Reintroduction of Profilicollis Meyer, 1931, as a genus in acenthocephala: significance of the intermediate host.

Polymorphid acanthocephalans with long necks, spheroid proboscides, and eggs without polar swellings of the fertilization membrane constitute a morphologically distinct group of species. In the past, this taxon was considered a separate genus, Profilicollis. More recently, workers have been unwilling to accept these features as generic-level characters, and presently the group is considered a subgenus of Polymorphus. An analysis prompted by our studies of various polymorphid cystacanths in crabs along the coasts of Scotland and the U.S.A. reveals that all records of Polymorphus in decapods refer to species with 6 cement glands frequently assigned to Hexaglandula, to incidental occurrences of species purported to be Polymorphus minutus, or to species of the subgenus Profilicollis. Occurrence in decapod crustaceans implies substantial life history differences from the other species of the genus occurring in amphipod crustaceans. We conclude this, together with morphological distinctiveness, justifies return of Profilicollis to full generic status within Polymorphidae.