Evaluation of characters of the digenean family Gymnophallidae Morozov, 1955

Abstract

Characters of the family Gymnophallidae are defined and evaluated to provide a better framework for cladistic analysis and a basis for determining its relationship with other families within the Strigeiformes. Gymnophallids are exclusively marine parasites that commonly use bivalve mollusks and rarely utilize gastropods and polychaetes as intermediate hosts. Marine birds are the final hosts, but human infections have recently been reported in Korea. Daughter sporocysts, cercarial and metacercarial germinal sacs, cercariae, and adults are stages of the life cycle. Depending on the season and species, furcocercous cercariae remain in the sporocyst or leave to find other bivalve or polychaete hosts. The metacercaria are found unencysted and in specific sites where they may cause pits in the shell, concretions, or pearls. Fossilized clams with pits are the first geological evidence of parasitism between digeneans and their hosts. Chick chorioallantoic membrane incubation of the metacercariae combined with scanning electron microscopy of adult gymnophallids can be useful in diagnostics. Seven genera of the family Gymnophallidae can be separated on the basis of 11 characters.