Haplostoma rectangulatum, 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 : 141

Haplostoma rectangulatum sp. nov.

( Fig. 91 )

Type material. Holotype ♀ (MNHN-IU-2009-5230) and 1 ♀ paratype (dissected, MNHN-IU-2014-17382) from mçlysyncratçn sp.; off Libanona , Sud Madagascar, ATIMO VATAE Expedition, Stn TR 01 (25°00.25´S, 46°59.4´E), depth 9 m, MNHN coll., 28 April 2010.

Additional material. 1 ♀ (MNHN-IU-2009-5232) in mçlysyncratçn sp., Port Dauphin , Madagascar, ATIMO VATAE expedition, Stn TR 03 (25°0.08´S, 47°0.01´E), depth 21 m, 29 April 2010 .

Etymology. The name of the new species refers to its rectangular abdomen.

Description of female. Body ( Fig. 91A, B ) eruciform, cylindrical, slightly curved dorsally, consisting cephalosome, indistinctly 5-segmented metasome, and small 2-segmented genitoabdomen. Body length 940 μm; maximum width 290 μm across fourth pedigerous somite. Cephalosome 175×210 μm, narrower than first pedigerous somite; second to fourth pedigerous somites nearly equal in width, each wider than first. Fourth and fifth pedigerous somites demarcated from each other by dorsal and ventral constrictions. Genitoabdomen ( Fig. 91C ) small, 105×120 μm, occupying only 11% of body length, consisting of triangular anterior somite bearing genital apertures dorsally, and narrow, rectangular free abdomen (posterior somite); free abdomen clearly defined from anterior somite due to abrupt narrowing, longer than wide (39×27 μm). Caudal rami absent, but 1 caudal seta may be present on postero- lateral corner of free abdomen ( Fig. 91D ).

Rostrum absent. Antennule ( Fig. 91E ) as small, unsegmented lobe, 24×17 μm, bearing patch of small spinules (or setae?) on apex. Antenna ( Fig. 91F ) stout, 3-segmented; first segment broad but very short and unarmed; second segment longest, unarmed; terminal segment slightly longer than wide, armed with 4 bifurcate spines; spines becoming gradually larger from proximal to distal.

Labrum ( Fig. 91G ) simple, unornamented, with broad distal lobe. Mandible ( Fig. 91G ) vestigial, represented by pair of weak unarmed tubercles, located lateral to labrum. Maxillule and maxilla absent. Maxilliped ( Fig. 91H ) stout, very small, 4-segmented; all segments wider than long; proximal 3 segments unarmed; distal segment bearing unequally bifurcate terminal claw.

Legs 1-4 consisting of protopod and exopod; endopod not discernible; exopods armed only with spines (lacking seta), incompletely articulated from protopod. Exopod of leg 1 ( Fig. 91I ) armed with 5 bifurcate spines and ornamented with spinules near base of each spine. Leg 4 ( Fig. 91J ) slightly larger than leg 1, armed with 4 bifurcate spines and ornamented as in leg 1. Legs 2 and 3 same as leg 4 in shape and armature.

Leg 5 ( Fig. 91K ) as conical fleshy process on fifth pedigerous somite, directed posterodorsally, bearing 2 small setae (1 dorsal and 1 distal). Leg 6 ( Fig. 91L ) represented by 1 small spine and 1 spiniform process on genital operculum. Four dentiform elements present near leg 6.

Male. Unknown.

Remarks. Ooishi (2009b) recognized seven species of eaplçstçma as “subgroup 2”. In one member of this group, e. bẚspẚnçsum Ooishi, 2009, the exopods of legs 1-4 are armed with 5, 4, 5, and 5 spines (5-4-5-5 pattern), respectively. The other six species of this group all display a 5-4-4-4 pattern for legs 1-4, in common with e. rectangulatum sp. nov. However, only one of these six species, e. dudleyae Ooishi, 1998, is comparable with the new species in having a single caudal seta and a vestigial mandible lacking any setal elements. Ooishi (1998) described eK dudleyae on the basis of material from Florida, USA and it has a leg 5 represented only by a pair of setae. In contrast, leg 5 of e. rectangulatum sp. nov. is well-developed, being represented by a distinct fleshy process bearing 2 setae. eaplçstçma dudleyae also has caudal rami, although they are small and lobate, while e. rectangulatum sp. nov. lacks defined caudal rami. The latter feature of the new species is unique within the genus. Collectively these differences justify the establishment of the new species.

Figures

FIG. 91. eaplçstçma rectangulatum sp. nov., female. A, habitus, dorsal; B, habitus, right; C, genitoabdomen, dorsal; D, distal part of abdomen; E, antennule; F, antenna; G, labrum and mandibles; H, maxilliped; I, leg 1; J, leg 2; K, leg 5; L, genital aperture. Scale bars: A, B, 0.1 mm; C, D, G, K, 0.02 mm; E, F, H-J, L, 0.01 mm.