Dysponetinae Aguado, Nygren and Rouse 2015

Subfamily DYSPONETINAE Aguado, Nygren and Rouse, 2015

Subfamily diagnosis

Very small to small bodied. Prostomium well developed or simple lobe; with lateral and median antennae, ventral palps; eyes present or absent; nuchal structure ciliated dorsolateral patches. Strongly muscularized pharynx with little proboscidial development, terminal proboscidial papillae, pair of stylet jaws; mouth cover absent, buccal cirri may be present. Notochaetal spines; neurochaetae compound, neurochaetal simple spines may be present. Camerate noto- and neurochaetal shafts. Simple body wall musculature. Body ciliation and lateral organs absent. Pygidium rounded with conical projection.

Remarks

Diagnosis is based on Aguado et al. (2015) with additional information by senior author (CW). Dysponetinae comprise free-living species belonging to Dysponetus Levinsen 1879, a speciose genus exhibiting the most extensive geographical and depth ranges of all taxa within the family Chrysopetalidae. The subfamily also includes Pseudodysponetus Böggemann, 2009, a monotypic deep-water genus (Böggemann 2009, p. 291, figure 27A). Its type material was examined by CW (HZM D.25012). This taxon is very small, possessing aberrant anterior segments and a pair of very small stylets. The tanned, simple elongate jaws with a small mid-way swelling are similar to the simple rod-like pair of stylets, as seen in Dysponetus species.

Dysponetus displays alternative morphological states of sensory structures of the anterior end (see below) but lacks complex body wall musculature and ciliated and glandular fields (Tzetlin et al. 2002). Dysponetus macroculatus Dahlgren, 1996 and Dysponetus populonectens Pleijel, Aguado and Rouse, 2012 have been reported as gonochoristic and Dysponetus pygmaeus Levinsen, 1879 as a protrandic hermaphrodite with filiform sperm (Tzetlin et al. 2002). Males of Dysponetus pygmaeus and other particularly small species (e.g. Dysponetus bipapillatus Dahlgren, 1996 and Dysponetus ovalisetosus Darbyshire and Brewin, 2015) exhibit copulatory organs. Epitokous swimming neurochaetae in Dysponetus caecus (Langerhans, 1880) have been reported by Watson et al. (2014) and Dysponetus cf. pygmaeus larvae have been recorded from the plankton (Watson Russell 1987).