Meeting Abstract

P2.208  Saturday, Jan. 5  A new lithophoran proseriate with inverted genital pores from the New England coast LAUMER, CE*; GIRIBET, G; CURINI-GALLETTI, M; Harvard University; Harvard University; Università degli Studi di Sassari claumer@oeb.harvard.edu

Although the phylogenetic relationships of the diverse flatworm clade Proseriata have been the subject of recent attention, the frequent discovery of new proseriate species and higher taxa continues to evince unfamiliar characters and character combinations, with potentially meaningful systematic implications. Here, we present the unusual morphology of a new proseriate from coastal waters of New England. The large worms resemble members of the lithophoran families Coelogynoporidae and Calviiridae in many respects, e.g. the presence of paracnida, the vertical collar-shaped pharynx, the short common female duct, and the presence of distinct male and female gonopores. However, the inverted topology of their genital system is unique within Proseriata, presenting an anterior female pore shortly behind the mouth and a male pore opening nearly at the caudal terminus, permitting inclusion into neither family on morphological grounds. To discern the species’ systematic position relative to other Proseriata for which molecular data were available, we undertook analyses of its 18S and 28S rRNA sequences under diverse alignment conditions and optimality criteria. However, the phylogenetic position of the taxon proved remarkably unstable, particularly with respect to the method of alignment: analyses using a structural alignment place it as sister to the remaining Lithophora (with complete support), whereas a similarity-based alignment suggests inclusion within Coelogynoporidae (with poor support), while direct optimization yields a position sister to Calviriidae (with poor support). Given its unique morphology, as well as the limited (and conflicting) evidence for its inclusion within any family as currently defined, these worms may be best accommodated in a new, monogeneric family, the exact phylogenetic position of which must be the subject of further inquiry.