Haplostoma pygmaeum, 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 : 166-169

Haplostoma pygmaeum sp. nov.

( Fig. 109 )

Type material. Holotype ♀ (MNHN-IU-2014-21522, dissected and mounted on a slide) from Cystçdytes dellechẚaje ẚ (Della Valle, 1877); New Caledonia, Récif Neobumki, 1 mile North of passe de Kouaré, Stn NC 31, depth 10- 40m, Monniot coll., 10 March 1987.

Etymology. The name is derived from the Greek pygm (=a fist), alluding to the fist-like distal armature on exopods of legs 1-4.

Description of female. Body ( Fig. 109A, B ) eruciform, robust, dorsoventrally depressed, divisible into cephalosome, 4-segmented metasome, and 2-segmented genitoabdomen. Body length 1.10 mm; maximum width 512 μm (across third metasomite). Cephalosome 231×296 μm, clearly defined from and distinctly narrower than first meta- somite; metasome gradually broadening posteriorly; 4 metasomites well-defined from one another. Genitoabdomen ( Fig. 109C ) 172×183 μm; genital apertures large, positioned dorsolaterally. Abdomen strongly tapering, 1.9 times wider than long. Caudal rami convergent, small; each ramus ( Fig. 109D ) wider than long (25×28 μm), armed with 6 setae (2 rudimentary, papilliform).

Rostrum absent. Antennule ( Fig. 109E ) 2-segmented, 76 μm long; broad proximal segment with 2 setae; nar- rower distal segment less than half length of proximal segment, armed with 12 setae and 1 aesthetasc.Antenna ( Fig. 109F ) 2-segmented; proximal segment unarmed; distal segment as long as proximal segment, about 2.6 times longer than wide (37×14 μm); armed with 4 spines (proximal 2 small and transparent, distal 2 broad, with serrate distal margin).

Labrum ( Fig. 109G ) with convex posterior margin bearing thin, transparent fringe. Mandible ( Fig. 109H ) as elongate lobe tipped with 1 small seta. Maxillule and maxilla absent. Maxilliped ( Fig. 109I ) robust, 4-segmented; first segment broad but unarmed; second segment much wider than long, with 1 small, blunt seta mediodistally; third and fourth segments small, unarmed; terminal claw small and simple.

Leg 1 ( Fig. 109J ) consisting of protopod and exopod, but lacking articulation: protopod unarmed; endopod absent. Exopod digitiform, armed distally with subglobular, fist-like element articulated from exopodal segment at base, and bearing 1 small, claw-like process on outer margin and ornamented with about 10 spinules (or denticles) on anterior surface; no seta or spine present on exopod. Legs 2-4 as leg 1 in shape and armature.

Leg 5 ( Fig. 109K ) located on posteroventral surface of last metasomite; present as small knob tipped with 1 broad, blunt seta and 1 thin, longer seta. Leg 6 ( Fig. 109L ) represented by 1 small spine and 2 spiniform processes on genital operculum; 5 minute denticles present posterior to leg 6, and row of 5 spinules present lateral to leg 6.

Male. Unknown.

Remarks. The taxonomic position of eaplçstçma pygmaeum sp. nov. seems to lie close to the boundary between eaplçstçma and the related genus eaplçsaccus Chatton & Harant, 1924. In the original description of eaplçsaccus given by Chatton & Harant (1924c), three characters were highlighted as diagnostic features for the new genus: (1) the caudal rami are extremely reduced; (2) the antenna is armed with a strong distal claw; and (3) the exopods of legs 1-4 have a terminal hook. In retaining distinct caudal rami and in the presence of 4 spines on the last segment of the antenna, the new species seems better placed in eaplçstçma. The peculiar form of the exopod of legs 1-4, which bears only the fist-like terminal element, is a distinctive autapomorphy of e. pygmaeum sp. nov. We infer that this exopod is derived from the single spine-bearing type of exopod, as found in eaplçstçma.

Genus Haplosaccus Chatton & Harant, 1924

Diagnosis (female). Body eruciform or vermiform, unsegmented. Genitoabdomen defined by its narrowness; genital apertures positioned dorsolaterally, with copulatory pore on ventral surface. Caudal rami vestigial. Rostrum present or absent. Antennule short, at most 2-segmented, armed with setae. Antenna 2- or 3-segmented; terminal segment armed distally with 1 claw only, or 1 claw plus 1 spine, or 2 spines. Labrum present. Mandible absent, or represented by 1 seta or as digitiform, distally bilobed process. Maxillule and maxilla absent. Maxilliped consisting of 4 segments plus terminal claw. Legs 1-4 same in form and armature, consisting of unarmed protopod plus rami; exopod distally with 1 strong claw or bifurcate spine, with or without 1 seta on outer margin; endopod variably defined. Leg 5 represented by 1 small seta or absent. Leg 6 represented by 1 spine and 1 spiniform process on genital operculum, accompanied with 5 dentiform elements.

Type species. eaplçsaccus sacculus ( Chatton & Brément, 1910) (originally as Aplçstçma sacculus) by original designation.

Remarks. The discovery of eaplçsaccus ardẚus sp. nov. described below, raises uncertainty about the generic position of e. elçngatus Ooishi & Illg, 1977. The most important diagnostic features of eaplçsaccus seem to be the presence of a strong terminal claw on the antenna and on each of the exopods of legs 1-4. The type species e. sacculus and e. ardẚus sp. nov. share these features, but e. elçngatus does not. It seems possible that eK elçngatus should be transferred to another genus, possibly eaplçstçma, but this must await re-examination of the type material. The major morphological differences between these three species, their known hosts and their distributions are given in Table 5 .

Figures

FIG. 109. eaplçstçma pygmaeum sp. nov., female. A, habitus, dorsal; B, habitus, ventral; C, genitoabdomen, dorsal; D, right caudal ramus, dorsal; E, antennule; F, antenna; G, labrum; H, mandible; I, maxilliped; J, leg 1; K, leg 5; L, genital aperture. Scale bars: A, B, 0.1 mm; C, 0.05 mm; D-G, I-L, 0.02 mm; H, 0.01 mm.