Lichomolgidium sardum Kossmann, 1877

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 : 20-23

Lichomolgidium sardum Kossmann, 1877

( Figs. 12–14 )

Syn. iẚchomolgẚdẚum cynthẚae (Brian, 1924), new synonym.

Material examined. 4 ♀♀, 6 ♂♂ (MNHN-IU-2014-21596) (1 ♀ and 1 ♂ dissected) from Molgula amesophleba (Codreanu & Mack-Fira, 1956) , Etang de Leucate , Mediterranean coast of France (09°15.38´N, 124°39.12´E), coll. 1985 .

Description of female. Body ( Fig. 12A ) narrow; body length of dissected specimen 1.54 mm (other 3 specimens 1.09, 1.44, and 1.58 mm). Prosome 842 μm long; cephalothorax 491×539μm. Urosome ( Fig. 12B ) 5-seg- mented; fifth pedigerous somite 186 μm wide; genital double-somite 1.18 times longer than wide (212×179 μm), expanded in middle; genital apertures located dorsolaterally at midlength of double-somite. Three free abdominal somites 75×115, 64×96, and 85×82μm, respectively. Caudal ramus ( Fig. 12C ) about 4.9 times longer than wide (178×36 μm): armed with 6 setae; innermost distal seta (seta VI) pinnate proximally, other 5 setae naked; 2 median terminal setae tape-like, with membranous fringe along lateral margins; outer lateral seta inserted at about 65% of ramus length. Spermatophore ( Fig. 12D ) taken from female, bulbous, 84×45 μm.

Rostrum ( Fig. 12E ) narrow, longer than wide, tapering towards rounded apex. Antennule ( Fig. 12F ) 298 μm long, 7-segmented; armature formula 3, 13, 6, 3, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; all setae naked. Antenna ( Fig. 12G ) 4-segmented; armature formula 1, 1, 4, and 4+3 claws; terminal segment about 2.7 times longer than wide (75×28 μm); distal setae on terminal segment not longer than claws; one distal claw strong, other 2 claws slender, setiform, annulated in middle.

Labrum ( Fig. 12H ) deeply incised with broad, rounded posterior lobes. Mandible ( Fig. 12I ) with pair of small lobes on convex margin near base of blade; blade short and broad, lacking distal lash, with 2 rows of spinules along convex outer margin and 1 row of spinules along inner margin. Maxillule ( Fig. 12J ) armed with 1 setiform process on inner margin and 2 crossing setae on oblique distal margin. Maxilla ( Fig. 12K ) consisting of syncoxa and basis; syncoxa large but unarmed; basis with short terminal lash with broadly pectinate convex margin and bearing 2 setae (minute inner seta and longer anterior seta). Maxilliped ( Fig. 13A ) 2-segmented; proximal segment unarmed; distal segment blunt, weakly bilobed at apex, armed with 2 unequal setae on inner side, and ornamented with numerous minute spinules along outer surface.

Legs 1–4 consisting of coxa, basis, and 3-segmented rami ( Fig. 13 B-F); inner seta on coxa pinnate; outer seta on basis small, naked. Terminal process of third exopodal segment bifid in leg 1 ( Fig. 13B, C ), but trifid in legs 2–4 ( Fig. 13D, F ). Leg 3 similar to leg 2, except third endopodal segment bearing 3 spines and 2 setae ( Fig. 13E ). Articulation incomplete between second and third endopodal segments of leg 4. Third endopodal segment of leg 4 about twice as long as wide (45×23 μm), terminal 2 spines unequal, 38 μm (outer) and 88 μm (inner). 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; 0-1; 0, II, 0

Leg 5 consisting of dorsolateral seta on fifth pedigerous somite and free exopod; exopodal segment ( Fig. 13G ) 1.52 times longer than wide (73×48 μm), inflated medially, and widest at 60% of segment length; armed distally with 1 spine (33 μm long), 1 naked seta (105 μm long) and 1 minute denticle. Leg 6 ( Fig. 13H ) represented by 2 setae and 1 dentiform process, one seta stout and tipped with setule.

Description of male. Body ( Fig. 14A ) narrower than female. Body length 1.14 mm in dissected specimen; mean body length 1.12 mm (1.05-1.24 mm) based on 6 specimens; prosome 640×378 μm. Urosome ( Fig. 14B ) 6-segmented: fifth pedigerous somite 105 μm wide; genital somite subcircular, 147×141 μm; 4 abdominal somites 38×71, 42×64, 33×57, and 45×51 μm, respectively. First to third abdominal somites each fringed with spinules along posteroventral margin. Caudal ramus about 4.07 times longer than wide (110×27 μm), armed with 6 naked setae.

Rostrum as in female. Antennule with 3 additional aesthetascs, 2 on second and 1 on fourth segments, as indicated by dots in Fig. 12F . Antenna as in female.

Labrum, mandible, maxillule, maxilla as in female. Maxilliped ( Fig. 14C ) 4-segmented; first segment unarmed with inflated inner distal half; second segment with 2 setae and spinules on inner side; small third segment unarmed; fourth segment forming strongly curved, long terminal claw bearing 2 unequal setae proximally.

Legs 1-4 as in female. Exopod of leg 5 ( Fig. 14D ) about 1.8 times longer than wide (45×25 μm); outer margin distinctly convex; terminal spine 24 μm long and terminal seta 64 μm long. Leg 6 ( Fig. 14E ) represented by 2 naked setae and 1 denticle on genital operculum.

Remarks. There are three nominal species in the genus iẚchomolgẚdẚum: i. sardum from the Mediterranean, i. cynthẚae (Brian, 1924) from the Atlantic, and i. tupuhẚae Jones, 1975 from New Zealand. Our specimens taken from the ascidian Molgula amesophleba in the Mediterranean are very similar to both i. sardum and i. cynthẚae. The latter two species are very similar to each other and their known host ranges overlap, with the former recorded from myura mẚcrocosmus (Savigny, 1816) only, and the latter from m. mẚcrocosmus, Styela clava Herdman, 1881 and ealocynthẚa papẚllosa (Linnaeus, 1767) ( Gotto, 1961; Humes & Stock, 1973). Although Humes and Stock (1973) examined both Mediterranean and Atlantic material and distinguished between them, as i. sardum and i. cynthẚae, respectively, the differences they observed between the two species are very slight or unclear. We care- fully compared our specimens with the report by Humes & Stock (1973) for i. sardum and i. cynthẚae and found no meaningful difference between them, which leads us to conclude that they are all conspecific. We propose to treat i. cynthẚae (Brian, 1924) as a junior subjective synonym of iẚchomolgẚdẚum sardum Kossmann, 1877 , and our record of this species from Molgula amesophleba constitutes a new host record.

Figures

FIGURE 12. iẚchomolgẚdẚum sardum Kossmann, 1877, female. A, habitus, dorsal; B, urosome, dorsal; C, right caudal ramus, dorsal; D, spermatophore; E, rostrum; F, antennule; G, antenna; H, labrum; I, mandible; J, maxillule; K, maxilla. Scale bars: A, 0.2 mm; B, 0.1 mm; C–G, 0.05 mm; H–K, 0.02 mm.

FIGURE 13. iẚchomolgẚdẚum sardum Kossmann, 1877, female. A, maxilliped; B, leg 1; C, distal part of third exopodal segment of leg 1; D, leg 2; E, endopod of leg 3; F, leg 4; G, exopod of leg 5; H, right genital aperture, dorsal. Scale bars: A, C, G, H, 0.02 mm; B, D–F, 0.05 mm.

FIGURE 14. iẚchomolgẚdẚum sardum Kossmann, 1877, male. A, habitus, dorsal; B, urosome, ventral; C, maxilliped; D, exopod of leg 5; E, right genital operculum, ventral. Scale bars: A, 0.2 mm; B, 0.1 mm; C–E, 0.02 mm.