Rhinobatos annandalei Norman 1926

Last, Peter R., Séret, Bernard & Naylor, Gavin J. P., 2019, Description of Rhinobatos ranongensis sp. nov. (Rhinopristiformes: Rhinobatidae) from the Andaman Sea and Bay of Bengal with a review of its northern Indian Ocean congeners, Zootaxa 4576 (2), pp. 257-287 : 259-265

Rhinobatos annandalei Norman 1926

Bengal Guitarfish

( Figs 1–3 , 10–12 ; Table 1)

Rhinobatus columnae (nec Bonaparte): Day, 1888, Fishes of India Suppl: 811; Day, 1889, Fauna of India, Fishes 1, 44.

Rhinobatus annandalei Norman, 1926 , Proc. Zool. Soc. London 1926 (62), 960, fig. 13.

Rhinobatos annandalei: Misra, 1969 , Fauna of India, Pisces (2 nd Edition) 1, 102.

Rhinobatos cf. annandalei: Psomadakis et al., 2015 , Field identification guide to the living marine resources of Pakistan, 99, fig.

Rhinobatos punctifer (nec Compagno & Randall, 1987): Randall & Compagno, 1995, Raffles Bulletin of Zoology, 292–3, fig 3; Randall, 1995, Fishes of Oman, 43, fig 58; Henderson et al., 2016, Arabian Elasmobranch Taxonomy, 431, fig. 8; Akhilesh et al., 2014, Checklist Chondrichthyans India:115–118 (listed); Vincent et al., 2018, Landings in India: 6–8 (listed).

Material examined. Lectotype (newly designated). BMNH 1909.7 .12.1 [ex ZSI], immature male 423 (originally as 415) mm TL, Bay of Bengal , east channel, mouth of Hooghly River, India, ~ 70 m depth . Paralectotype (newly designated). BMNH 1909.7 .12.2, female 398 mm TL, collected with lectotype .

Other material. 9 specimens. CSIRO 7621-02 (specimen 7), immature male 446 mm TL, Karachi fish market, Pakistan, collected B. Osmany, 24 Apr 2014 ; CSIRO unreg, (specimen 58), female 558 mm TL, CSIRO 7622-01 (specimen 59), female 780 mm TL, CSIRO 7622-02 (specimen 60), adult male 666 mm TL, CSIRO 7622-03 (specimen 57), adult male 665 mm TL, Karachi fish market, Pakistan, collected B. Osmany, 26 May 2014 ; CSIRO 7866-01 (specimen 244), female ~ 870 mm TL, Bay of Bengal , N of Andaman Is, Myanmar, 14°40.56’ N, 93°44.93’ E, bottom trawl, 88 m depth, RV Dr Fridtjof Nansen station 59, collected P. Psomadakis, 9 May 2015 ; CSIRO unreg, (specimen 25), female 621 mm TL, Karachi fish market?, Pakistan, 12 Oct 2013 ; PMBC 6736 , female 493 mm TL, northern Andaman Sea , Myanmar, 90–140 m depth, 3 Nov 1989 ; SQU unregistered, adult male 681 mm TL, Gulf of Oman, As Seeb fish market, Muscat, Oman, collected P. Last, 11 July 2012 .

Diagnosis. Diagnosis. A medium-size species of the genus Rhinobatos (attaining at least 870 mm TL) distinguished by the following combination of characters: disc large, broadly wedge-shaped, width 38–44% TL, length 1.1–1.2 times width; snout relatively short, length 2.5–2.8 times interspiracular distance, 3.5–3.9 times interorbital width; orbit diameter 1.1–1.8 times spiracle length; nostrils weakly oblique, their length 1.3–1.5 times internarial distance; mouth width 7.1–8.0% TL; preoral length 5.6–5.7 times internarial distance; posterior nasal flaps broad; two spiracular folds, outermost fold slightly taller than inner fold; ridges of rostral cartilage; anterior cartilage sickle shaped, bilobed posteriorly; distance between fifth gill slits 2.4–2.8 times in ventral head length; prebranchial sensory pore system obvious, extending posteriorly to margin of first gill slit; postscapular sensory canal obvious, notched, with exposed lateral pores; conspicuous thorn patches on supraorbit and scapular region, and row of short pungent thorns along dorsal midline; dorsal fins almost entirely covered with minute denticles; dorsal fins moderately tall, height of first 7.0–8.6% TL; pelvic-fin inner margin subequal to or shorter than its base length; interdorsal distance 2.2–2.4 times first dorsal-fin base; dorsal caudal margin 2.0–2.7 times preventral margin; upper jaw with 126–130 tooth rows; snout angle ~70°; 67–70 pectoral radials; 158–165 post-synarcual centra; 54–59 nasal lamellae; dorsal fins almost entirely brownish or greyish; dorsal disc brownish or greyish, with a symmetrical pattern of small, widely spaced white spots (rectangular arrangement of four spots on head lateral to orbito-spiracular region and a triangular arrangement of three spots on nape); ventral disc and tail pale, often with variable dark blotches; no large, black, teardrop marking on undersurface of snout.

Distribution. The range of R. annandalei in the northern Indian Ocean provided by Séret et al. (2016), Oman to eastern India (Bay of Bengal), is hereby extended east to include the Andaman Sea, off Myanmar. Evidence of slight variability in squamation between populations at either end of the distribution of this species is supported by molecular data ( Fig 15 ); a single specimen from Myanmar diverged slightly from a cluster of 70 specimens collected largely from Oman, but also including material from Pakistan and Tamilnadu (southeastern India). Benthic inshore on continental shelf to 90 m depth ( Séret et al., 2016).

Remarks. Norman’s (1926) description of R. annandalei was based on two preserved syntypes (BMNH 1909.7.12.1-2, formerly deposited in the ZSI) collected from near the mouth of Hooghly River ( India) in the Bay of Bengal. The syntypes, which were photographed and measured by one of us (BS), were found to be slightly longer than their original documented sizes; the largest syntype, an immature male was remeasured at 423 (rather than 415) mm TL and a female 398 (rather than 395) mm TL. The present condition of the larger male specimen (BMNH 1909.7.12.1) was considered to be superior to the female (BMNH 1909.7.12.2) and is hereby designed as the lectotype of R. annandalei , with the smaller female becoming a paralectotype. Morphometric data collected from three newly acquired specimens of R. annandalei from Myanmar and Pakistan exhibited strong congruence with Norman’s types in morphometrics and squamation.

The status of R. annandalei has been unclear as it has been historically confused with other Rhinobatos from the Indian Ocean, such as the sympatric R. punctifer , and the western Pacific guitarfish R. schlegelii (see synonymy above), and its coloration has been a major a contributor this confusion. The colour pattern of R. annandalei , being plain pale to medium brownish or greyish with a symmetrical pattern of small (uniform in size), well-defined, widely spaced white spots on the disc and tail (some of these spots are remain evident on the syntypes), is consistent. These spots form a noticeable rectangular arrangement of four on the head lateral to orbito-spiracular region and a triangular arrangement of three spots on the nape; there are also similar paired spots near the origins of the pelvic and dorsal fins. The ventral surface can be uniformly whitish or also with large dark blotches, but an apical blotch on snout is absent. The dorsal fins are uniform in coloration (i.e. brownish or greyish) but their posterior margins can be translucent to faintly dusky. In comparison, R. punctifer is highly variable in coloration (i.e. plain, spotted, ocellated, or ocellated and reticulated), but also often has a pattern of white spots or ocelli in a similar symmetrical arrangement, which has possibly contributed to its confusion with R. annandalei . Other guitarfishes in the northern Indian Ocean are plain coloured dorsally or with dusky blotches (always lacking white spots as adults), and R. schlegelii from the western Pacific usually has a distinctive teardrop shaped marking on the undersurface of bottle-shaped snout (absent in all northern Indian Ocean Rhinobatos ).

Rhinobatos annandalei differs significantly from R. punctifer in morphometrics. The disc is proportionally much larger (width, including data from the types 38–44% vs. 29–34% TL, length 45–48% vs. 38–42% TL), the mouth broader (7–8% vs. 5–6% TL), and the tail shorter (postcloacal length 63–67% vs. 68–72% TL) in R. annandalei . Calculations the disc width to TL ratio for the R. annandalei types were 41.1% and 39.9%, compared to 33.8% for Compagno and Randall’s (1987) measurements of the adolescent male holotype. In addition, the dorsal fins of adult (and possibly juvenile) R. punctifer have a distinctive pattern of squamation with denticles concentrated on the anterior submargin and anterior base of each fin; most of the posterior fin surface is naked (or very sparsely denticulate) and this part of the fin is noticeably darker and sharply demarcated from the paler, anterior denticle covered part ( Fig. 7 ). In R. annandalei there is no sharp demarcation between squamation of the anterior and posterior parts of the dorsal fins, as the fins are almost entirely covered with minute denticles ( Fig. 3A, B ).

Thorn patches on the body are well developed in R. annandalei compared its regional congeners, although there appears to be some regional variability. In material examined, specimens observed from near the type locality (i.e. eastern Indian Ocean) have distinctly larger median, scapular, and preorbital thorns than those from the western Indian Ocean. Nevertheless, these same thorn patches are weak or absent in R. punctifer and other Indian Ocean Rhinobatos .

Figures

FIGURE 1. Dorsal views of Rhinobatos annandalei: A. immature male lectotype, 423 mm TL (BMNH 1909.7.12.1), Bay of Bengal, preserved; B. female paralectotype, 398 mm TL (BMNH 1909.7.12.2), Bay of Bengal, preserved.

FIGURE 2. Fresh specimens of Rhinobatos annandalei: A. dorsal view of adult male, 681 mm TL (SQU unreg), Oman; female, 870 mm TL (CSIRO H 786-01), Myanmar, B. dorsal view, C. ventral view.

FIGURE 3. Lateral views of the unpaired fins of Rhinobatos annandalei, female, 870 mm TL (CSIRO H 786-01), Myanmar: A. first dorsal fin; B. second dorsal fin; and C. caudal fin.

FIGURE 7. Lateral views of the characteristic first dorsal fin of Rhinobatos punctifer showing the sharply demarcated denticle covered anterior part from the near naked posterior part: A. white-spotted morph—adult male 646 mm TL (CSIRO H 7413-03), Dubai; B. plain morph—immature male 655 mm TL (CSIRO H 7623-02), Pakistan; C. ocellated morph—female 690 mm TL (CSIRO H 7623-01), Pakistan.

FIGURE 10. View of dorsal head (preserved): A. Rhinobatos ranongensis sp. nov., adult male holotype 645 mm TL (CSIRO H 7861-02); B. Rhinobatos punctifer, female 570 mm TL (MNHN 2014-0156); C. Rhinobatos annandalei, female 870 mm TL (CSIRO H 7866-01); and D. Rhinobatos lionotus, female 760 mm TL (CSIRO H 7867-01).

FIGURE 11. Views of oronasal region (preserved): A. Rhinobatos ranongensis sp. nov., adult male holotype 645 mm TL (CSIRO H 7861-02); B. Rhinobatos punctifer, female 570 mm TL (MNHN 2014-0156); C. Rhinobatos annandalei, female 870 mm TL (CSIRO H 7866-01); and D. Rhinobatos lionotus, female 760 mm TL (CSIRO H 7867-01).

FIGURE 12. Dorsal view of skin at scapulocoracoids of: A. Rhinobatos ranongensis sp. nov., adult male holotype 645 mm TL (CSIRO H 7861-02); B. Rhinobatos punctifer, adult male 643 mm TL (MNHN 2014-0157); C. Rhinobatos annandalei female 870 mm TL (CSIRO H 7867-01); and D. Rhinobatos lionotus female 760 mm TL (CSIRO H 7866-01).

FIGURE 15. Maximum Likelihood (GTR+I+G) tree derived from aligned mitochondrial NADH2 sequences (1044 sites).