Pholoicola chambersae, 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 : 26-27

Pholoicola chambersae gen. et sp. nov.

Type material: Holotype ♀ and 2 paratype ovigerous ♀♀ from single Pholoe pallida Chambers, 1985 , Fram V, Stn A 2 5-5 (61.0884°N, 03.5091°E), depth 357 m, 0 4 June 2004; collected by A. Sikorski; NHMUK Reg. No. 2016.546 (Holotype on setiger 11 on right side) and 2016.547-548 (paratypes on setigers 25 and 33 on left side). 2 ovigerous paratype ♀♀ from 2 specimens of P. pallida , 4315 Loshavn, Stn 7-4 (57.6122°N, 06.604321°E), depth 172 m, 27 May 2008; collected by A. Sikorski; NHMUK Reg. No. 2016.549-550. 2 paratype ♀♀ from single P. pallida, Troll B, Stn 12-4 (60.7288°N, 03.664°E), depth 312 m, 0 2 June 2004; collected by A. Sikorski. NHMUK Reg. No. 2017.162. 3 paratype ♀♀ (1 ovigerous) from single P. pallida , 8690 Saltkjevika C, Stn Salt 3-2 (64° 35.909’N, 11° 16.572’E), depth 244 m, 0 5 January 2017; collected by A. Sikorski; NHMUK Reg. Nos 2017.163- 165.

Differential diagnosis. Adult female highly transformed and deeply embedded in host with only genitoabdomen protruding through body wall of host. Body length about 0.56 mm. Body bipartite ( Fig. 10A, B ) comprising large anterior part separated from narrower, tapering posterior genitoabdomen by deep furrow. Anterior part trilobate, with median frontal lobe and paired dorsolateral lobes; varying in size with reproductive state of female, maximum width about 0.6 mm. Genitoabdomen about 0.37 mm long, widest at origin on ventral surface of anterior part, narrowing gradually toward rounded posterior extremity, bearing paired genital apertures ventrally. Asymmetrical dorsolateral lobes present on genitoabdomen ( Fig. 10B ). Ovaries and paired oviducts located within embedded genitoabdomen. No vestiges of any limbs observed; caudal rami lacking; without anus. Egg sacs paired, subspherical ( Fig. 10C ), about 250 um in diameter; eggs about 80 µm in diameter.

Adult male mean body length 128 µm (range 122 to 135 µm, based on 4 specimens); comprising cephalothorax and ovoid post-cephalothoracic trunk ( Fig. 10D, E ); cephalothorax about 54 µm in width, deflected ventrally at angle to trunk ( Fig. 10D ); produced anteriorly into thickened rectangular frontal zone about 22 µm wide ( Fig. 10F ). Single pair of reduced cephalothoracic limbs present, located ventrolaterally on protruding frontal zone; each limb armed with short apical claw. Spermatophore sausage-shaped ( Fig. 10G ), about 50 µm long by 15 µm wide, with long slender sperm tube. Paired developing spermatophores visible within male ( Fig. 10D ), located anteriorly within cephalothorax and anterior part of trunk; containing elongate filiform sperm.

Final copepodid of male: antennule 5-segmented ( Fig. 10H ); setation 1, 5 + ae, 1, 2 + ae, 4 + ae. Antenna originating adjacent to base of antennule; comprising 2 slender segments plus slender apical claw ( Fig. 10I ). Maxilliped subchelate ( Fig. 10J ), comprising small syncoxa, robust basis and slender subchela consisting of unarmed proximal endopodal segment and second segment armed with inner seta and fused to terminal claw. Other features of copepodid stage unknown.

Etymology. The new species is named in honour of Sue Chambers, the discoverer of the only known host of this parasite.

Remarks. We did not find a complete copepodid stage but on several occasions males were associated with the extreme anterior end of the moulted final copepodid exuvium which had become trapped between the attached male and the female. The antennule was 5-segmented and its setation pattern, with large aesthetascs on segments 2, 4 and 5 is shared with Eurysilenium as figured by Lützen (1968). The segmentation of the maxilliped ( Fig. 10J ) of P. chambersae gen. et sp. nov. is the same as that found in the final copepodid stage of herpyllobiids: in both Herpyllobius arcticus (cf. Fig. 2D ) and Eurysilenium australis (see López-González et al. 2006) the subchela comprises two endopodal segments with the second fused to the terminal claw; the second segment is armed with an additional seta in E. australis and Pholoicola gen. nov. but this seta is lacking in H. arcticus .

The only known host is the pholoid Pholoe pallida and this is the first parasitic copepod to be reported from any member of the family Pholoidae . It is reported here from off the west coast of Norway between 57° and 64°N and its known depth range is 172 to 357 m. The females are typically embedded in the side of the host and the tip of the female genitoabdomen protrudes through the lateral body wall of the host between adjacent parapodia. The females are commonly attached in the mid-body region, but were found in positions ranging from setiger 6 to setiger 33.

Figures

FIGURE 2. Last male copepodid of Herpyllobius arcticus Steenstrup & Lütken, 1861 from female on Harmothoe fragilis. A, exuvium of last copepodid stage containing adult male (stippled), showing outline of spermatophores, dorsal; B, rostrum, ventral; C, antennule; D, maxilliped, E, leg 1 and intercoxal sclerite; F, leg 3 and intercoxal sclerite. Scale bars: A, 100 µm, B, D, 10 µm, C, E–F, 25 µm.

FIGURE 10. Pholoicola chambersae gen. et sp. nov. A, adult female with 3 males attached, ventral; B, female, dorsal; C, detached egg sac; D, adult male, lateral view showing position of developing paired spermatophores; E, adult male, ventral; F, cephalothorax of male, lateral view showing thickened frontal region and clawed limb; G, spermatophore; H, last male copepodid stage, antennule; I, antenna; J, maxilliped. Scale bars: A, 0.5 mm, B–C, 250 µm, D–E, 50 µm, F–H, 25 µm, I–J 10 µm.