CHRYSOPETALIDAE Ehlers, 1864

Watson, Charlotte & Faulwetter, Sarah, 2017, Stylet jaws of Chrysopetalidae (Annelida), Journal of Natural History 51 (47 - 48), pp. 2863-2924 : 2869-2870

Family CHRYSOPETALIDAE Ehlers, 1864

Subfamily CHRYSOPETALINAE Ehlers, 1864

Subfamily diagnosis

Small to large bodied; body relatively short compared to number of segments; segments short and close together; flattened to very slight convex dorsum covered in imbricating notochaetal paleal fans (some taxa with additional spines). Flat ventrum, some taxa with segmental ventral pads. Prostomium free or fused with anterior segments: with complex eyes (absent in deep-sea taxa), median antenna, lateral antennae and palps well developed (latter two structures differentiated). External, protrusible nuchal organs (caruncle or nuchal fold) present. Strongly muscularized ventral pharynx with well-developed proboscis (calcification may be present), terminal papillae, stylet jaws, ventral mouth cover. Dorsal and ventral cirri on each segment (ventral cirri absent on 2nd segment in some taxa). Camerate simple paleal notochaetae and camerated shafts of compound neurochaetae; simple spines may be present in notopodia and neuropodia. Body with segmental ciliation, lateral organs; complex nervous system and complex body wall musculature present. Pygidium quadrate or conical with two anal cirri.

Remarks

Ehlers (1864, p. 80) offered brief diagnoses of the family Chrysopetalidae and the type genus Chrysopetalum . Compilation and translation comprises: ‘prostomium with eyes, 3 antennae and 2 palps; segment 1 with 4 tentacular cirri; each dorsal segment with cirri and paleae’. The diagnosis in the present paper constitutes the first full diagnosis of the subfamily, Chrysopetalinae , and is based in part on descriptions of the Chrysopetalidae ( Watson Russell 2000b; Rouse and Pleijel 2001) and on Aguado et al. (2013) who nominated, but did not formally describe, the subfamilial rank of Chrysopetalinae for the paleate clade within the family.

Chrysopetalinae taxa comprise marine, free-living, gonochoristic species living predominantly in hard substrates from deep-sea hydrothermal vents to shallow coral reefs. Larval studies indicate planktonic, lecithotrophic larvae ( Cazaux 1968; Blake 1975; Watson et al. 2014). Notochaetal paleae enable protection and camouflage: they are non-pigmented and can appear transparent but also reflect all shades of silver/gold/bronze, according to species, e.g. Arichlidon ( Figure 1a ). Camerate notochaetal paleae and neurochaetal shafts confer lightness and strength and are present in larvae and adults ( Westheide and Watson Russell 1992; Watson et al. 2014). Epitokous swimming chaetae have been described for Arichlidon species ( Watson Russell 2000a).

Sensory structures include a single median antenna, two lateral antennae, welldeveloped eyes and palps, external nuchal structures and lateral organs. Retractile structures are evident in certain taxa: anterior segments in conjunction with the nuchal fold (e.g. Paleaequor ; Watson Russell 1986); retractile styles of the dorsal cirri (e.g. Bhawania ; Watson Russell 2000b); retractile distal tips of palps (e.g. Thrausmatos ; Watson 2001) or pits at distal tips of palps (e.g. Chrysopetalum ; Watson 2001; Watson and Chatzigeorgiou, Forthcoming, and Acanthopale ; CW pers. obs.). Pharyngeal structures include a mouth flap, terminal proboscidial papillae and diverse-shaped buccal organs and stylets (see individual taxon treatments below; Tables 1 and 2). Musculature ( Storch 1968), ultrastructure of the body wall ( Tzetlin et al. 2002) and the nervous system (Beckers, pers. comm.) are described as ‘complex’.

Figures

Figure 1. Live photos: (a) Chrysopetalinae. Arichlidon gathofi Watson Russell, 2000a (~5 mm L); (b) Dysponetinae. Dysponetus pygmaeus (~3 mm L); (c–e) Calamyzinae: (c) free-living Micospina aureobohnorum Watson et al., 2016 (~4mm L); (d) ectoparasite Calamyzas amphictenicola (~ 2 mm L); (e) symbiont Shinkai longipedata (~ 250 mm L). Copyright: a, c, e: © Greg Rouse; b: © Monika Kedra/ Slawomira Gromisz; d: © Fredrik Pleijel. All photos reproduced with permission by the copyright holders.