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 duogland adhesive system. Three kinds of ciliated sensory receptors are described for the first time in Diuronotus. The filiform spermatozoon consists of an acrosome, a nuclearmitochondrial 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.

1. Gastrotricha

“…Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 6/16/15 1:05 PM When cuticular structures such as spines or scales are present ( Fig. In Diuronotus aspetos and Musellifer delamarei, the solid scales are made up of two electron-dense, homogeneous layers (Balsamo et al 2010a). Rieger & Rieger (1977) and Ruppert (1991) recognized three different types of such structures.…”

“…1.32 D and 1.37 G) and Muselliferidae are still hermaphrodites that develop full male and female gonads during their life history (e.g., , Guidi et al 2003a, Balsamo et al 2010a). Putative basal paucitubulatinan groups such as the marine Xenotrichulidae (Figs.…”

Record of the ‘Arctic’ marine gastrotrich Diuronotus aspetos (Paucitubulatina) from the southern North Sea

“…D. rupperti Todaro, Balsamo & Kristensen, 2005 is reported from a beach on the island Laesø, Denmark, while D. aspetos was recorded twice (in 1979 and 2006) from shallow sublittoral sand near the forsaken settlement Skansen on Disko Island, Greenland (Fig. 1g, Todaro et al 2005, Balsamo et al 2010. A third putative species of Diuronotus possibly inhabits sediments of the east coast of North America (Fig.…”

“…1b), a mouth with protrusible processes (Fig. 1c, see also Balsamo et al 2010), and pairs of long (37 μm) secondary and short (14.5 μm) primary adhesive tubes (Fig. 1a, d-f).…”

“…Both known species of Diuronotus are characterized by the possession of one pair of primary plus one pair of secondary adhesive tubes on their furcal appendages. Diuronotus and a second taxon, Musellifer, are both in the family Muselliferidae based on the shared presence of an elongate, ciliated snout-like region called the muzzle and the peculiar ultrastructure of their spermatozoa (Leasi & Todaro 2008, Balsamo et al 2010.…”