Euchonicola caudatus, Boxshall & O’Reilly & Sikorski & Summerfield, 2019

Boxshall, Geoff A., O’Reilly, Myles, Sikorski, Andrey & Summerfield, Rebecca, 2019, Mesoparasitic copepods (Copepoda: Cyclopoida) associated with polychaete worms in European seas, Zootaxa 4579 (1), pp. 1-69 : 52-54

Euchonicola caudatus gen. et sp. nov.

Type material: ♀ Holotype from Euchone sp., Regionale 2004, Stn 06-3 (60.5222°N, 03.727°E), depth 295 m, 0 1 June 2004; collected by A. Sikorski; NHMUK Reg. No. 2015.445. ♀ paratype from Euchone sp., Fish 2010, Stn 5- 4 (71.78508°N, 21.16853°E), depth 315 m, 23 May 2010; collected by A. Sikorski; NHMUK Reg. No. 2015.3011. ♀ paratype from Euchone sp., Snøhvit, Stn SF 9-2 (71.61494°N, 21.04817°E), depth 323 m, 0 9 June 2003; collected by A. Sikorski; NHMUK Reg. No. 2016.588. ♀ paratype detached from host, Euchone sp., northern North Sea , NW Hutton Field, BP x 0 54, 5000N (61.14501°N, 01.30915°E), depth 146 m, summer 2002; collected by P.R.Garwood; NHMUK Reg. No. 2015.3012.

Differential diagnosis. Adult female attached to host via short oral stalk connecting ectosoma with discoid, embedded endosoma ( Fig. 22 A–C). Total length of cylindrical ectosoma 406 to 443 µm, with trunk about 2.4 to 2.5 times longer than wide (365–410 µm by 160–165 µm, respectively); retaining apparent traces of subdivision along body ( Fig. 22A ) in some specimens, and with distinct abdomen. Stalk located anteriorly on ectosoma ( Fig. 22E ), with paired lobate antennules and subchelate antennae positioned close to base of stalk. Antennules ( Fig. 22F ) lobate, unarmed. Antennae ( Fig. 22G ) comprising broad basal segment with lobate inner margin, and strongly recurved, claw-like apical subchela: tip of subchela opposing rounded swelling on myxal margin of basal segment when adducted. Ectosoma bearing paired, unarmed, rounded genital lappets posteriorly, marking genital openings. Paired cement glands visible posteriorly in trunk, extending at least half length of trunk. Abdomen distinct, unsegmented, about 2.2 times longer than wide; bearing laterally-directed caudal rami, and with median anal slit ( Fig. 22D ). Caudal rami divergent; each ramus bipartite with broad proximal part and narrow distal part bearing vestige of single caudal seta apically ( Fig. 22D ). Egg sacs unknown.

Etymology. The name of the new species alludes to the bipartite state of the caudal rami of the adult female.

Remarks. The adult female of the new species has a cylindrical, unsegmented trunk bearing a distinct abdomen posteriorly. The trunk may show signs of subdivision but this probably reflects the presence of a series of relatively large eggs within the oviducts inside the trunk. The caudal rami are bipartite and strongly divergent in this species. Females of the new species occured on unidentified hosts of the sabellid genus Euchone Malmgren, 1866 collected from northern Norway and the northern North Sea. Off the coast of Norway, the parasite occurs in waters from 295 to 323 m in depth.

Figures

FIGURE 22. Euchonicola caudatus gen. et sp. nov. female. A, detached female, lateral view; B, same, ventral view; C, attached female (to setiger 8 of host), lateral view showing extent of endosoma drawn through cleared body wall of host; D, posterior extremity, showing divergent, bilobate caudal rami and anus; E, stalk; F, lobate antennule; G, antenna. Scale bars: A– C, 100 µm, D–G, 25 µm.