SURVEY OF THE VARIATION IN ALAR AND MALAR THORNS IN SKATES - PHYLOGENETIC IMPLICATIONS (CHONDRICHTHYES, RAJOIDEI)

A total of 62 species, representing 24 of the 28 supraspecific taxa of skates, was surveyed for the presence, distribution, and structure of alar and malar thorns. The survey revealed that alar thorns are almos t universally present in mature male skates, and that malar thorns are of two types that may have separate origins. The location and orienta tion of alar thorns differed in two major clades of skates (groups I a nd II). They were either exposed on the disc with the crown oriented o bliquely to the long axis of the base or imbedded in slits in the inte gument and oriented parallel to the long axis of the base. Group I pos sessed the former type of thorns and, with several exceptions, group I I possessed the latter type. Group I either lacked malar thorns or pos sessed malar thorns that were most likely derived from generalized pla coid scales. Group II possessed, with several exceptions, malar thorns derived from enlarged placoid scales. Within group I the supraspecifi c taxa Atlantoraja and Rioraja possessed unique alar thorns that were reclined laterally and associated with lateral grooves in the integume nt. Within group II the supraspecific taxa Anacanthobatis, Cruriraja, Dipturus, Ohamejei, Raja, the North Pacific Assemblage, and the Amphi- American Assemblage had a large barb on the distal section of the crow n of the alar thorn that suggests that these taxa form a clade. The cr own of the alar thorns of the latter five supraspecific taxa was undul atory, thus supporting their monophyletic status. Another assemblage w ithin group II had ridges that ran most of the length of the crown of the alar thorns corroborating their monophyletic status. The survey al so suggested that variation of integumentary grooves associated with t he alar thorns in Bathyraja, and presence or absence of malar thorns i n Psammobatis, may be phylogenetically informative. (C) 1996 Wiley-Lis s, Inc.