Morphology of the presoma of Corynosoma hamanni (Acanthocephala: Polymorphidae)

A morphological study of the presoma of adult Corynosoma hamanni (Linstow, 1892) was undertaken in an effort to clarify some problems encountered during analysis of a large collection of juveniles of this species assembled from fishes of McMurdo Sound. This study is based on approximately 600 adult specimens recovered from four Weddel seals, Leptonychotes weddelli, collected at McMurdo Sound. Morphologically the proboscis armature is more varied than previously reported and consists of 18 to 23 longitudinal rows each with 11 to 15 hooks of two distinct types. At the apex of the proboscis is an undivided, bi‐nucleated apical organ unlike that described for species of Neoechinorhynchus. In the basal third of the proboscis is a thin‐walled vesicle which extends into the anterior quarter of the proboscis receptacle. The more posterior of two external folds on the presoma is a cuticular invagination permitting recognition of the neck‐trunk border of C. hamanni. Lemnisci originate between the two folds and extend into the trunk cavity between the body wall and extensive neck retractor muscles. Contrary to Linstow's original description, each lemniscus is a single structure. Several limitations in material prevent speculation at this time about the limits of intraspecific variation in C. hamanni.