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The Blind Electric Rays of the Genus Typhlonarke (Torpedinidae)


Compared with other countries, the New Zealand elasmobranch fauna is relatively poor in both genera and species. It is all the more remarkable, then, that in the small number of skates and rays in these waters, there are two species of blind electric rays (Typhlonarke aysoni and T. tarakea). T. aysoni is a well-recognized species, but T. tarakea was regarded by Whitley (1940) as only a "nominal species" and has been omitted in Fowler's extensive account (1941). Elsewhere, blind electric rays are known from only two places, each with one species. Of these, Benthobatis moresbyi Alcock 1898 has concealed eyes and comes from deep water off Southern India, and Narke (Bengalichthys) impennis (Annandale 1909), which has minute sunken eyes and lives in shallow water in the northern part of the Bay of Bengal. Both our species are as specialized as Benthobatis. Morphologically both are poor swimmers. It is doubtful that the thick-disced T. tarakea could swim at all, and in this species is found the greater independence of the pelvic appendage. In both species, the radial muscles of the pelvics are more heavily represented, particularly on the free appendage, than in Torpedo fairchildi. The mouth is apparently suctorial. The eyes are concealed by uninterrupted smooth skin, but, unlike Benthobatis, our species are from shallow water.

The G. Typhlonarke was established by Waite (1909) to contain T. aysoni (Hamilton 1902). originally placed in the G. Astrape but distinct in the form of the disc, junction of the disc and pelvics, the absence of functional eyes, and the short tail. Phillipps (1929) recognized a second species, oval in form and remarkable in the absence of a dorsal fin. In 1949, Phillipps states that a specimen taken on a "foul hook" at 130 fathoms in Cook Strait had a dorsal fin. Examination of the type in the Dominion Museum shows a definite scar at the site of the dorsal. Phillipps also states, on the evidence of Professor B. J. Marples, that both species occur off Otago Heads. Hamilton's original account actually includes both species, but clearly a specimen of T. aysoni as recognized by Waite (1909) was the first examined and is the basis for the species. This specimen is shown in Plate XII, Fig. B. The other figures in Hamilton's paper refer to T. tarakea. The confusion of the two species rests in the absence of functional eyes and the form of other striking features which apparently detracted attention from the quite definite distinctions between the two. Both species are blind, shallow water, obviously benthic, and with quaintly modified pelvics; but T. aysoni is circular in outline, the margin of the disc is thin, and the claspers do not reach beyond the margin of the disc. T. tarakea has an ovoidal disc with a heavy thick rim, and the claspers are visible in dorsal view. Other features common to both species, and not mentioned page 2
Plate 1 (scale in cm.)

Plate 1 (scale in cm.)

A: T. aysoni, ventral view. B: T. aysoni, dorsal view. C: T. tarakea, dorsal view. D, E: T. tarakea. ventral views. F: Torpedo fairchildi, mouth and nostrils. G: T. aysoni, mouth and nostrils. H: T. aysoni, columns of electric organ in dorsal view. I: Torpedo fairchildi, columns of electric organ in dorsal view. J: T. tarakea, superficial dissection of dorsal surface of head region on left side, to show reduced eye.

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Text-figure 1 (scale in cm.)

Text-figure 1 (scale in cm.)

A: T. tarakea, lateral view. B: T. aysoni. lateral view. C: T. tarakea. tooth plate. upper jaw. D: T. tarakea, median teeth of first, third, and fifth rows, lower jaw. E. F: T. aysoni, median teeth of first, third, and fifth rows, upper and lower jaws.

Abbreviations: AP, pelvic fin appendage. BEO, boundary of electric organ. BL, lower lip. CEO, column of electric organ. CR, neurocranium. E, eye-ball. EM, ocular muscles, EO, electric organ. LLP, lateral line pore. LJ, lower jaw. LMX, m. levator maxillae. LR, m. levator rostri. MA. naris. NF, nasal flap. N.I I. optic tract. OED, opening of the endolymphatic duct. P. pedicel. ROS, r. ophthalmicus superficialis, SC, dorsal extension of the scapula. SP, spiracle. UJ, upper jaw. UL, Upper lip. WSP, anterior wall of spiracle.

by Waite in his generic description, are: the rostral cartilage, short and reduced to a median portion only; the anterior edge of the disc supported by greatly enlarged preorbital cartilages: the cranium lacks a formed orbit: the pectoral girdle extends as a complete ring around the vertebral column; on each side of the head there is a large electric organ, hounded medially by the trunk muscles and laterally by the propterygial elements: the columns forming the electric organ are very large, there being only 180 to 200 columns in each organ (Torpedo marmorata has about 450 columns per organ). Waite (1909) and Phillipps (1929) state that the eye is lacking in Typhlonarke though an optic nerve persists. Dissection of a number of specimens of both T. aysoni and T. tarakca shows (Plate 1, Fig. J) that the eye and optic nerve are present in both species, though the eye is not visible externally, being some 2.0 mm. under the surface of the skin in the subcutaneous fascia. Very delicate fibres inserted on the eyeball apparently represent vestiges of the ocular muscles.