Are the genera of Nematomorpha monophyletic taxa?

Abstract

Twenty‐two genera of horsehair worms (Nematomorpha) have been described to date, one (Nectonema) from the marine environment and the remaining ones (taxon Gordiida) from freshwater. The aim of this investigation was to test whether the genera represent monophyletic taxa or are likely to be paraphyletic assemblages. The recognition and delimitation of monophyletic taxa are prerequisites for further systematic analyses. From the 15 nematomorph genera containing more than one species, autapomorphies can be found for five genera (Chordodes, Nectonema, Beatogordius, Acutogordius, Noteochordodes). In three further genera (Paragordius, Parachordodes, Gordionus), the evaluation of characters as autapomorphies is likely, but relies on further investigations. For seven genera (‘Gordius’, ‘Paragordionus’, ‘Euchordodes’, ‘Neochordodes’, ‘Pseudochordodes’, ‘Spinochordodes’, ‘Digordius’), no autapomorphy could be found. Five genera (‘Digordius’, Lanochordodes, Progordius, Pantachordodes, Pseudogordius) are likely to be synonymous with other genera, and one genus (Chordodiolus) has been synonymized with Beatogordius recently. The importance of high quality documentation of characters in investigations of nematomorph species is stressed.

Morphological and molecular characterization of Gordionus alpestris (Nematomorpha) from the North-West Caucasus, Russia

“…Mid-body diameter (MBD) was measured under a dissecting microscope on specimens in water. The terminology for morphological features of nematomorphs was used according to Schmidt-Rhaesa (2002). The measurements are presented in the text as the value for the voucher specimen and values for additional specimens (in parentheses).…”

The collection of Nematomorpha in the Zoological Museum Hamburg, including description of a new species, Chordodes jelkae sp. n.

“…The two specimens (I) and (II) both belong to the genus Paragordionus, because they possess clusters of megareoles (see Schmidt-Rhaesa 2002a). In specimen (II) the clusters of megareoles are smaller and include maximally three megareoles (Fig.…”

“…Species in this genus have two types of areoles, the second, larger type are large areoles that seem to be fusion products of several smaller areoles (Schmidt-Rhaesa 2002a, 2013. They are called superareoles.…”

“…The larger areoles are clustered together, such clusters can be composed of two or of several areoles. The large areoles are called megareoles (see Schmidt-Rhaesa 2002a, 2013, Schmidt-Rhaesa and Wagner 2013. Only five species have been described, and species limits require further investigations (Schmidt-Rhaesa and Wagner 2013).…”

South American species of Paragordius Camerano, 1897 (Gordiida, Nematomorpha), with redescription of Paragordius minusculus and a description of a new species

“…The cuticle varies between different species being able to form transverse irregular cords with knoblike structures on top (Schmidt-Rhaesa et al 2003) or with poorly defined, shallow areoles (de Villalobos et al 2001). Areoles are cuticular structures in compartments which may be flat, polygonal or more elevated and elaborated (Schmidt-Rhaesa 2002).…”