Body-wall musculature of Praeconvoluta tornuva n. sp. (Acoela, Platyhelminthes) and the use of muscle patterns in taxonomy

Musculature of lower worms such as the acoel turbellarians can be readily r evealed with fluorescence microscopy and phalloidin-linked fluorescent dyes . In a new species of acoel, the meshwork of body-wall muscles could be res olved using BODIPY 558/568 phalloidin into four sets of fibers: (1) circula r muscles that encircle the body; (2) longitudinal muscles, most of which c ross over the body midline, having longitudinal orientation only in the ant erior third of the body and bending medially to the opposite lateral side o f the body more posteriorly; (3) a few diagonal muscles on the anterior dor sal body wall; and (4) special muscles that fan from pores (mouth and genit al pore). Compared to patterns of musculature in other acoels that have bee n studied, that of this new species shows characters that link it with spec ies of the Convolutidae as distinct from other acoel groups and characters that appear to be specific to it at the genus or species level. Such charac ters could well serve as diagnostic features of taxa of the acoels, which, as soft-bodied worms, are otherwise rather poor in distinctive features.