Lichomolgus lepidotus, 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 : 44-47

Lichomolgus lepidotus sp. nov.

( Figs. 28 , 29 )

Type material. Holotype ♀ (MNHN-IU-2014-21603, dissected and mounted on a slide) from Apl ẚdẚum altarẚum (Sluiter, 1909): Mouth of Ngerduais channel, Arai, Palau (07°20.82´N, 134°34.35´E), OCDN 5002 - V, Site NGER- DWAIS3 , depth 0-5 m, CRRF coll., 09 April 1997.

Etymology. The specific name is from the Greek lepẚ (= a scale), alluding to the presence of scales on the ventral surface of the anal somite.

Description of female. Body ( Fig. 28A ) rather narrow; body length 0.96 mm; prosome 582×382 μm. Cepha- lothorax with faint dorsal suture line between cephalosome and first pedigerous somite. Urosome ( Fig. 28B ) 5-segmented; fifth pedigerous somite 118 μm wide; genital double-somite longer than wide (148×128 μm), expanded at level of genital apertures; genital apertures large, located dorsolaterally about at midlength of double-somite. Three free abdominal somites 53×68, 41×61, and 59×68 μm, respectively; anal somite ( Fig. 28C ) with 2 pairs of large, triangular membranous scales anteriorly on ventral surface and with minute spinules along posteroventral margin. Caudal ramus ( Fig. 28C ) broad, about 1.6 times longer than wide (52×32 μm) and ornamented with 3 spinules (or scales) on posteroventral margin; armed with 6 setae; outer lateral seta positioned at about 70% of ramus length; dorsal seta (seta VII) naked, other 5 setae pinnate.

Rostrum ( Fig. 28D ) evenly tapering towards rounded apex. Antennule ( Fig. 28E ) 210 μm long, 7-segmented; armature formula 4, 13, 6, 3, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; all setae naked; 1 seta on first segment much larger than other 3 setae. Antenna ( Fig. 28F ) 4-segmented; armature formula 1, 1, 3+claw, and 3+4 claws; claw on third segment small, annulated; terminal segment about 2.8 times longer than wide (50×18 μm); terminal claws consisting of 1 strong, shorter claw and 3 slender, setiform claws.

Labrum ( Fig. 28G ) with shallow median incision and broad posterior lobes bearing membranous fringe along posterior margin. Mandible ( Fig. 28H ) slender, with elongate distal lash and row of spinules along both margins of blade and lash. Maxillule ( Fig. 28I ) with 3 unequal setae apically. Maxilla ( Fig. 28J ) consisting of syncoxa and basis; syncoxa unarmed; basis with extremely elongate distal lash and 2 setae on basis; larger inner seta 84 μm long, spinulose along outer margin; anterior seta naked and slender; proximal seta (seta III) absent. Maxilliped ( Fig. 28K ) 3-segmented; first segment unarmed; second segment with 1 seta and 1 insertion scar of seta; third segment attenuated, claw-like, with 1 small seta proximally.

Legs 1-3 ( Fig. 29 A-C) with 3-segmented rami. First and second endopodal segments of legs 1-3 produced into well-developed outer distal process. Inner coxal seta of leg 4 small and naked. Outer seta on basis of legs 1-4 naked. Leg 4 ( Fig. 29D ) with 3-segmented exopod and 2-segmented endopod; endopod ( Fig. 29E ) slender, second segment 36×10 μm, with 2 terminal spines 19 μm (outer) and 43 μm long (inner). Armature formula for legs 1-4 as in i. alatus sp. nov.

Leg 5 ( Fig. 28B ) consisting of dorsolateral seta on fifth pedigerous somite and free exopod; exopodal segment ( Fig. 29F ) about 1.6 times longer than wide (55×34 μm), tapering, with inner proximal swelling: armed distally with 2 extremely unequal setae; inner seta 196 μm long, extending beyond posterior margin of genital double-somite, about 3.5 times longer than outer seta. Leg 6 ( Fig. 29G ) represented by 2 setae and 1 denticle on genital operculum.

Male. Unknown.

Remarks. Most species of iẚchomolgus have elongate caudal rami. However in four species the caudal ramus is relatively short as in i. lepẚdotus sp. nov., with a length/width ratio more than 1:1 but less than 2:1. These four species are i. fusẚformẚs, i. nakaẚẚ, i. pectẚnatus, and iK brevẚcaudatus sp. nov. described above. All four of these species have a dentiform process on the outer margin of the compound distal endopodal segment of leg 4, and therefore can easily be differentiated from the new species. As additional differences, i. fusẚformẚs, i. nakaẚẚ, and i. pectẚnatus all have 1 spine and 1 seta on the exopod of leg 5 (in contrast to 2 setae in i. lepẚdotus sp. nov.), and i. brevẚcaudatus sp. nov. has 3 claws on the terminal segment of the antenna (cf. 4 claws in i. lepẚdotus sp. nov.).

Two diagnostic features allow i. lepẚdotus sp. nov. to be easily distinguished from its congeners. One of these, the possession of 1 claw and 3 setae on the third segment (the second endopodal segment) of the antenna, is unique within the genus. The other diagnostic feature is having the two distal setae on the exopod of leg 5 extremely unequal. In about half of iẚchomolgus species the exopod of leg 5 is armed with two setae (the remaining half are armed with 1 spine and 1 seta) and the longer seta is at most about twice the length of the shorter seta. The possession of an enlarged inner seta on the exopod of leg 5 (about 3.5 times longer than the outer seta), is another unique feature of i. lepẚdotus sp. nov.

Figures

FIGURE 28. iẚchomolgus lepẚdotus 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, B, 0.1 mm; C, D, F, H–K, 0.02 mm; E, G, 0.05 mm.

FIGURE 29. iẚchomolgus lepẚdotus 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. Scale bars: A–D, 0.05 mm; E–G, 0.02 mm.