Haplostoma depressum, 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 : 155-158

Haplostoma depressum sp. nov.

( Figs. 100 , 101 )

Type material. Holotype ♀ (MNHN-IU-2009-5190), 4 ♀♀ paratypes (MNHN-IU-2014-21515), and 2 ♀♀ para- types (dissected, MNHN-IU-2014-17385) from Aplẚdẚçpsẚs pyrẚfçrmẚs (Herdman, 1886); Kerguelen, MD42 - SIBEX cruise, RV “Marion Dufresne”, Stn 4/CP25 (53°11’S, 74°05’E), depth 285-375 m, MNHN coll., 14 January 1985.

Additional material. 4 ♀♀ (MNHN-IU-2014-21516) from Aplẚdẚum fuegẚense Cunningham, 1871; Kerguelen, no other locality data; 7 ♀♀ in A. pyrẚfçrmẚs, SSE Kerguelen Is., MD04 -BENTHOS cruise, R. V. “Marion Dufresne”, Stn DC 275 (49°58’S, 70°29’E), depth 234 m, Boury-Esnault coll., 15 March 1975 .

Etymology. The body of the new species is dorsoventrally depressed, hence its name.

Description of female. Body ( Fig. 100 A-C) eruciform, slightly depressed dorsoventrally, consisting of cephalosome, 4-segmented metasome, and small genitoabdomen. Body length 1.91 mm in dissected specimen ( Fig. 100B ); maximum width 740 μm across last metasomite and maximum dorsoventral depth 542 μm. Cephalosome distinctly narrower than metasome, metasome gradually broadening posteriorly, obscurely segmented in dorsal and ventral views ( Fig. 100A, B ), but metasomites distinctly defined by dorsal and ventral constrictions ( Fig. 100C ). Compound last metasomite consisting of fused fourth and fifth pedigerous somites. Genitoabdomen ( Fig. 100D ) as long as wide (262×258 μm), 2-segmented; anterior somite subcircular, with traces of 2 suture lines on dorsal sur- face; small posterior somite (free abdomen) distinctly defined from anterior somite, wider than long in contracted specimen ( Fig. 100D ), but longer than wide in relaxed specimen ( Fig. 100E ). Caudal ramus ( Fig. 100F ) strongly tapering, armed with 2 setae (1 dorsal and 1 on outer margin) and 2 distal spines. Distal spines (ventral and dorsal) on caudal ramus unequal; ventral spine smaller and simple; larger dorsal spine bifurcate, with pointed dorsal and blunt ventral branches; ventral branch invariably ornamented with 1 or 2 minute spinules subdistally.

Rostrum as small, semicircular anterior protuberance on cephalosome. Antennule ( Fig. 100G ) 3-segmented; articulation incomplete between 2 distal segments; armed with 2, 2, and 13 small setae on first to third segments, respectively; one seta on second segment consisting of extremely swollen proximal half and slender distal half. Antenna ( Fig. 100H ) 2-segmented; proximal segment unarmed; distal segment 2.6 times longer than wide (43×16 μm), as long as proximal, armed with 4 simple spines, proximal 2 smaller than distal 2; all spines distinctly articulated at base.

Labrum ( Fig. 100I ) bearing 4 broad lobes on posterior margin, lateral lobes longer, prominent, medial lobes short. Labium well-developed, located posterior to labrum. Mandible ( Fig. 100J ) distinctly 2-segmented; tapering proximal segment unarmed; distal segment 1.8 times longer than wide, tipped with 2 equal setae. Maxillule and maxilla absent. Maxilliped ( Fig. 101A ) 4-segmented; broad first segment unarmed; second segment also wider than long, bearing 2 leaf-like setae; short third segment unarmed; fourth segment with 1 small seta distally; terminal claw unequally bifurcate.

Legs 1-4 each consisting of protopod, exopod, and endopod; protopods lacking outer seta. Exopods incompletely articulated from protopods. Endopods prominent, semicircular, indistinctly defined from protopods. Exopod of leg 1 ( Fig. 101B ) armed with 1 seta and 4 simple spines, proximal 2 spines smaller than distal 2. Exopod of leg 2 ( Fig. 101C ) armed with 1 seta and 3 simple spines; spines becoming larger from proximal to distal. Exopod of leg 3 ( Fig. 101D ) armed with 1 seta and 2 simples spines. Leg 4 shaped and armed as leg 3.

Leg 5 ( Fig. 101E ) short, wider than long, strongly tapering towards blunt apex; armed with 1 subdistal and 2 distal, small setae. Leg 6 ( Fig. 101F ) 1 small spine, 2 unequal, spiniform processes, and 1 small setule on genital operculum; 5 internal dentiform elements present near leg 6.

Male. Unknown.

Remarks. The combination of armature elements on the exopods of legs 1-4 of e. depressum sp. nov. is 5, 4, 3, and 3, as in e. albẚcatum, e. dentatum Ooishi & Illg, 1977, e. elegans Ooishi & Illg, 1977, e. mẚnutum, and e. eruca. eaplçstçma depressum sp. nov. can be clearly distinguished from those five species as well as all other congeners by the three following features: (1) the caudal ramus is armed with 2 spines and 2 setae; (2) the labrum bears 4 lobes on the posterior margin; and (3) the mandible is 2-segmented. Although the second feature is shared with e.

ambẚguum, the 4 lobes on the labrum of the latter species are equally weak, unlike the combination of 2 large lateral and 2 weak medial lobes in the new species.

Figures

FIG. 100. eaplçstçma depressum sp. nov., female. A, B, habitus, dorsal; C, habitus, left; D, genitoabdomen, dorsal; E, abdomen, dorsal; F, right caudal ramus, medial; G, antennule; H, antenna; I, labrum, mandibles, and labium; J, mandible. Scale bars: A-C, 0.2 mm; D, E, 0.05 mm; F-J, 0.02 mm

FIG. 101. eaplçstçma depressum sp. nov., female. A, maxilliped; B, leg 1; C, leg 2; D, leg 3; E, leg 5; F, genital aperture. Scale bars: A-D, F, 0.02 mm; E, 0.05 mm.