Haplostoma simplex, 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 : 164-166

Haplostoma simplex sp. nov.

( Figs. 107 , 108 )

Type material. Holotype ♀ (intact, MNHN-IU-2014-21521) from Cẚtçrclẚnum labçuteẚ Monniot F. & Millar, 1988; New Caledonia, UA281 , depth 33 m, August 1986.

Etymology. The name is derived from the Latin sẚmpl (=simple), referring to the simplified armature of legs and the loss oral appendages.

Description of female. Body ( Fig. 107 A-C) maggot-shaped, slightly dorsoventrally depressed; body length 1.18 mm, maximum width 427 μm (across second metasomite). Cephalosome ( Fig. 107D ) indistinctly defined from metasome, narrower than metasome; 4 metasomites defined by weak constrictions. Last metasomite bearing 3 broad lobes along posterodorsal margin. Genitoabdomen ( Fig. 107E ) small, unsegmented, occupying only about 8% of body length, obscurely defined from metasome; genital apertures not seen, probably concealed by posterodorsal lobes of last metasomite. Caudal rami ( Fig. 107F ) small, 1.23 times longer than wide (27×22 μm), rounded distally, originating on ventral surface of genitoabdomen; armed with 2 small setae (1 outer and 1 distal).

Rostrum ( Fig. 107D ) small, wider than long, with convex posterior margin. Antennule ( Fig. 107G ) unsegmented, with partial suture line subdistally, armed with 8 small, blunt setae. Antenna ( Fig. 107H ) 2-segmented; proximal segment plate-like, broad, short, and unarmed; distal segment with 2 spines (trifurcate distal and bifurcate subdistal), 1 rudimentary seta at distal third, and 1 row of minute spinules near middle.

Labrum ( Fig. 107D, I ) small, slit-like, unornamented. Mandible, maxillule, and maxilla absent. Maxilliped ( Fig. 108A ) consisting of 4 segments plus terminal claw; all segments unarmed and unornamented; first segment platelike, much broader than other segments; terminal claw short, curved.

Leg 1 ( Fig. 108B ) consisting of protopod and exopod. Protopod lacking outer seta. Exopod tapering, not articulated from protopod, armed with 1 small seta on outer margin and 1 spine distally; distal spine ( Fig. 108C ) bifurcate, with ventral and dorsal branches, bearing 1 small setule in middle of outer surface. Endopod not defined. Legs 2-4 same as leg 1 in form and armature. Legs 5 and 6 not seen.

Male. Unknown.

Remarks. eaplçstçma sẚmplex sp. nov. may readily be distinguished from its congeners by the armature of legs 1-4. All of the legs are identical: each has 1 outer seta and 1 distal, bifurcate spine on the exopod. Across all species of eaplçstçma this is the smallest known number of armature elements on the legs; for example, all other species are known to have at least 4 armature elements on the exopod of leg 1. The distal spine of the exopod of each leg is specialized; it is bifurcate with dorsal and ventral branches (not inner and outer branches as is typical) and it bears a setule on its outer surface.

eaplçstçma sẚmplex sp. nov. exhibits several other unusual features, including the lack of the mandible and leg 5, the possession of small caudal rami bearing only 2 simple setae, and the presence of 2 spines and 1 rudimentary seta on the antenna.

Figures

FIG. 107. eaplçstçma sẚmplex sp. nov., female.A, habitus, dorsal; B, habitus, left; C, habitus, ventral; D, cephalosome, ventral; E, genitoabdomen, dorsal; F, right caudal ramus, ventral; G, antennule; H, antenna, distal; I, labrum. Scale bars: A-C, 0.2 mm; D, E, 0.05 mm; F, G, I, 0.02 mm; H, 0.01 mm.

FIG. 108. eaplçstçma sẚmplex sp. nov., female. A, maxilliped; B, leg 1; C, distal part of exopod of leg 1, outer.