What does the pelvic fin do to the fin?

Pelvic fins play a role in stabilization of the body during swimming. The bony fish pelvic fin is simple and is supported on a flat-lying triangular plate, somewhat similar to that of the female of the shark Falcatus. Pelvic fins of all sexually mature male chondrichthyans, however, also feature extensions of the fin axis that form sperm conducting ducts for internal fertilization of females. These paired structures, the claspers, are characteristic of adult male Chondrichthyes.
Chondrichthyans related to the modern chimaeroids also develop a tall dorsal process and a specialized first radial armed with denticles (pre-pelvic tenaculum), as seen in a relatively primitive state in Echinochimaera snyderi.