Meeting Abstract

P3.175A  Friday, Jan. 6  New and useful knowledge on the genus Gnosonesima (Platyhelminthes: Neoophora) LAUMER, C.E.*; SMITH, III, J.P.S.; GIRIBET, G.; Harvard Museum of Comparative Zoology; Winthrop University; Harvard Museum of Comparative Zoology

Gnosonesima is a monogeneric taxon of rare meiofaunal Platyhelminthes known largely from (sometimes very deep) marine subtidal sediments. Most of the six known species are described from one or two specimens, or only an illustration. They nonetheless comprise a higher taxon within Platyhelminthes (Gnosonesimida sensu Karling 1968), and much interest has thus been expressed in the functional and phylogenetic significance of their unusual character systems (e.g., monocellular ocelli/tangoreceptors, genito-intestinal connections, "coniform" pharynx, and tetrapartite germovitellaria). We present the anatomy of four undescribed species of this taxon, the first to be reported from the Americas. Using live observations, HD video recordings, semi-thin histological sections, and confocal laser scanning microscopy, we demonstrate that these newly discovered species evince a number of dramatic departures from the anatomy of the known representatives. These include stably di- or tri-partite germovitellaria, a flattened or miniaturized body habitus, and several new types of male copulatory organs, including two forms sharing a conical sheath of sclerotic spines reminiscent of types known from other basal Neoophora (e.g., Prorhynchida, Proseriata). It is tempting to consider that these new morphologies may shed light on the plesiomorphic character states of Gnosonesimida. However, the discovery of such deviant species also implies that sampling of Gnosonesima and its relatives remains superficial. Thus, pending the discovery of further forms, and a phylogenetic analysis of the total group, we adopt an agnostic view on such questions of character evolution. For practical reasons, we recommend presently that these new species be accommodated in the classical genus Gnosonesima via an amended definition of the taxon.