Diuronotus aspetos (Gastrotricha): New morphological data and description of the spermatozoon

Abstract

The genus Diuronotus (Gastrotricha Chaetonotida) includes two species, D. aspetos and D. rupperti; its morphological affinity with the genus Musellifer has been pointed out. Here, new morphological data from light and electron microscopy and the description of the spermatozoon of D. aspetos are reported, with the aim of clarifying the phylogenetic position of the genus. The mouth cavity has a wreath of stout, protrusible processes. The two secondary furcal tubes are inserted ventrally and are covered with elongate scales. All the caudal tubes contain a duo-gland adhesive system. Three kinds of ciliated sensory receptors are described for the first time in Diuronotus. The filiform spermatozoon consists of an acrosome, a nuclear-mitochondrial complex, and a flagellum. The acrosome including two long and different cones, the single, giant mitochondrion surrounding the nuclear base, and the axoneme arising from a deep nuclear 'fossa' appear as autapomorphic characters. The keeled, solid cuticular body scales and the spermatozoon with a supernumerary membrane are features shared with Musellifer delamarei. The structure of the accessory fibres is a strong spermatological similarity between the families Muselliferidae and Xenotrichulidae. Thus morphological and spermatological characters support the inclusion of D. aspetos and M. delamarei into the family Muselliferidae recently described. The comparative spermatology also suggests that Xenotrichulidae may be the sister group of Muselliferidae. © Springer-Verlag and AWI 2009.