fossil remains belonging to this genus were previously described from the Miocene of Hungary, Mio-Pliocene transition of Greece, and Pliocene of Sardinia. The fossil record of this genus is herein expanded, with detailed descriptions of pre-caudal and caudal vertebrae from the Miocene of Germany (Petersbuch), Greece (Ano Metochi), Sardinia (Oschiri), and Spain (La Gloria, La Roma, Masada Ruea, Puente Minero), and the Pleistocene of Italy (Montagnola Senese). Otic-occipitum complexes and limb elements referred to Salamandrina are also described from the Miocene of La Roma (Spain). All these remains are referred to Salamandrina sp., given that identification at the species level of the retrieved skeletal elements is not possible. Nevertheless, the fossil record clearly indicates that the current range of this genus is the result of a prolonged extirpation process that ultimately led to the significant shrinkage of the original range or, at least apparently, to a late dispersal into the Italian Peninsula.

Discovery of a colossal slickhead (Alepocephaliformes: Alepocephalidae): an active-swimming top predator in the deep waters of Suruga Bay, Japan

A novel species of the family Alepocephalidae (slickheads), Narcetes shonanmaruae, is described based on four specimens collected at depths greater than 2171 m in Suruga Bay, Japan. Compared to other alepocephalids, this species is colossal (reaching ca. 140 cm in total length and 25 kg in body weight) and possesses a unique combination of morphological characters comprising anal fin entirely behind the dorsal fin, multiserial teeth on jaws, more scale rows than congeners, precaudal vertebrae less than 30, seven branchiostegal rays, two epurals, and head smaller than those of relatives. Mitogenomic analyses also support the novelty of this large deep-sea slickhead. Although most slickheads are benthopelagic or mesopelagic feeders of gelatinous zooplankton, behavioural observations and dietary analyses indicate that the new species is piscivorous. In addition, a stable nitrogen isotope analysis of specific amino acids showed that N. shonanmaruae occupies one of the highest trophic positions reported from marine environments to date. Video footage recorded using a baited camera deployed at a depth of 2572 m in Suruga Bay revealed the active swimming behaviour of this slickhead. The scavenging ability and broad gape of N. shonanmaruae might be correlated with its colossal body size and relatively high trophic position.

A new species of Microcharacidium (Characiformes: Crenuchidae) from the Central Amazon, Brazil

A new species (Microcharacidium bombioides sp. nov.) of the genus Microcharacidium Buckup, 1993 is described from the Rio Negro, Rio Trombetas, Rio Tapajós, tributaries of the Rio Madeira, and the middle Rio Amazonas. The new species is promptly distinguished from all congeners (Microcharacidium eleotrioides (Géry, 1960), Microcharacidium gnomus Buckup, 1993, and Microcharacidium weitzmani Buckup, 1993) by the presence of 12 circumpeduncular scales, 19 precaudal vertebrae, and 7 dark bars on the flanks connected to their contralateral parts both dorsally and ventrally; 2 short, dark suborbital stripes; all teeth on both jaws conical; 10–11 total dorsal-fin rays; and 3–4 perforated lateral line scales. An updated identification key for the genus is provided and the affinities of the new species with other Microcharacidium are discussed.

A new species of the cave-fish genus Lucifuga (Ophidiiformes, Bythitidae), from eastern Cuba.

Recently, a barcoding study and a molecular phylogenetic analysis of the Cuban species of the cave-fish genus Lucifuga Poey, 1858 revealed the existence of different evolutionary lineages that were previously unknown or passed unnoticed by morphological scrutiny (i.e., cryptic candidate species). In the present study, Lucifuga gibarensis is described as a new species restricted to anchialine caves in the northeastern karst region of the main island. The species was earlier described as a variety of Lucifuga dentata, but since the name was introduced as a variety after 1960, it is deemed to be infrasubspecific and unavailable according to the International Code of Zoological Nomenclature Art. 15.2. The new species differs from L. dentata by pigmented eyes vs. eyes absent and lack of palatine teeth vs. present. Lucifuga gibarensis seems to be most similar to the Bahamian species L. lucayana by showing pigmented eyes, 13 or 14 precaudal vertebrae and ten caudal fin rays. However, differs from it by a larger size of the pigmented eye (1.1–1.9 vs. 0.9–1.0% SL) and number of posterior lateral line neuromasts (30–33 vs. 34–35).

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

A new species of deep-water dogfish shark, Squalus shiraiisp. 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 shiraiisp. 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 shiraiisp. 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 North-western Pacific Ocean is given and main morphological differences between S. shiraiisp. nov. and the closest related species are discussed.