Introduction

Pterotrachea scutata is immediately distinguished from the other two species in the genus by the lateral expansion of the anterior portion of the trunk, forming a large cuticular disk. The eyes are rectangular in dorsal view, very similar to those in P. coronata. The visceral nucleus is relatively short, tear-drop shaped, similar to that in P. hippocampus, and markedly shorter than in P. coronata. Unique to the species is a wreath of two or three rows of peribuccal teeth located inside the mouth opening. Morphology of the central rachidian tooth on the radula is similar to that in P. hippocampus. The larva is unknown, but is probably either larva 2 or 3 of Richter (1968, see Pterotrachea larvae). The geographical distribution is cosmopolitan in tropical to subtropical waters.