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Invertebrate Systematics Invertebrate Systematics Society
Systematics, phylogeny and biogeography
RESEARCH ARTICLE

Prosogynopora riseri, gen. et sp. nov., a phylogenetically problematic lithophoran proseriate (Platyhelminthes : Rhabditophora) with inverted genital pores from the New England coast

Christopher E. Laumer A C , Gonzalo Giribet A and Marco Curini-Galletti B
+ Author Affiliations
- Author Affiliations

A Museum of Comparative Zoology & Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA.

B Dipartimento di Scienze della Natura e del Territorio, Sezione di Zoologia, Archeozoologia e Genetica, University of Sassari, via F. Muroni 25, 07100 Sassari, Italy.

C Corresponding author. Email: claumer@oeb.harvard.edu

Invertebrate Systematics 28(3) 309-325 https://doi.org/10.1071/IS13056
Submitted: 8 November 2013  Accepted: 26 March 2014   Published: 30 June 2014

Abstract

A new lithophoran proseriate flatworm, Prosogynopora riseri, gen. et sp. nov. (Platyhelminthes: Rhabditophora: Proseriata), is described from the New England coast (USA). The species shares characters with members of the families Calviriidae and Coelogynoporidae, e.g. the presence of paracnida, the short common female duct, a septum and diaphragm at the base of the pharynx. However, the inverted topology of the genital system, presenting an anterior female pore shortly behind the mouth and a male pore opening nearly on the caudal terminus, is unique within the Proseriata, and permits inclusion into neither family on morphological grounds. We investigated the phylogenetic position of the new species within the available diversity of proseriate 18S and 28S rRNA sequences. However, an exploration of diverse homology schemes, alignment conditions and optimality criteria proved the position of P. riseri, gen. et sp. nov. to be remarkably unstable, particularly with respect to the method of alignment, variously suggesting sister-group relationships with (or within) Coelogynoporidae, with Calviriidae, or with a clade composed of all other Lithophora. Despite its unique morphology and the absence of molecular phylogenetic evidence for its inclusion within any family as currently defined, we refrain from assigning a higher taxonomic rank to the new lineage, pending critical re-assessment of homology in several character systems and the availability of further taxon- and gene-rich enquiries into the phylogeny of Proseriata. Apingospermata, new taxon and Dolichogynoducta, new taxon are proposed as two rankless taxonomic names of Lithophora, corresponding to well-supported clades in our molecular phylogenetic hypothesis.


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