HOOGE, M.D.*; TYLER, S; The University of Maine, Orono; The University of Maine, Orono: Concordance of molecular and morphological data: The example of Acoela

Morphological features of the Acoela appear to be quite plastic, including those of the copulatory organs, which provide the principle characters used for the systematics of this group. Consequently, classification schemes of the Acoela comprise numerous polyphyletic groupings. In this review, we detail our revision of acoel systematics using molecular sequence data in the 18S rDNA gene and new and re-evaluated morphological characters. Gene trees are discordant with traditional systematic schemes but strongly concordant with newly obtained morphological characters, namely, ultrastructural characters of sperm and characters obtained through confocal microscopy of musculature in the body-wall and male copulatory organs. This merger of molecular and morphological data has led to significant changes to acoel classification, including a major emendation of the largest family of the Acoela, the Convolutidae, wherein half of its members are transferred to a newly erected family, the Isodiametridae.