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The Blind Electric Rays of the Genus Typhlonarke (Torpedinidae)

Typhlonarke tarakea Phillipps 1929; (Pl. 1, Figs. C, D, E, J. Text Figs. A, C, D.)

Typhlonarke tarakea Phillipps 1929; (Pl. 1, Figs. C, D, E, J. Text Figs. A, C, D.)

Study Material.—Male 266 mm. T.L., female 244 mm. T.L., female 206 mm. T.L. Collected by trawl from Cook Strait area.

Description.—Body greatly depressed, ovate in outline, tapering towards the peduncle. Skin smooth, lacking dermal denticles. Length of disc 1.4 in total length. Greatest width of disc at the level of the last two gill-slits, 2.0 in total length. Greatest depth of body at level of the last gill-slit, 7.5 in total length. Disc thinner peripherally but with a thick margin which is about 3.0 in the depth of the body. Caudal peduncle stout, slightly compressed.

Distance from anterior edge of disc to spiracles almost equal to the depth of body. Spiracles oval, their long axes directed outwards anteriorly. Eyes not visible externally, though a white patch anterior to each spiracle indicates their approximate position. Eyes very small, lying 2.0 mm. to 3.0 mm. below the surface of the skin in the subcutaneous fascia. Gill-slits small, crescentic. The first and fifth slits smaller than the others. Distance between first and second slits equal to that between fourth and fifth, and three-quarters to four-fifths of that between second and third or third and fourth. Nostrils very closely set, their posterior valves expanded and curled round, forming a nearly complete tube. Anterior nasal valves confluent as a fleshy nasal flap, slightly expanded distally and secured between the nostrils by a thick median septum, so that its wider free end almost covers the mouth. The extension of the nostrils and nasal flap makes a distinct step in the profile. Mouth small, slightly curved, and deeply inset, almost hidden externally by the nasal flap and the greatly enlarged, deeply incised lower lips. Teeth arranged in mosaic, 11/11 per row. Tooth plates very narrow, extending across the median part of the jaws, with four to five rows teeth functional. Teeth in the posterior rows each with a single median cusp, long and sharply pointed, directed posteriorly. Anterior teeth with cusps eroded so that in the first raw cusps are almost lacking.

One small dorsal fin originating slightly anterior to the posterior edge of the pelvics. Posterior edge rounded, extending behind the posterior insertion of the fin. Height of the fin 2.0 in its basis and 3.5 in the distance from anterior edge of disc to spiracles. Origin of the caudal just behind the posterior edge of the dorsal. page 6 Outline rounded except for two small indentations, one dorsal, the other posterior. Height of fin 1.5 to 1.8 in its length. Pectorals very thick, fused into the body so that the margin is a smooth curve. Paired electric organs present, reniform in shape, extending from midway between anterior edge of disc and eyes, back to the pelvic symphysis. The greatest width of each organ slightly less than one-third the width of the disc. Origin of pelvics not quite half of total length, from anterior edge of disc. Pelvics free anteriorly where they are produced into long finger-like appendages, which when appressed are directed acutely to the long axis of the body. Length of each appendage equal to distance from anterior edge of the disc to spiracles, width about 3.0 in their length. The posterior portions of the pelvics completely fused on to and extending the disc, but with no notch between them and the pectorals. Claspers rod-like, extending behind the posterior edge of the pelvics. Width of the claspers 2.0 in width of the appendage of the pelvic, and length 1.5 in the length of the same appendage. Cloacal aperture opposite the posterior insertion of the pelvic fin appendages.

Colour.—Brownish-black above. Periphery of disc and ventral surface light brown. Lips, nostrils, and lower surfaces of the free parts of the pelvics, white. Cloacal aperture and openings of the endolymphatic ducts ringed with white.

Size.—Most specimens taken are under 300 mm. in total length, though a specimen 362mm. long was trawled off Otago Heads (Hamilton, 1902).

Distribution.—Otago Heads; Cook Strait; down to 130 fathoms.

References and Synonymy.—Astrape aysoni Hamilton. A. (1902), Trans. N.Z. Inst., 34. Pls. X, XI, and XII Fig. a (T. tarakea, not T. aysoni). Typhlonarke tarakea Phillipps, W. J. (1929), N.Z. J. Sci. & Tech., 11. p. 101, Fig. 3. Whitley, G. P. (1940), Fishes of Australia, Part 1, p. 163, Fig. 185; Phillipps, W. J. (1949), Trans. Roy. Soc. N.Z., vol. 77, p. 289.