Discoleus Breure, 1978: is there a pre-Gondwanan ancient stock of Orthalicidae?

CUEZZO, M. G., VALDOVINOS, C. & BREURE, A. S. H.

BARILOCHE

Congreso; VI SOUTHERN CONNECTION CONGRESS; 2010

UNIVERSIDAD NACIONAL DEL COMAHUE

Discoleus Breure, 1978 is an endemic genus of southern South America. It is composed of two species, D. ameghinoi and D. aguirrei whose distributional areas are the most septentrional of Orthalicidae in Argentina. The genus Plectostylus, mainly distributed in Chile was believed to be Discoleus sister group and Bothriembryon of Australia was sister group of the former clade. Orthalicidae was known to be distributed in Australia and America but it was presumed to be of Gondwanan origin (Breure 1979; Solem 1998). The recently inclusion of the genus Prestonella from South Africa within this family confirmed the Gondwanan distribution of Orthalicidae (Herbert & Mitchell 2007, 2009). The aim of the present research is to provide a taxonomic revision of the genus Discoleus, a presumed component of the ancient stock of the Orthalicidae and a hypothesis of relationships with its related genera.  Discoleus is diagnosed by having a vas deferens embedded into the phallic complex along its length, lack of a cuff-like penial sheath, length of bursa copulatrix duct exceeding the spermoviduct length and secondary ureter open. Although both species of Discoleus have been previously classified in Bostryx, they are similar to Bostryx only by shell morphology. Preliminary cladistic analysis showed that Discoleus, Plectostylus, Prestonella and Bothriembryon conforms a monophyletic clade supported by four synapomorphies and with well Bremer support score. Herbert & Mitchell (2009) hypothesis on the Gondwanan prefragmentation stock is tested and discussed.