Musculature of the facultative parasite Urastoma cyprinae (Platyhelminthes)

Tn an effort to understand how the feeding motions of Urastoma cyprinae are generated, the arrangement of its musculature was studied using fluorescen ce microscopy of phalloidin-linked fluorescent stains and conventional ligh t histology and transmission electron microscopy. BODIPY 558/568 phalloidin and Alexa 488 phalloidin resolved a meshwork of ribbon-shaped body-wall mu scles as well as inner-body musculature associated with the pharynx and mal e copulatory organ. The general pattern of body-wall muscles in U. cyprinae is similar to that of other rhabdocoel turbellarians in consisting only of circular, longitudinal, and diagonal fibers; the arrangement of these musc les readily correlates with the bending motions the animal undergoes as it feeds at the surface of gills in bivalves it parasitizes. The orogenital at rium of U. cyprinae lies at the posterior apex of the body, opening at a te rminal pore. As evidenced by the arrangement of its epithelium and musculat ure, it appears to be an invagination of the body wall and comes closest of any such duct studied in turbellarians to satisfying the hypothetical mode l of a "pseudopharynx," ostensibly adapted as an organ for swallowing and s o supplementing the ingestive role of the animal's true pharynx. J. Morphol . 241:207-216, 1999. (C) 1999 Wiley-Liss, Inc.