Lichomolgus alatus, 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 : 41-44

Lichomolgus alatus sp. nov.

( Figs. 26 , 27 )

Type material. Holotype ♀ (MNHN-IU-2014-21602, dissected and mounted on a slide) from Synoẚcum castellatum Kott, 1992 (MNHN-IT-2008-8565, = MNHN A1 /SYN/68): Reef in Channel East of Brooker I., Calvados Is. group, Louisades, Papua New Guinea, OCDN 5742-2 , site Brooker Channel, depth 7 m, CRRF coll., 01 June 1998.

Etymology. The specific name is derived from the Latin alat (=winged), referring to the wing-like posterolateral extensions of the epimera of the second pedigerous somite.

Description of female. Body ( Fig. 26A ) narrow; body length 1.34 mm long; prosome 777 μm long; maximum width 482 μm (across second pedigerous somite). Cephalothorax longer than wide (477×464 μm), with faint dorsal suture line dividing cephalosome and first pedigerous somite. Epimera of second pedigerous somite, wing-like, characteristically expanded posterolaterally. Urosome ( Fig. 26B ) 5-segmented; fifth pedigerous somite 142 μm wide; genital double-somite as long as wide (188×188 μm), widest at about 40% of double-somite length, with tapering posterior half; genital apertures positioned dorsolaterally at widest region. Three free abdominal somites longer than wide, 91×85, 88×76, and 94×89 μm, respectively; anal somite ( Fig. 26C ) ornamented with transverse rows of spinules anteriorly on ventral surface, and with minute spinules along posteroventral margin. Caudal rami ( Fig. 26C ) slightly divergent; each ramus about 3.5 times longer than wide (120×34 μm) and ornamented with minute spinules on posteroventral margin: armed with 6 setae; lateral seta naked, positioned slightly posterior to midlength of ramus; four distal setae (setae III-VI) pinnate but lateral and dorsal setae (setae II and VII) naked. Egg sac ( Fig. 27A ) cylindrical, 560×175 μm; each egg about 63 μm in diameter.

Rostrum ( Fig. 26D ) well-sclerotized, slightly longer than wide, with parallel lateral margins and rounded posterior margin. Antennule ( Fig. 26E ) 280 μm long, 7-segmented; armature formula 4, 13, 6, 3, 4+aesthetasc. 2+aes- thetasc, and 7+aesthetasc; all setae naked.Antenna ( Fig. 26F ) 4-segmented; armature formula 1, 1, 2+claw, and 3+4 claws; claw on third segment (second endopodal segment) short but strong; terminal segment about 2.1 times longer than wide (51×24 μm); four terminal claws annulated, consisting of 2 strong, shorter median claws and 2 longer, setiform claws (outer and inner).

Labrum ( Fig. 26G ) consisting of sclerotized proximal part and divergent, transparent, lamellate posterior lobes. Mandible ( Fig. 26H ) narrow, with elongate distal lash, and ornamented with row of minute spinules along convex margin and row of longer, setule-like spinules along concave margin blade and lash. Maxillule ( Fig. 26I ) with 2 unequal, naked setae apically. Maxilla ( Fig. 26J ) consisting of syncoxa and basis; syncoxa characteristically with 1 claw-like cusp at outer distal corner; basis with extremely elongate, spinulose distal lash and 2 setae; inner seta (seta I) elongate 91 μm long, with large spinules along outer margin and minute spinules along inner margin; anterior seta (seta II) small and simple; seta III absent. Maxilliped ( Fig. 26K ) 3-segmented; first segment unarmed; second segment with 2 small, unequal setae (1 vestigial); third segment claw-like, with 1 small seta proximally.

Legs 1, 2 ( Fig. 27B, C ) and 3 with 3-segmented rami. Outer seta on basis of legs 1-4 and inner coxal seta of leg 4 naked, other setae on these legs pinnate. Leg 3 same as leg 2, except third endopodal segment ( Fig. 27D ) bearing 3 spines and 2 setae. Leg 4 ( Fig. 27E ) with 3-segmented exopod and 2-segmented endopod; endopod narrow; distal endopodal segment 41×18 μm; 2 distal spines setiform 30 μm (outer) and 59 μm (inner), respectively. 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, II, 0

Leg 5 ( Fig. 27F ) consisting of dorsolateral seta on fifth pedigerous somite and free exopod; exopodal segment 1.27 times longer than wide (61×48 μm), with inflated, strongly convex inner margin and 2 long, naked setae; outer seta 117 μm and inner seta 156 μm. Leg 6 ( Fig. 27G ) represented by 2 setae and 1 blunt tubercle on genital opercu- lum.

Male. Unknown.

Remarks. About half of the known species of iẚchomolgus have a smooth outer margin on the compound distal endopodal segment of leg 4, lacking any dentiform process. Of these, only six species plus iK alatus sp. nov., have a caudal ramus that is 3 to 4 times longer than wide. These species are i. arcanus, i. asaphẚdẚs, i. canuẚ, i. furcẚllatus, i. spondylẚ, and i. trẚdacnae Humes, 1972. These six species can be distinguished from i. alatus sp. nov. by the following diagnostic features: i. canuẚ and i. furcẚllatus have 1 spine and 1 seta (rather than 2 setae, as in the new species) on the exopod of female leg 5, and i. arcanus, i. asaphẚdẚs, i. spondylẚ and i. trẚdacnae all have a single, large terminal claw on the antenna (rather than 4 claws, as in the new species).

Two key diagnostic features of i. alatus sp. nov. are the presence of wing-like, posterolaterally extended epimera on the second pedigerous somite, and the possession of a claw on the second endopodal segment of the antenna. The latter feature is unusual for iẚchomolgus, but can be observed in Zygomolgus . However, the new species is placed in iẚchomolgus because it has the typical slender mandible lacking digitiform scales on the outer side of the blade, and the proximal spinules on the distal lash of the maxilla are not specialized, compared to 3 to 5 broad, digitiform proximal spinules on the lash of Zygomolgus .

Figures

FIGURE 26. iẚchomolgus alatus sp. nov., female. A, habitus, dorsal; B, urosome, dorsal; C, anal somite and caudal rami, ventral; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule; J, maxilla; K, maxilliped. Scale bars: A, 0.2 mm; B, 0.1 mm; C, E–G, 0.05 mm; D, H–K, 0.02 mm.

FIGURE 27. iẚchomolgus alatus sp. nov., female. A, egg sac; B, leg 1; C, leg 2; D, third endopodal segment of leg 3; E, leg 4; F, leg 5; G, left genital aperture, dorsal. Scale bars: A, 0.2 mm; B–F, 0.05 mm; G, 0.02 mm.