Zygomolgus dentatus Kim I.H., 2006

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 : 70-73

Zygomolgus dentatus Kim I.H., 2006

( Figs. 43 , 44 )

Material examined. 1 ♀ (MNHN-IU-2014-21495, dissected) from a compound ascidian aẚplosoma lẚsterẚanum (Milne Edwards, 1841) MNHN-IT-2008-3533 (= MNHN A2 /DIP.A/30): Port de Sète , Mediterranean coast of France, Monniot coll., 12 March 1984 .

Supplementary description of female. Body ( Fig. 43A ) with broad prosome and narrow urosome; body length 1.67 mm; prosome 1.11 mm long, strongly tapering posteriorly. Cephalothorax markedly expanded, globular, 735×815 μm. Urosome ( Fig. 43B ) 5-segmented; fifth pedigerous somite 175 μm wide; genital double-somite as long as wide (190×190 μm), with slightly broadened anterior half; genital apertures positioned dorsolaterally at mi- dlength of double-somite. Three free abdominal somites 48×101, 38×88, and 84×95 μm, respectively; anal somite with 4 or 5 denticles each side on posteroventral margin ( Fig. 43C ). Caudal ramus ( Fig. 43C ) about 4.3 times longer than wide (156×36 μm) and 1.86 times longer than anal somite, and ornamented with 4 denticles on posteroventral margin; armed with 6 naked setae, lateral seta positioned slightly distal to midlength of ramus.

Rostrum ( Fig. 43D ) distinct, nearly semicircular. Antennule ( Fig. 43E ) 336 μm long, 7-segmented; armature formula 4, 13, 6, 3, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc (deduced from setae and their insertion scars). Antenna ( Fig. 43F ) 4-segmented, with armature formula 1, 1, 2+claw, and 3+4 claws; terminal segment about 2.6 times longer than wide (75×29 μm); claw on third segment (second endopodal segment) rather strong, annulated; four terminal claws unequal in length and thickness, outermost claw longest, slender and setiform.

Labrum ( Fig. 43G ) with broad median incision and tapering posterolateral lobes fringed with membrane; midposterior margin with row of fine spinules. Mandible ( Fig. 43H ) with elongate distal lash bearing densely arranged spinules along both margins and 3 digitiform processes (scales) on convex outer side of blade. Maxillule ( Fig. 43I ) distally with 2 broad spiniform setae, 1 shorter spiniform process, and 1 small seta. Maxilla ( Fig. 43J, K ) consisting of broad, unarmed syncoxa and basis; basis with elongate distal lash and 3 setae; distal lash with 3 thick spines proximally, followed by row of spinules on outer margin; inner seta (seta I) large, slightly shorter than distal lash, spinulose along both margins; anterior seta (seta II) simple; outer proximal seta (seta III) minute. Maxilliped ( Fig. 44A ) 3-segmented; first segment unarmed; second segment with 2 small setae and produced into claw-like process at outer distal corner (indicated by arrowhead in Fig. 44A ); small terminal segment claw-like, with 1 minute seta proximally.

Legs 1, 2 ( Fig. 44B, C ) and 3 with 3-segmented rami. Leg 4 ( Fig. 44E ) with 3-segmented exopod and 2-segmented endopod. Outer seta on basis of legs 1-4 and inner coxal seta of leg 4 small and naked, other setae pinnate. Third exopodal segment of leg 2 with bifid distal process (indicated by arrowhead in Fig. 44C ). Leg 3 same as leg 2, except third endopodal segment armed with 3 spines and 2 setae ( Fig. 44D ). Leg 4 endopod less than half length of exopod; distal endopodal segment twice as long as wide (55×24 μm), armed with 2 distal spines 35 μm (outer) and 52 μm long (inner). Armature formula for legs 1-4 as follows (same as in iẚchomolgus):

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; 0-1; I, II, 3

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

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

Leg 5 ( Fig. 43B ) consisting of dorsolateral seta on surface of somite and free exopodal segment; exopod ( Fig. 44F ) about 1.9 times longer than wide (34×18 μm), with convex outer margin, pointed inner distal corner; armed distally with 1 bilaterally serrate spine (33 μm long) and 1 naked seta (38 μm long). Leg 6 ( Fig. 44G ) represented by 2 naked setae and 1 denticle on genital operculum.

Male. Not found.

Remarks. Although the caudal ramus of our examined specimen is 4.33 times longer than wide, which differs from the 5.6 times in the type material of ZK dentatus known from Korea (Kim, I.H., 2006), our Mediterranean specimen is identified as Z. dentatus . The type material and our Mediterranean specimen share numerous specific morphological features, including the three proximal scales on the distal lash of the maxilla, the recurved, claw-like distal process on the second segment of the maxilliped, and the bifid terminal process on the third exopodal segment of leg 2, which suggest that they are conspecific. The host ascidian aẚplosoma lẚsterẚanum is a cosmopolitan species, whose known distribution includes the Atlantic, Mediterranean and North Pacific, and it is possible that ZK dentatus can be found in association with this host across its geographical range.

Gotto (1955) recorded Zygomolgus tenu ẚfurcatus as an associate of the ascidian aẚplosoma lẚsterẚanum in Northern Ireland. Although our specimen from the Mediterranean was obtained from the same ascidian host, it cannot be identified as Z. tenu ẚfurcatus, because, according to the original description ( Sars, 1917), its caudal ramus is more elongate (more than twice as long as the anal somite), and none of the above-mentioned diagnostic features of Z. dentatus is observable in his illustrations.

Figures

FIGURE 43. Zygomolgus dentatus Kim I.H., 2006, female.A, habitus, dorsal; B, urosome, dorsal; C, right caudal ramus, ventral; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule; J, maxilla; K, basis of maxilla. Scale bars: A, 0.2 mm; B, 0.1 mm; C–G, 0.05 mm; H–K, 0.02 mm.

FIGURE 44. Zygomolgus dentatus Kim I.H., 2006, female. A, maxilliped; B, leg 1; C, leg 2; D, endopod of leg 3; E, leg 4; F, exopod of leg 5; G, right genital aperture, dorsal. Scale bars: A–E, 0.05 mm; F, G, 0.02 mm.