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.
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.
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.