Rhinobatos lionotus Norman, 1926
Smoothback guitarfish
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Family:  Rhinobatidae (Guitarfishes)
Max. size:  75 cm TL (male/unsexed)
Environment:  demersal; brackish; marine; depth range 70 - 76 m, amphidromous
Distribution:  Indian Ocean: West Bengal to Myanmar, upper Bay of Bengal (India) to possibly Arabian Sea; Sri Lanka (Ref. 114953).
Diagnosis:  This species is distinguished by the following set of characters: disc is wedge-shaped, rather large, its width 35-37% TL, its length 1.2-1.3 times width; snout is relatively short, length 2.5-2.7 times interspiracular distance, ~3.4 times interorbital width; orbit diameter 1.2-1.4 times the spiracle length; nostrils are moderately oblique, length 1.3-1.5 times internarial distance; mouth width 6.3-6.9% TL; preoral length 5.5-5.9 times internarial distance; posterior nasal flaps are broad; two spiracular folds, the outermost fold subequal to marginally taller than inner fold; ridges of the rostral cartilage almost parallel, widely separated, converging slightly anteriorly but not constricted medially; anterior cartilage weakly sickle-shaped, almost truncate posteriorly; distance between the fifth gill slits 2.5-2.7 times in ventral head length; prebranchial sensory pore system distinct, extending posteriorly to margin of first gill slit; postscapular sensory canal notched, the lateral pores exposed; with weak thorn patches on supraorbit and scapular region, and row of rudimentary thorns (inconspicuous) along dorsal midline; denticles on dorsal fins densest anteriorly, more sparse posteriorly; dorsal fins are small, height of first 7.7-8.1% TL; pelvic-fin inner margin subequal to or shorter than its base length; interdorsal distance 2.3-2.9 times first dorsal-fin base; dorsal caudal margin 1.9-2.0 times the preventral margin; upper jaw with ~118 tooth rows; snout angle ~61°; pectoral radials 68-72; post-synarcual centra ~164; nasal lamellae ~49. Colouration: dorsal fins brownish anteriorly while dusky posteriorly and apically; dorsal disc of adults is uniformly brown to greenish, with or without large, regularly spaced cloudy blotches (faint orange to dusky, more or less symmetrically arranged and of irregular sizes); ventral disc and tail are pale; undersurface of snout without large, black, teardrop marking (Ref. 123963).
Biology:  Found on benthic inshore areas on continental shelf to at least 76 m depth (Ref. 123963). Also known to inhabit river mouths. Ovoviviparous (Ref. 50449). Confused with other species in the Indian Ocean, biology unknown (Ref. 114953).
IUCN Red List Status: Data deficient (DD); Date assessed: 01 December 2008 Ref. (123251)
Threat to humans:  harmless
Country info:   

Entered by: Torres, Armi G. - 24.05.95
Modified by: Capuli, Estelita Emily - 06.04.21
Checked by: Torres, Armi G. - 11.03.03

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