A KARYOTYPIC STUDY OF THREE SPECIES OF RAJIFORMES (CHONDRICHTHYES, PISCES)

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Abstract
A karyotypic study has been made of three species of Chondrichthyes of the order Rajiformes: the lesser electric ray (Narcine brasiliensis) of the Torpedinidae, and two stingrays, the Atlantic stingray (Dasyatis sabina) and the bluntnose stingray (Dasyatis sayi) of the Dasyatidae. The karyotypes were derived by a squash technique from gill epithelial cells after specimen injection with colchicine. The lesser electric ray has a diploid number of 28 (18 m, 4 sm, and 6 st), the smallest diploid count yet discovered in the Chondrichthyes. Both stingrays have a diploid count of 68. The Atlantic stingray has 28 m-sm and 40 st-t,; the bluntnose stingray has 34 m-sm and 34 st-t. The suggestion is made that these species may show a relationship to skates previously described in that they possess a similar number of chromosome arms. A preliminary note is made on the chromosome number of the Atlantic guitarfish.

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