Spheromolgus rarus, Kim & Boxshall, 2021

Kim, Il-Hoi & Boxshall, Geoff A., 2021, Copepods associated with Ascidian hosts (Tunicata): Intramolgidae and Lichomolgidae, with descriptions of four new genera and 13 new species, Zootaxa 5013 (1), pp. 1-75 : 57-60

Spheromolgus rarus gen. et sp. nov.

( Figs. 36 , 37 )

Type material. Holotype ♀ (MNHN-IU-2014-21606, dissected and mounted on a slide) from aẚplosoma sẚmẚle (Sluiter, 1909): Iles Mescha, Djibouti, intertidal, Monniot coll., October 1996

Additional non-type material. 1 ♀ (MNHN-IU-2014-21492, dissected) in aK sẚmẚle (MNHN-IT-2008-3609 = MNHN A2 /DIP.A/55), Canal Woodin , Grande Terre, New Caledonia, Stn NC 23, depth 3 m, Monniot coll., 18 September 1985 .

Etymology. The name is derived from the Latin rar (=rare), alluding to the discovery of only single specimens of the new species at each of the two localities.

Description of female. Body ( Fig. 36A ) broad; body length 1.01 mm; prosome 690×536 μm, occupying 68% of body length. Cephalothorax spherical, 490 μm long. Urosome ( Fig. 36B ) stocky, 5-segmented; fifth pedigerous somite 120 μm wide; genital double-somite wider than long (140×153 μm), widest at about 70% of length of dou- ble-somite; genital apertures large, located dorsolaterally at widest region. Three free abdominal somites 25×71, 20×66, and 45×71 μm, respectively; anal somite with large anal region and row of spinules along posteroventral margin ( Fig. 36C ). Caudal ramus ( Fig. 36C ) broad, about 1.5 times longer than wide (46×30 μm), and ornamented with row of spinules along posteroventral margin; armed with 6 naked setae, lateral seta (seta II) positioned at 65% of ramus length.

Rostrum ( Fig. 36D ) broad, semicircular. Antennule ( Fig. 36E ) 218 μm long, 7-segmented; first segment broad- ened; armature formula 4, 13, 6, 3, 4+aesthetasc. 2+aesthetasc, and 7+aesthetasc; all setae naked. Antenna ( Fig. 36F ) 4-segmented, with armature formula 1, 1, 4, and 3+3 claws; terminal segment about 2.2 times longer than wide (59×27 μm); 3 terminal claws annulated, unequal in length and thickness, 64, 31, 18 μm long, respectively; 1 seta on each of third and terminal segments minute, setule-like.

Labrum ( Fig. 36G ) with relatively small posterolateral lobes, separated by broad, shallow median incision; with transverse row of minute spinules at mid-posterior region. Mandible ( Fig. 36H ) blade slightly broadened with spinulose inner margin perpendicular to distal lash; lash rather short bearing 2 rows of denticles along convex outer margin and few minute spinules on inner margin. Maxillule ( Fig. 36I ) with 1 minute subdistal and 2 distal setae. Maxilla ( Fig. 36J ) consisting of syncoxa and basis; syncoxa broad, unarmed; basis terminating in recurved distal lash and 2 setae (setae I and II); distal lash thin, elongate, with row of long spinules along outer margin and several, shorter spinules on proximal part of inner margin; inner seta (seta I) spiniform, ornamented with broad spinules along outer margin and small spinules along inner margin; anterior seta (seta II) abruptly narrowed from middle, with thin, needle-like distal half. Maxilliped ( Fig. 36K ) 3-segmented; fist segment unarmed; second segment with protruding, convex inner margin bearing 1 blunt tubercle proximally plus 2 small setae; terminal segment claw-like, narrowing distally, with 2 small setae proximally, and ornamented with row of about 5 spinules in distal half.

Legs 1, 2 ( Fig. 37A, B ) and 3 with 3-segmented rami. Leg 3 same as leg 2 except third endopodal segment bearing 3 spines and 2 setae ( Fig. 37C ). Leg 4 ( Fig. 37D ) with 3-segmented exopod and 2-segmented endopod. Inner coxal seta of legs 1-3 well-developed, pinnate, that of leg 4 small and naked. Outer seta on basis sparsely pinnate in legs 1 and 4, but naked in legs 2 and 3. Leg 4 endopod small, less than half length of exopod; second endopodal segment of left leg 4 bearing small dentiform process at inner distal corner ( Fig. 37D ), but same segment of right leg 4 bearing large distal process at outer distal corner ( Fig. 37E ); terminal spine on distal endopodal segment naked, as long as distal segment. Armature formula for legs 1–4 as follows:

Coxa Basis Exopod Endopod

Leg 1: 0-1 1-0 I-0; I-1; III, I, 4 0-1; 0-1; I, 1, 4

Leg 2: 0-1 1-0 I-0; I-1; III, I, 5 0-1; 0-2; I, II, 3

Leg 3: 0-1 1-0 I-0; I-1; III, I, 5 0-1; 0-2; I, II, 2

Leg 4: 0-1 1-0 I-0; I-1; II, I, 5 0-1; 0, I, 0

Leg 5 consisting of dorsolateral seta on fifth pedigerous somite and free exopodal segment ( Fig. 37F ) 1.45 times longer than wide (29×20 μm), narrowing distally, with convex outer margin; distally with 1 dentiform process, 1 spine (24 μm long) and 1 naked seta (26 μm long). Leg 6 ( Fig. 37G ) represented by 2 setae and 2 denticles on genital operculum.

Male. Unknown.

Remarks. The asymmetry of leg 4 is unusual: in the left leg the second endopodal segment bears a small dentiform process at the inner distal corner whereas on the right leg this segment has a large process at the outer distal corner. The figured specimen may simply be aberrant but more material will be needed to confirm this.

Figures

FIGURE 36. Spheromolgus rarus gen. et sp. nov., female. A, habitus, dorsal; B, urosome, dorsal; C, caudal rami, ventral; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule; J, maxilla; K, maxilliped. Scale bars: A, B, 0.1 mm; C, E–K, 0.02 mm; D, 0.05 mm.

FIGURE 37. Spheromolgus rarus gen. et sp. nov., female. A, leg 1; B, leg 2; C, endopod of leg 3; D, leg 4; E, endopod of leg 4; F, exopod of leg 5; G, right genital aperture, dorsal. All scale bars: 0.02 mm.