ELECTRIC ORGANS IN SKATES - VARIATION AND PHYLOGENETIC SIGNIFICANCE (CHONDRICHTHYES, RAJOIDEI)

A total of 63 species of skates (Chondrichthyes: Rajoidei) were survey ed, along with three species of the outgroup (Chondrichtyes: Rhinobato idei) for electric organs along the sides of the tail. All skate speci mens examined possessed what appeared to be functional electric organs , and the three species of the outgrpup lacked evidence of electric or gans. The electric organs were tail-positive and arranged into horizon tal columns divided by transverse septa. The electrocytes varied consi derably within and among supraspecific taxa (subgenera and genera), bu t they could be broadly classified into cup-shape, modified cup-shape, intermediate-shape, and disc-shape cells, provided that the distincti on was partially based on position of the electrocytes within their co nnective tissue chambers. The survey, in part, corroborates a phylogen etic hypothesis of skates and in some respects further resolves the hy pothesis. The supraspecific taxa Atlantoraja and Rioraja have similar derived-type electrocytes, as do the five supraspecific taxa of Rajini , and Cruriraja and Anacanthobatis, and to a lesser extent the suprasp ecific taxa Arhynchobatis, Psammobatis, and Sympterygia, and the supra specific taxa Notoraja, Pavoraja, and Pseudoraja, corroborating the hy pothesis. The supraspecific taxa Amblyraja, Rajella, Leucoraja, Brevir aja, and Dactylobatus were unresolved in the phylogenetic hypothesis, but the electrocyte survey suggested that Leucoraja, Breviraja, and Da ctylobatus were derived with respect to Amblyraja and Rajella. (C) 199 4 Wiley-Liss, Inc.