Euchonicoloides elongatus, 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 : 57

Euchonicoloides elongatus gen. et sp. nov.

Type Material: Holotype ovigerous ♀ from Euchone sp., Mareano 2010110, Stn 556 (70° 38.38’N, 19° 23.8’E), depth 281 m, 0 4 August 2010; collected by A. Sikorski; NHMUK Reg. No. 2015.524 . Paratype ovigerous ♀ from Euchone sp., Mareano 2010110, Stn 613 (70° 46.23’N, 20° 49.88’E), depth 246 m, 19 September 2010; collected by A. Sikorski; NHMUK Reg. No. 2015.444 . Paratype ovigerous ♀ from Euchone sp., Snorre B 0 2, Stn 7-1 (61.52516°N, 02.247374°E), depth 355 m, 29 May 2002; collected by S. Gagaev; NHMUK Reg. No. 2015.443 .

Differential diagnosis. Female body comprising elongate ectosoma connected via short, broad stalk to small discoid endosoma embedded within host ( Fig. 25A ). Ectosoma unsegmented, more or less cylindrical, about 6.2 to 6.3 times longer than wide: length of ectosoma 458 to 528 µm (based on 3 specimens); maximum width 76 to 84 µm. Paired cement glands slender, about 165 µm in length, extending through posterior third of trunk only. Stalk broad, located anteriorly on ectosoma ( Fig. 25A, B ). Endosoma discoid, narrower than width of trunk; with well defined edges ( Fig. 25D ). Antennules absent. Antennae positioned posterolateral to base of stalk; comprising robust basal segment and curved apical claw ( Fig. 25B, D ). Cement glands paired, extending anteriorly to reach about to middle of ectosoma. Genital apertures paired, located posterolaterally on trunk. Abdomen reduced to rounded lobe fully fused with trunk and located dorsally in middle of posterior margin ( Fig. 25C ); no anal slit present and caudal rami lacking. Egg sacs uniseriate, with up to 10 spherical eggs ( Fig. 25B ).

Etymology. The name of the new species refers to its elongate ectosoma, which is more than six times longer than wide.

Remarks. All three of the available specimens carried a single egg sac and the only intact egg sac contained 10 eggs. The eggs were arranged in a single series but the eggs are more or less spherical, not discoid as in caligiform copepods. This parasite is embedded in the head of its host so its egg sacs extend out with the tentacles of the host. Its elongate, cigar-shaped ectosoma which incorporates the abdomen, serves to distinguish this species from its congener described below.

This species is known only from females found on unidentified specimens of the sabellid genus Euchone collected at depths between 246 and 355 m off the coast of western and northern Norway.

Figures

FIGURE 25. Euchonicoloides elongatus gen. et sp. nov. female. A, ovigerous female, ventral; B, anterior part of ectosoma, stalk and endosoma, ventral view showing position of subchelate antennae; C, posterior part of ectosoma, ventral view shwoing extent of cement glands; D, stalk and antenna, lateral. Euchonicoloides halli gen. et sp. nov. Holotype. E, habitus of ovigerous holotype, dorsal. Scale bars: A, E, 100 µm, B–D, 50 µm.