Didemnomolgus crenulatus, 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 : 53-56

Didemnomolgus crenulatus gen. et sp. nov.

( Figs. 33–35 )

Type material. Holotype ♀ (MNHN-IU-2014-21605) and 2 ♀♀ plus 1 ♂ dissected paratypes (MNHN-IU-2014- 21491) from aẚdemnum molle (Herdmann, 1886) MNHN-IT-2008-3125 (= MNHN A2 /DID.C/226): Open reef 1 km West of Murex Resort, West of Manado town, Sulawesi, Indonesia OCDN 1260 -F, Site Manado 3, depth 10 m, CRRF coll., 09 May 1993

Etymology. The name is derived from the Latin cren (=a notch), referring to the distally notched claw of the antenna.

Description of female. Body ( Fig. 33A ) narrow; body length 1.75 mm; prosome 1.13 mm long, with maximum width 691 μm. Cephalothorax 669 μm long, with faint dorsal suture line between cephalosome and first pedigerous somite. Second pedigerous somite with slightly extended, angular posterolateral corners. Urosome ( Fig. 33B ) 5-segmented; fifth pedigerous somite 314 μm wide, as wide as genital double-somite. Genital double-somite longer than wide (364×318 μm), with markedly expanded anterior two-thirds and narrower posterior third; genital apertures lo- cated dorsally slightly anterior to middle. Three free abdominal somites becoming shorter from anterior to posterior, 159×173, 95×152, and 68×143 μm, respectively. Caudal ramus ( Fig. 33C ) very short, about 1.7 times wider than long (30×51 μm); armed with 7 naked setae; seta I small, setule-like; setae II-VI positioned distally or subdistally.

Rostrum ( Fig. 33D ) strongly tapering; apex obscure, almost fused to ventral surface of cephalothorax. Antennule ( Fig. 33E ) slender, 409 μm long, 7-segmented; armature formula 4, 13, 6, 3, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; all setae naked. Antenna ( Fig. 33F ) 4-segmented, with armature formula 1, 1, 4, and 5+claw; all setae small, setule-like; segments narrowing gradually from proximal to distal; terminal segment ( Fig. 33G ) 3.25 times longer than wide (65×20 μm); terminal claw 42 μm long, annulated near middle, with notch at tip.

Labrum ( Fig. 33H ) with tapering posterior lobes separated by deep and broad medial incision; ornamented with transverse row of fine spinules along highly sclerotized median proximal region. Mandible ( Fig. 33I ) with elongate distal lash, 2 rows of densely arranged spinules along convex outer margin, and 1 row of spinules along inner margin. Paragnath ( Fig. 33J ) as setulose lobe. Maxillule ( Fig. 33K ) with 1 minute seta subdistally and 2 stiff setae and 1 nipple-shaped process distally. Maxilla ( Fig. 33L ) consisting of syncoxa and basis; syncoxa unarmed; basis with elongate distal lash and 2 setae (inner and anterior setae); distal lash bearing 1 large spine proximally followed by row of spinules along proximal half of outer margin; inner seta (seta I) more than half length of distal lash, with thick spinules (or denticles) along outer margin; anterior seta (seta II) small; seta III absent. Maxilliped ( Fig. 34A ) 3-segmented; first segment unarmed; second segment longest, narrowing distally, with 2 small setae; third segment with 1 minute seta proximally and tipped with 1 claw articulated from segment.

Legs 1-3 with 3-segmented rami ( Fig. 34B, C ). Outer seta on basis of leg 1-4 naked. Most of spines on rami of legs 1-3 naked, without serrations or membranous flanges. Leg 3 different from leg 2 in having 3 spines and 2 setae on third endopodal segment. Leg 4 ( Fig. 34D ) with 3-segmented exopod and 2-segmented endopod; inner coxal seta thin and naked; third exopodal segment armed with 4 spines and 5 setae; endopod small, armed with 1 inner seta on proximal segment and 1 spine and 1 seta on distal segment. Armature formula for legs 1–4 as follows:

Coxa Basis Exopod Endopod

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

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

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

Leg 4: 0-1 1-0 I-0; I-1; III, I, 5 0-1; 0, I+1, 0

Leg 5 ( Fig. 33B ) consisting of dorsolateral seta on fifth pedigerous somite and free exopod; exopodal segment ( Fig. 34E ) 1.55 times longer than wide (118×76 μm), with straight outer margin and strongly inflated inner margin bearing narrow membranous flange near apex; armed with 2 large, naked setae distally, setae more than twice as long as exopodal segment. Leg 6 represented by 2 small setae on genital operculum.

Description of male. Body ( Fig. 35A ) narrower than that of female; body length 986 μm; prosome 590×391 μm. Urosome ( Fig. 35B ) 6-segmented; fifth pedigerous somite 130 μm wide; genital somite 159×186 μm; 4 ab- dominal somites 52×93, 48×88, 25×80, and 23×77 μm, respectively. Caudal ramus about 1.8 times wider than long (18×32 μm).

Rostrum as in female. Antennule with 3 additional aesthetascs: 2 on second segment and 1 on fourth, as indicated by dots in Fig. 33E . Antenna ( Fig. 35C ) armed as in female, but all 4 setae on second endopodal segment well-developed.

Labrum, mandible, maxillule, and maxilla as in female. Maxilliped ( Fig. 35D ) 4-segmented; first segment unarmed; second segment with 2 longitudinal rows of minute spinules on inner surface, distinct projection on inner margin tipped with 1 stout, claw-like spine bearing small setule near middle, and 1 small seta near base of projection; small third segment unarmed; fourth segment as elongate claw bearing 1 minute and 1 large seta proximally.

Legs 1–4 as in female. Leg 5 exopod ( Fig. 35E ) fusiform, about 2.3 times longer than wide (64×28 μm); armed with 2 large setae distally, both setae more than twice length of exopodal segment. Leg 6 ( Fig. 35B ) represented by 2 unequal setae on genital operculum.

Remarks. The lengths of the distal setae on the free exopodal segment of leg 5 are a distinctive feature of this species: they are more than twice as long as the segment itself in both sexes.

Figures

FIGURE 33. aẚdemnomolgus crenulatus gen. et sp. nov., female. A, habitus, dorsal; B, urosome, dorsal; C, left caudal ramus, dorsal; D, rostrum; E, antennule; F, antenna; G, distal part of antenna; H, labrum; I, mandible; J, paragnath; K, maxillule; L, maxilla. Scale bars: A, B, 0.2 mm; C, G, I–L, 0.02 mm; D–F, H, 0.05 mm.

FIGURE 34. aẚdemnomolgus crenulatus gen. et sp. nov., female. A, maxilliped; B, leg 1; C, leg 2; D, leg 4; E, exopod of leg 5. All scale bars: 0.05 mm.

FIGURE 35. aẚdemnomolgus crenulatus gen. et sp. nov., male. A, habitus, dorsal; B, urosome, ventral; C, distal part of antenna; D, maxilliped; E, exopod of leg 5. Scale bars: A, 0.2 mm; B, 0.1 mm; C, D, 0.02 mm; E, 0.05 mm.