Euchonicoloides halli, 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 : 57-60

Euchonicoloides halli gen. et sp. nov.

Type material: Holotype ovigerous ♀ attached to Jasmineira caudata Langerhans, 1880 , (Unico. 40916), Gardline , Stn ENV05-FB (approx. 44.75°N, 01.78°W), depth 110 m, Acquitaine Basin, Bay of Biscay, 0 4 May 2007; NHMUK Reg. No. 2015.2995.

Differential diagnosis. Ectosoma of holotype contracted showing apparent segmentation of trunk ( Fig. 25E ): about 230 µm in length (measured in dorsal view) with maximum width of about 175 µm. Ectosoma comprising large cephalothorax, 4-segmented postcephalic trunk and vestigial abdomen ( Fig. 26A, B ). Cephalothorax about 103 µm long (in dorsal midline) with maximum width of 175 µm, comprising about 45% of total body length, viewed dorsally. Cephalothorax attached to host via short stalk. First to third trunk somites all short and of similar width in dorsal view ( Fig. 25E ). Fourth trunk somite defined by suture dorsally but fused to third somite ventrally. Paired genital apertures present either side of vestigial abdomen ( Fig. 26A ). Abdomen represented by rounded lobe in posterior midline, lacking caudal rami and without anal slit. Egg sacs incomplete in holotype, more than twice as long as ectosoma; egg arrangement irregularly biseriate ( Fig. 25E ). Antennules absent. Antenna comprising broad basal part with curved digitiform distal part functioning as anteriorly-directed subchela ( Fig. 26A ). Endosoma lobate ( Fig. 26B ), smaller than ectosoma.

Etymology. The new species is named in honour of David Hall (formerly of Unicomarine Ltd., now at Apem Ltd.), who found this material and, over the years, has collected numerous parasitic copepods and kindly made them available for study.

Remarks. The new species is placed in Euchonicoloides gen. nov. because it shares with the type species, E. elongatus gen. et sp. nov., the derived form of the ectosoma in which the abdomen is fully fused to the trunk, and the lack caudal rami and an anal slit. In addition, no traces of antennules are present, whereas lobate antennules are found in the three new species of Euchonicola gen. nov. described above.

Euchonicoloides halli gen. et sp. nov. differs from the type species in having a short, squat ectosoma which expresses traces of body segmentation in both dorsal and ventral views. In addition, the form of the egg sacs is different, with a uniseriate arrangement of eggs in the type species but an irregularly biseriate arrangement in E. halli gen. et sp. nov. The only paired limbs present in adult females of Euchonicoloides gen. nov. are the antennae: in the type species they are subchelate with a clearly defined claw (cf. Fig. 25B ) whereas in E. halli gen. et sp. nov. they comprise a broad basal part with a curved digitiform distal part ( Fig. 26A ) with the latter apparently functioning as subchela used to attach to host.

The holotype and only specimen was attached in the mid-body of its host, a tiny (3 mm body length) specimen of the sabellid Jasmineira caudata caught in the Bay of Biscay.

Another mesoparasite, Jasmineiricola mackiei Boxshall, O’Reilly, Sikorski, & Summerfield, 2015 occurs on the same host species in waters around Norway, Sweden, the United Kingdom and Ireland. It bears only a superficial resemblance to Euchonicolides gen. nov. and differs in having a large anvil-shaped endosoma with a clearly defined head region and a trunk region with large lateral lobes. There is only a relatively small ectosoma comprising the tip of the genitoabdomen.

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.

FIGURE 26. Euchonicoloides halli gen. et sp. nov. Holotype. A, female holotype, ventral showing paired bifurcate limbs (?antennae); B, female holotype, lateral showing embedded endosoma. Scale bars: A–B, 100 µm.