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| Acroteriobatus leucospilus (Norman, 1926) in Weigmann, Ebert & Séret, 2021. |
Abstract
Recent sampling efforts and examinations of museum material provided evidence for a complex of species within Acroteriobatus leucospilus (Norman, 1926). The present manuscript contains a redescription of A. leucospilus involving the syntypes and additional material, as well as formal descriptions of two new species of Acroteriobatus Giltay, 1928. All specimens of both new species were found in the western Indian Ocean. Individuals of the first new species, hereafter referred to as Acroteriobatus andysabini sp. nov., were identified originating from Madagascar, and specimens of the second new species, hereafter referred to as Acroteriobatus stehmanni sp. nov., were only found off Socotra Islands at the junction between the Gulf of Aden and the Arabian Sea. Both new species appear to be endemic to the respective region and allopatric to A. leucospilus and occur in coastal waters to at least 80 m and 43 m depth, respectively. They differ from A. leucospilus in a number of characteristics including the maximum size and coloration in fresh. Acroteriobatus andysabini sp. nov. is a large species growing to more than 100 cm total length (TL) and with elongated bluish-gray spots on snout giving “stripe-nosed” appearance; numerous small bluish-gray spots on pectoral, pelvic, dorsal, and caudal fins; brown spots on trunk and fin bases; lateral tail folds striped orange and white; and ventral surface largely white but with a V-shape pattern of faint to dark speckled black spots on snout tip. Acroteriobatus stehmanni sp. nov. is a small species growing to ~62 cm TL and with sparse patterning with small bluish-gray circular spots confined to snout tip, posterior pectoral-fin margins, a pair on midbody, and few on posterior pelvic-fin margins, rather indistinct small to larger dark brown spots, and lateral tail folds and ventral surface white. Acroteriobatus leucospilus is a medium-sized species growing to ~96 cm TL and with patterning similar to A. andysabini sp. nov. but ventral surface uniformly white and lateral tail folds white or striped blue and brown. Taxonomical differences include nasal lamellae counts (42–48 in A. andysabini sp. nov. vs. 43–48 in A. stehmanni sp. nov. vs. 37–41 in A. leucospilus), snout angle (76–85° vs. 71–77° vs. 68–81°), and dorsal head length (24.2–33.5% vs. 17.2–22.8% TL vs. 24.0–29.2% TL). A key to the species of Acroteriobatus is given for the first time.
Keywords: Chondrichthyes, Elasmobranchii, Systematics, Guitarfishes, Taxonomy, Morphology
Family Rhinobatidae Bonaparte 1835
Genus Acroteriobatus Giltay, 1928
Type species: Rhinobatus (Syrrhina) annulatus Smith
in Müller & Henle, 1841
by subsequent designation
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| Acroteriobatus andysabini sp. nov., Fig. 1 SAIAB 97396, juvenile male holotype, 565 mm TL fresh, in total dorsal view taken directly after catching. Photograph by Elaine Heemstra, NRF-SAIAB Fig. 2 SAIAB 97396, juvenile male holotype, 550 mm TL, in total dorsal view. Scale bar: 5 cm. Photograph courtesy Marsha Englebrecht. Fig. 3 SAIAB 97396, juvenile male holotype, 550 mm TL, in total ventral view. Scale bar: 5 cm. Photograph courtesy Marsha Englebrecht. |
Acroteriobatus andysabini sp. nov. Weigmann, Ebert & Séret
Diagnosis: A large Acroteriobatus species distinguished by the following combination of characters: dorsal surface smooth, without prominent thorns or tubercles, except for enlarged granular denticles partially around orbital rims and irregularly distributed along midline from nape to somewhat anterior to first dorsal-fin origin; absent between dorsal fins and upper caudal fin. Snout semi-translucent with elongated bluish-gray spots giving “stripe-nosed” appearance, numerous small bluish-gray spots covering disc and pectoral, pelvic, dorsal, and caudal fins on a brown background with larger, slightly darker, indistinct brown spots covering the tail and fin bases; outer edges of pelvic-fin margins white, lateral tail folds striped orange and white; ventral surface white, except for a V-shape pattern of faint to dark speckled black spots on snout tip. Nasal lamellae 42–48; upper jaw tooth row count ~80–87; 179–185 post-synarcual centra; 195–200 total vertebral segments; 64–68 total pectoral skeleton radials.
Distribution: Acroteriobatus andysabini sp. nov. is presently only known from the coastal waters surrounding Madagascar and may be endemic to this region (Fig. 13). Records are from off Tôlanaro, Anosy region, and Cape Andavaka (southeastern Madagascar), Toliara and Ankilibe (southwestern Madagascar), and Antongil Bay (northeastern Madagascar). Its depth range is from shallow coastal waters to at least 80 m. Fricke et al. (2018) reported A. leucospilus as a new species record for Madagascar but commented that the species had been misidentified previously as Rhinobatos (= Acroteriobatus) annuulatus by several earlier authors.
Etymology: The species name andysabini is in honor of Andy Sabin for his gracious support of the Lost Sharks project at the Pacific Shark Research Center.
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| Acroteriobatus stehmanni sp. nov. Fig. 16 ZMH 25557, adult female paratype, 602 mm TL fresh, in total dorsal view taken directly after catching. Scale bar: 5 cm. The photograph was taken and kindly provided by Matthias Stehmann. Fig. 17 ZMH 25558, adult female paratype, 594 mm TL fresh, in total dorsal view taken directly after catching. Scale bar: 5 cm. The photograph was taken and kindly provided by Matthias Stehmann. Fig. 14 ZMH 25553, adult male holotype, 597 mm TL, in total dorsal view. Scale bar: 5 cm. Fig. 15 ZMH 25553, adult male holotype, 597 mm TL, in total ventral view. Scale bar: 5 cm |
Acroteriobatus stehmanni sp. nov. Weigmann, Ebert & Séret
Diagnosis: A small Acroteriobatus species distinguished by the following combination of characters: dorsal surface smooth, without prominent thorns or tubercles, except for slightly enlarged granular denticles partially around orbital rims and rather regularly distributed along midline from nape to or to somewhat anterior to first dorsal-fin origin; absent between dorsal fins and upper caudal fin. Snout semi-translucent with a few, somewhat elongated bluish-gray spots only giving it a very reduced stripe-nosed appearance, patterning with small bluish-gray circular spots generally sparse and confined to symmetrical patterns on snout tip, posterior pectoral-fin margins, a pair of tiny spots on midbody behind occipital joint, and few spots on posterior pelvic-fin margins; indistinct brown spots on the body and dorsal and caudal fins; ventral surface white except for a blackish blotch and two tiny black spots on ventral snout tip in smallest juvenile paratype. Nasal lamellae 43–48; upper jaw tooth row count ~64–78; 181–186 post-synarcual centra; 194–200 total vertebral segments; 63–67 total pectoral skeleton radials.
Distribution: Acroteriobatus stehmanni sp. nov. is presently only known from the coastal waters surrounding the Socotra Islands and may be endemic to this region (Fig. 13). It is known from 36 to 43 m depth.
Etymology: The species is named in honor of Dr. Matthias F.W. Stehmann for his invaluable contributions to chondrichthyan taxonomy, particularly with respect to skates. He taught SW and BS chondrichthyan taxonomy, collected all type specimens of the new species, and kindly provided fresh photographs of two of them.
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| Acroteriobatus leucospilus, underwater photograph showing the vivid live coloration. photograph by Dennis King. |
Acroteriobatus leucospilus (Norman, 1926)
(Blue-spotted guitarfish)
Diagnosis: A medium-sized Acroteriobatus species distinguished by the following combination of characters: dorsal surface smooth, without prominent thorns or tubercles, except for slightly enlarged granular denticles partially around orbital rims and rather regularly distributed along midline from nape to near first dorsal-fin origin; absent between dorsal fins and upper caudal fin. Snout semi-translucent with elongated bluish spots giving stripe-nosed appearance, numerous small bluish spots covering snout, pectoral, pelvic, dorsal, and caudal fins but not central disc on a sandy brown background with darker brown spots of varying sizes covering the disc, tail, fin bases, and fins, sometimes giving the caudal peduncle a striped appearance; outer edges of pectoral- and pelvic-fin margins blue, lateral tail folds white or striped blue and brown; ventral surface white. Nasal lamellae 37–41; upper jaw tooth row count ~60–75; 187–192 post-synarcual centra; 200–205 total vertebral segments; 63–70 total pectoral skeleton radials.
Distribution: Acroteriobatus leucospilus so far has been recorded from off the central Transkei coast (Eastern Cape Province) to the northern KwaZulu-Natal Province (South Africa) and Mozambique. Ebert et al. (2021), based on the examined material, extended its range to Zanzibar and Dar es Salaam, Tanzania (Fig. 13). It is known from 0 to 100 m depth (Compagno et al. 1989; Séret et al. 2016; Weigmann 2016) but seems to be most abundant in depths of around 20 fathoms or 37 m (Wallace 1967).
Simon Weigmann, David A. Ebert and Bernard Séret. 2021. Resolution of the Acroteriobatus leucospilus Species Complex, with A Redescription of A. leucospilus (Norman, 1926) and Descriptions of Two New western Indian Ocean Species of Acroteriobatus (Rhinopristiformes, Rhinobatidae). Marine Biodiversity. 51, 58. DOI: 10.1007/s12526-021-01208-6
