Critomolgus nudus, Kim, 2000

Kim, Il-Hoi, 2000, Poecilostomatoid Copepods from an Intertidal Mud Flat in the Yellow Sea, Journal of Natural History 34 (3), pp. 367-432 : 423-428

Critomolgus nudus n. sp.

( Figures 35 ±37)

Material examined. Seven mm, 13 ll from the pennatulacean, V irgularia gustaviana (Herklots), dug from the intertidal mud ¯at at Jakyak-do Island , on 13 December 1996. Holotype (m) allotype and 14 paratypes (four mm, ten ll) have been deposited in the US National Museum of Natural History, Smithsonian Institution. Dissected specimens (two mm, two ll) are kept in the collection of the author.

Female. Body (®gure 35A) 2.00 mm long. Greatest width 1.00 mm. Prosome ovoid, broad and dorsoventrally ¯at, with weak suture line between cephalosome and ®rst pedigerous somite. Urosome ®ve-segmented, with thick exoskeleton. Fifth pedigerous somite 290 mm wide. Genital double-somite 293Ö 305 mm, with greatest dorsal. Scales: A = 0.05 mm; B±G = 0.1 mm.

width across anterior third and weak lobate process just posterior to genital area. Genital area located dorsolaterally. Three abdominal somites 115Ö180, 85 Ö163, and 110Ö 162 mm, respectively. First two abdominal somites each broadened posteriorly. Caudal ramus short, 77Ö 64 mm (1.20:1), with six setae. Outer lateral seta naked, located in the middle of, and about twice as long as, caudal ramus. Inner dorsal seta naked. Other four setae plumose.

Rostrum weakly developed, its posterior margin obscure (®gure 36B). Antennule slender, 592 mm long, with armature formula 4, 13, 6, 3, 4 +1 aesthetasc, 2 +1 aesthetasc, and 7 +1 aesthetasc. Setae relatively short. Antenna (®gure 35D) stocky, with armature formula 1, 1, 2 +1 claw, 5 +2 claws. Setae on ®rst two segments small. Terminal segment about twice as long as wide; two of setae near outer distal corner short and broad. Two terminal claws strong.

Labrum (®gure 35F) deeply incised; lateral margins nearly parallel; posterior margin unornamented. Mandible (®gure 35G) with deep proximal notch; terminal lash narrow, spinulated and moderately long; inner margin perpendicular to lash, with row of ®ne spinules; convex side broadly produced, with row of spinules and one small, dentiform process. Paragnath (®gure 35H) a lobe, distally hairy. Maxillule (®gure 35I) with one lateral seta (or process) and three broad terminal setae. Maxilla (®gure 35J) two-segmented; ®rst segment with minute spinules on outer (ventral) surface; second segment with one minute outer seta, one long, curved seta (spinulated on inner margin) on inner margin, one small seta on anterior surface, and one small denticle near base of lash; lash shorter than seta on inner margin, with serrate convex margin. Maxilliped (®gure 36A) three-segmented and stocky; ®rst segment unarmed; second segment with two simple setae of unequal length; third segment terminating in a blunt process, with one spine and one small seta.

Leg 1 (®gure 36C), leg 2 (®gure 36D) and leg 3 with three-segmented rami. Leg 4 (®gure 36F) with three-segmented exopod and two-segmented endopod; inner seta on coxa small and naked; both terminal corners of second endopodal segment with pointed process; terminal spines unequal in length. Armature formula of legs 1±4 as follows:

Leg 5 consisting of one naked seta on ®fth pedigerous somite and free segment (®gure 36G). Free segment 109Ö 38 mm (2.87:1), with convex inner margin and two subequal, naked setae; these two setae longer than free segment. Leg 6 represented by two spinules and one spinule-like process in genital area.

Male. Body (®gure 37A) resembling that of female. Length 1.80 mm. Greatest width 0.80 mm. Urosome (®gure 37B) six-segmented. Fifth pedigerous somite short, 230 mm wide. Genital somite nearly spherical, large, 370Ö 450 mm. Four abdominal somites 75 Ö138, 70 Ö130, 50 Ö120, 70 Ö 132 mm, respectively. Caudal ramus 60 Ö 52 mm (1.15:1).

Antennule with three additional aesthetascs: two on second and one on fourth segments (opposite places of dark dots in ®gure 35C). Antenna as in female.

Maxilliped (®gure 37C) consisting of three segments and claw. First segment unarmed and similar in length to second segment. Second segment with one row of spinules on inner side, and two equal, small setae at midlength of inner margin. Third segment unarmed. Claw strongly curved, proximally with one small and one thick seta.

Terminal endopodal segment of leg 1 with two terminal processes more prominent than in female, but armature formula of legs 1± 4 as in female. Free segment of leg 5 rather varied in shape (®gure 37E, F), 55Ö 23 mm (2.39:1). Leg 6 represented by two small setae on genital ¯ap.

Etymology. The speci®c name is derived from the Latin nudus , meaning`naked’, and alludes to the relatively smooth appearance of the body, especially the naked terminal setae on the caudal rami.

Remarks. Since Humes and Boxshall (1996) counted 27 species in Critomolgus, Kim (1996) added three new species to this genus from Korean sea anemones. According to Humes (1978) the ornamentation on the ®rst segment of the maxilla is found only in C. virgulariae ( Humes, 1978) and C. magni ®cus (Humes, 1964). For this point, C. nudus n. sp. is comparable with these two species. In addition, these two species and C. nudus have in common more important characters, such as lacking sexual dimorphism on the third endopodal segment of leg 1, i.e. one spine and ®ve setae (I, 5) in both sexes. Moreover, they are all found on pennatulaceans in the Indo-West Paci®c region.

The easiest way to di erentiate the new species from the above mentioned two congeners can be made by their sizes; while the female of C. magni ®cus is unusually large, 3.06 mm long (Humes, 1964), that of C. virgulariae is relatively small, 1.12 mm long ( Humes, 1978), and the new species is intermediate, being 2.00 mm. More precise di erentiation of the females of these species may be summarized as follows:

Critomolgus nudus : genital double-somite slightly wider than long; caudal ramus 1.20 times as long as wide; maxillule bearing four setae; and free segment of leg 5 2.87 times as long as wide.

Critomolgus magni ®cus: genital double-somite 1.55 times as long as wide; caudal ramus very long (ratio of length to width 7.8); maxillule with three setae; and free segment of leg 5 2.87 times as long as wide.

Critomolgus virgulariae : genital double-somite 1.34 times wider than long; caudal ramus 1.67 times as long as wide; maxillule with three setae; and free segment of leg 5 4.33 times as long as wide.

Figures

FIG. 35. Critomolgus nudus n. sp., female: (A) habitus, dorsal; (B) urosome, dorsal; (C) antennule; (D) antenna; (E) distal part of terminal segment of antenna; (F) labrum; (G) mandible; (H) paragnath; (I) maxillule; (J) maxilla. Scales: A = 0.5 mm; B±D = 0.1 mm; E, H, I =0.02 mm; F, G, J =0.05 mm.