Acroteriobatus omanensis Last, Henderson & Naylor, 2016, sp. nov.
Creators: name: Last, Peter R.
name: Henderson, Aaron C.
name: Naylor, Gavin J. P.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Elasmobranchii
Rajiformes
Rhinobatidae
Acroteriobatus
Acroteriobatus omanensis

description: Acroteriobatus omanensis sp. nov.
[English Name: Oman Guitarfish] (Figs 1–7, Tab. 1)
Acroteriobatus sp.: Henderson et al., 2016 (tissues GN 8528, 8529, 8530).
Holotype. CSIRO H 7551-01, female 586 mm TL, off Muscat, Gulf of Oman (collected Muttrah fish market, Muscat), Oman, A. Henderson, shallower than 100 m depth, late March/early April 2003.
Paratypes. 3 specimens. CSIRO H 7552-01 (desiccated slightly), adult male 497 mm TL, off Muscat, Gulf of Oman (collected Muttrah fish market, Muscat), Oman, A. Henderson, probably caught in less than 100 m, November 2002 or August 2003; Sultan Qaboos University (uncatalogued), female 590 mm TL, female 601 mm TL, off Muscat, Gulf of Oman (collected Muttrah fish market, Muscat), Oman, A. Henderson, 21 August 2011.
Other material. Sultan Qaboos University (lost on freezer failure, photographic images, two females (sizes not specified), collected with paratypes above, A. Henderson, 21 August 2011.
Diagnosis. A species of the genus Acroteriobatus distinguished by the following combination of characters in adults: wedge-shaped disc, width 29–33% TL, disc length 1.3–1.4 times width; short snout, angle 59–67o, length 2.6–3.0 times interspiracular distance, 4.0–4.4 times interorbital width; medium-sized orbit, 1.3–1.6 times spiracle length; nostrils oblique, their length 1.2–1.3 times internarial distance; preoral length 6.3–6.8 times internarial distance; anterior nasal flaps extending across internarial space and barely separated at mid-snout; posterior nasal flaps very broad; two well-developed spiracular folds, outermost fold distinctly taller than inner fold; ridges of rostral cartilage almost parallel, converging slightly anteriorly but not constricted medially; anterior cartilage sickle shaped, pointed posteriorly; distance between fifth gill slits 2.7–3.0 times in ventral head length; prebranchial sensory pore patch obvious, extending to first gill slit; postscapular sensory canal prominent, with exposed lateral pores, grooved; thorns patches on supraorbit, scapular region, and dorsal midline rudimentary, inconspicuous; pelvic-fin inner margin slightly longer than its base in males, lengths subequal in females; interdorsal distance 2.7– 3.2 times first dorsal-fin base; dorsal caudal margin 2.0–2.7 times preventral margin; upper jaw with ~86 tooth rows; ~185–188 post-synarcual centra; 37–42 nasal lamellae; dorsal disc greenish brown with dense pattern of small white ocelli and fainter darker brown blotches; margins of nasal flaps vivid red or orange; dorsal fins with small white spots; and caudal fin with two large dark blotches on each side (near fin base and on ventral lobe), and a prominent pair of dark saddles on caudal peduncle.
Description. Disc bottle-shaped, bluntly angular anteriorly, snout angle before eyes acute (in female holotype 67o, more acute in adult male paratype, 59o); anterior margin undulate, outer margins broadly rounded, posterior margins convex, rear tip narrowly rounded distally; its length 1.34 in holotype (1.43 in adult male paratype, 1.31– 1.32 in female paratypes) times its width. Pelvic fins elongate, short-based, base length 1.25 (damaged in adult male paratype, 1.10–1.25 in female paratypes) times inner margin length; pelvic-fin total length 1.77 (damaged, 1.72–1.93) times base length, 2.51 (damaged, 2.32–2.56) times width; anterior margin weakly concave anteriorly then becoming weakly convex, apex broadly rounded, posterior margin weakly convex, free tip very narrowly rounded. Tail elongate, more slender anteriorly in adult male paratype, tapering weakly; very strongly depressed, in cross-section nearly flat below, more rounded above; tail length from anterior cloaca 1.42 (1.46, 1.33–1.37) times precloacal length, 1.41 (1.43, 1.32–1.35) times disc length, 5.58 (6.43, 4.94–5.10) times its width at pelvic-fin insertions; tail width 2.43 (2.44–2.68 in all paratypes) times depth at pelvic-fin insertions, 2.71 (2.53–2.90) at first dorsal-fin origin, 2.20 (2.17–2.36) at second dorsal-fin origin. Dermal fold lateral on tail, originating slightly behind free rear tip of pelvic fin, reaching onto base of caudal fin just behind ventral origin of caudal fin; fold narrow, maximum width at interdorsal space much less than half width of posterior nasal flap, slightly narrower than length of shortest spiracular fold. Head moderately elongate, ventral length 26.0 (28.3, 26.8–26.9)% TL; snout rather short, preoral length 3.08 (3.23, 2.94–3.05) times mouth width, 6.64 (6.33–6.76) times internarial distance, 1.24 (1.30, 1.22–1.25) times dorsal caudal-fin margin, 4.42 (5.48, 4.54–4.59) times distance from nostril to margin of disc; preorbital snout length (direct) 2.68 (2.97, 2.64–2.73) times interspiracular distance, 3.16 (3.10–3.66) times orbit, 4.01 (4.11–4.35) times interorbital width; interorbital space weakly concave, rather narrow; eyes rather large, dorsolateral, not elevated or protruding, orbit diameter 1.51 (1.33–1.58) times spiracle length, 1.27 (1.12–1.40) times interorbital distance. Spiracles narrowly bean-shaped, relatively large; two prominent and strongly compressed folds on posterior margin, length of innermost spiracular fold about 2/3 of outer fold; distance between bases of folds slightly less than length of shortest fold. Nostril moderately large, oblique, all nasal flaps well developed; anterior aperture subcircular; nostril length 3.28 (3.55, 3.11–3.22) times anterior aperture width, 0.96 (1.03–1.05) times anterior nasal-flap base length, 0.87 (1.04, 0.88–0.89) times distance from nostril to edge of disc, 1.31 (1.21–1.32) times internarial distance. Anterior nasal-flap base greatly extended, penetrating horizontally into internarial space, mesial edges barely separated (by about length of inner spiracular fold); innermost extension of flap not narrow; flap base length 2.10 (1.68–2.15) times its width at process, 3.43 (3.01–3.41) times anterior aperture width; minimum distance between mesial insertions of flaps 18.6 (11.8–13.7) in greatest distance across nostrils anteriorly, 5.72 (3.51–4.53) in internarial distance; process of flap about twice as long as wide, bluntly pointed distally, abutting posterolateral nasal flap and determining hind margin of anterior aperture, and overlapping posterior nasal flap. Posterolateral nasal flap lobe-like, broadest medially, length 3.57 (3.53–3.81) times width; originating just behind lateral extremity of anterior nasal aperture, extending postero-mesially as a free fold almost to level of insertion of posterior nasal flap. Posterior nasal flap well-developed, lobe-like, base length 1.76 (1.72–1.97) times its width, its inner edge close to innermost margin of nostril; width 1.09 (1.28, 1.00– 1.08) times anterior aperture width, 1.30 (1.60, 1.42–1.45) times posterolateral nasal-flap width. Mouth width 1.65 (1.63–1.74) times nostril length, 7.78 (7.22, 7.63–7.66) in precloacal length; positioned beneath hind margin of orbit. Upper jaw almost straight, upper lip not arched; lower lip not pronounced, not separated from well-developed oral groove by ridges of strongly corrugated skin; short lateral grooves at corners of mouth. Teeth very small, blunt; crowns rhomboidal, acuspid; teeth quincuncial, in ~ 86 rows in upper jaw of holotype; upper and lower jaw teeth similar in shape and size, larger at symphysis than near corner of mouth. Gill openings s-shaped; length of third gill slit 1.58 (2.05, 1.49–1.82) in nostril length, 4.72 (4.52–5.56) in distance between fifth gill slits; distance between first gill slits 1.42 (1.38–1.43) times distance between fifth gill slits, distance between fifth gill slits 3.90 (3.35, 3.70–3.99) times internarial distance, 1.81 (1.66–1.78) times mouth width, 0.37 (0.33, 0.36–0.37) of ventral head length. Dorsal fins relatively tall and short-based; apices narrowly rounded; anterior margins weakly convex; posterior margins weakly concave; free rear tips almost forming right angle, not produced, second dorsal more angular than first; fins similar in height, first dorsal slightly more upright than second; length of first dorsal 0.73 (0.93, 0.75–0.81) times its height, base length 1.94 (1.57, 1.88–2.02) times inner margin length; second dorsal-fin length 0.92 (1.05, 0.88–0.95) times its height, base length 2.72 (1.97, 2.29–2.43) times inner margin length. First dorsal fin well behind pelvic-fin rear tips, interspace 1.10 (0.94–1.10) times interdorsal distance; interdorsal space relatively short, 1.66 (1.94, 1.54–1.69) times second dorsal-fin height, 2.86 (3.18, 2.69–2.92) times base of first dorsal fin, 1.16 (1.38, 1.12–1.16) times tail width at origin of first dorsal fin, 1.51 (1.61–1.87) times interspace between second dorsal-fin insertion and upper origin of caudal fin. Caudal fin relatively small; dorsal caudal margin weakly convex, length 2.00 (2.66, 2.19–2.23) times preventral margin length; ventral lobe broadly rounded; posterior margin weakly concave; fin apex pointed.
Dermal denticles minute, close-set, covering entire body and fins (except posterior edges of dorsal fins); skin surfaces velvety; dorsal denticles enlarged slightly along midbelt of body and on superorbit; some enlarged slightly on midline of tail between dorsal fins, precaudal midline, snout tip, and lateral margin of disc anteriorly; present over nasal lamellae. Spines blunt, globular to seed-shaped, minute and rudimentary; cusps low, blunt distally, anterior edges often crenulated; orbital spine patch weak, with small row along margin of preorbit and one spine near posterior margin of spiracle (barely evident without magnification); a few similar globular spines on dorsal midline, variable in shape and size; 2 very small globular spines on each shoulder. Prebranchial sensory pore patch distinct, extending to near lateral edge of first gill slit. Postscapular sensory canal prominent, weakly undulated anteriorly, terminating about an eye diameter forward of pectoral-fin insertions; sensory pores evident; sensory canals not forming shallow grooves.
Holotype Paratype (male) Paratypes (female)
Min Max ......continued on the next page Holotype Paratype (male) Paratypes (female)
Min Max Rostral cartilage firm, broad, its shaft barely increasing in width in a posterior direction; rostral node broadly expanded laterally and elongate, narrowly rounded apically (not angular), axis at widest part of node ~17% of length of rostral cartilage from snout tip; precerebral cavity relatively broad posteriorly, converging to a point anteriorly at rostral node, dorsolateral edges of cartilage surrounding cavity (rostral ridges on surface of snout) well separated posteriorly, not constricted medially; rostral cartilage about 59% of length of neurocranium, ventral edges of rostral cartilage almost united; nasal capsules large, their transverse axes anterolaterally directed; maximum width across capsules (cranium width) 1.5 times nasobasal length of cranium (base of rostrum to occipital condyles); length of nasal capsule slightly shorter than its width; basal plate narrow, its minimum width 3.9 in nasobasal length; cranial roof with small elongate oval fenestra, located behind precerebral cavity by a distance well exceeding its length; anterior cartilage narrowly triangular, sickle shaped, posterior apex narrowly rounded, without a small anterior lobe; preorbital and postorbital processes weak. Nasal lamellae 37–42. Pectoral skeleton with 32–33 (31, n=1) propterygial, 9 (8–9) mesopterygial, 2 (0–1) neopterygial, 27–28 (27) metapterygial, 71 (67) total radials; anterior radials of propterygium extending forward of nasal capsules by ~27% of posterior rostral length. Total pelvic radials unclear, ~ 28–29 in female holotype, ~ 24 in male paratype, excluding clasper; clasper of paratype weakly calcified. Vertebral column with ~198 (~202) total segments (synarcual and free), ~185 (~188) post-synarcual centra; 156 (157) total precaudal centra; 13 (14) synarcual segments; 27 (27) monospondylous precaudal centra; 116 (116) diplospondylous precaudal centra, 42 (45) diplospondylous caudal centra.
Colour. Fresh, female paratype MUT 210811 -2 (see Fig. 2 A, B): Dorsal surface medium greenish brown, paler along pectoral-fin and pelvic-fin posterior margins and on snout beside rostral cartilage; skin covered with faint darker brown blotches and numerous small ocelli; orbital membrane brown, darker than head; pair of narrow, dark saddles on caudal peduncle (below inner margin of second dorsal fin and at caudal-fin base). Ocelli consisting of a white central spot surrounded by a dark, diffuse-edged brownish rim; symmetrically arranged, largest on central part of body, becoming smaller laterally; more-or-less evenly spaced; brownish blotches slightly larger than ocelli. Dorsal fins lightly covered with small white spots; caudal fin similarly white-spotted with two large dark blotches on each side (near fin base and on ventral lobe). Ventral surface whitish, with diffuse irregular dark marking on white at snout tip (male paratype lacking dark marking); mid-snout, oronasal region, intergill and posterior pectoral margin yellowish; margins of nasal flaps reddish (orange in some paratypes) and strongly contrasted with nostrils. In preservative, holotype CSIRO H 7551-01 (Fig. 1 A, B): body more brown than in fresh paratype; brownish blotches and white ocelli less obvious; outer rims of ocelli appearing bluish grey; nasal flaps with narrow reddish or orange margins in all types.
Size. Three adult females (including the holotype) were 586–601 mm TL. Only available male, mature at 497 mm TL, suggests this is a small guitarfish. Number of embryos and birth size unknown.
Distribution. Known only from landings at Muttrah fish market (Muscat), indicating a local presence in the Gulf of Oman, Arabian Sea. Despite regular market and field surveys along the entire coast of Oman spanning almost 10 years, the species has not been recorded elsewhere. Similarly, the species has not been recorded from market surveys within the Persian Gulf (e.g. Moore et al., 2012).
Etymology. Epithet based on the general collection locality of the types, the Gulf of Oman.
B Comparisons. The body shape of Acroteriobatus omanensis sp. nov. is most similar to A. annulatus, A. ocellatus, A. variegatus and A. zanzibarensis (disc distinctly wedge-shaped and snout narrowly pointed), rather than A. blochii, A. leucospilus and A. salalah (disc shovel-shaped or heart-shaped with a more broadly rounded to obtuse snout). Acroteriobatus omanensis sp. nov., A. annulatus and A. ocellatus have more-or-less ocellated dorsal colorations but only A. omanensis is brownish with numerous small symmetrically arranged ocelli consisting of a white centre surrounded by a darker brown rim. Acroteriobatus annulatus is lighter brown with a more-or-less symmetrical pattern of dark spots or small ocelli, each consisting of a small central dark spot surrounded by a darkedged pale ring. Acroteriobatus ocellatus is also brownish with numerous irregularly shaped ocelli with bluishgrey centres surrounded by a dark brown rim. Acroteriobatus omanensis sp. nov. also has a narrower disc (length 1.3–1.4 vs. ~1.1 times its width in A. annulatus and A. ocellatus) and the snout apex is much more narrowly pointed than in any of its congeners. Descriptions of the members of the genus are based on early first accounts or are largely incomplete and a generic revision is needed.
description: Published as part of Last, Peter R., Henderson, Aaron C. & Naylor, Gavin J. P., 2016, Acroteriobatus omanensis (Batoidea: Rhinobatidae), a new guitarfish from the Gulf of Oman, pp. 276-286 in Zootaxa 4144 (2) on pages 277-282, DOI: 10.11646/zootaxa.4144.2.9, http://zenodo.org/record/264397