The principal caudal fin ray count ‐ a fundamental character in the galaxioid fishes

Abstract

The principal caudal rays, usually defined as the two largest segmented unbranched fin rays in the caudal fin that lie above and below, and the segmented branched caudal rays that they enclose, have a consistent relationship to the caudal skeleton in galaxioid fishes, being those fin rays supported by the primitively ventral surface of elements in the caudal skeleton. They comprise rays supported by skeletal elements including, and posterior to, the parhypural and hypurals. The most anterior (or ventral) principal ray is supported by the parhypural while the posterior (or uppermost) principal ray lies immediately below the point at which the notochord emerges from the truncated posterior end of the last caudal vertebra. The consistent relationship to these skeletal elements suggests that the principal caudal fin ray count is a character of fundamental nature for the galaxioid fishes, giving it particular phylogenetic significance in that group.