Haplostoma gracile, Kim & Boxshall, 2021

Kim, Il-Hoi & Boxshall, Geoff A., 2021, Copepods (Cyclopoida) associated with ascidian hosts: Ascidicolidae, Buproridae, Botryllophilidae, and Enteropsidae, with descriptions of 84 new species, Zootaxa 1, pp. 1-286 : 145

Haplostoma gracile sp. nov.

(Fig. 93)

Type material. Holotype ♀ (MNHN-IU-2018-1994, as a whole mount on a slide) from ieptçclẚnẚdes sp.; New Caledonia, no other collection data.

Etymology. The name is derived from the Latin gracẚl (=slender), referring to the elongate, vermiform body of the new species.

Description of female. Body (Fig. 93A) extremely elongate, vermiform, straight, consisting of unsegmented trunk and small abdomen. Body 11 times longer than wide; length 3.25 mm and maximum width 286 μm, across region of leg 3. Cephalosome (Fig. 93B) obscurely defined from and narrower than metasome. Intervals between first to fourth legs 409, 614, 764 μm, respectively; distance from leg 4 to posterior tip of urosome 1182 μm. Genital apertures not seen. Abdomen (Fig. 93C) small, slightly longer than wide (116×103 μm), incompletely articulated from metasome, lacking any trace of segmentation, slightly narrowing posteriorly, with convex rear margin. Caudal ramus (Fig. 93C) as small semicircular lobe lacking caudal setae.

Rostrum absent (Fig. 93B). Antennule (Fig. 93D) as transparent lobe, unsegmented and unarmed. Antenna (Fig. 93D) small, indistinctly 2-segmented; proximal segment unarmed, but well-sclerotized; distal segment short, armed with 4 equal, simple spines.

Labrum small, slit-like, unornamented (Fig. 93B). Mandible, maxillule, and maxilla absent. Maxilliped (Fig. 93E, F) short, indistinctly segmented, tipped with small, simple, spiniform claw.

Legs 1-4 adhering closely to ventral surface of metasome, extremely flattened dorsoventrally, not observable in anterior or posterior views; endopods not discernible. Exopods armed only with spines, lacking seta, ornamented with numerous minute spinules. Leg 1 (Fig. 93G) with 5 small bifurcate spines on exopod. Leg 2 (Fig. 93H) with 1 small bifurcate spine on protopod and 4 bifurcate spines on exopod. Leg 3 (Fig. 93I) with 4 bifurcate spines on exopod. Leg 4 armed as in leg 3. Legs 5 and 6 not discernible.

Male. Unknown.

Remarks. In having 5, 4, 4, and 4 spines, respectively, on the exopods of legs 1-4, eK gracẚle sp. nov. belongs to the so-called subgroup 2 of Ooishi (1998, 2009b). However, detailed comparison with its congeners in the subgroup is unnecessary since it exhibits numerous outstanding features, including: (1) the body is extremely elongate, about 11 times longer than wide; (2) the abdomen is reduced to a small segment; (3) the caudal rami are rudimentary and lack setae; (4) the antennae and legs 1-5 are adpressed to the ventral surface of the body; (5) the mouthparts are represented only by the maxilliped; and (6) leg 5 is absent.