Indoclausia bipartita Kim 2014, n. sp.

Indoclausia bipartita n. sp. (Figs. 1-3)

Material examined. 9 from washings of several species of polychaetes epizoic on shells of the oyster Ostrea denselamellosa Lischke, bought at a fish market at Daecheon (36 19′44′′N, 126 30′18′′E) on the coast of the Yellow Sea, 15 August 2004. Holotype (NIBRIV0000286624), allotype (, NIBRIV0000286625), and paratypes (6, 9, NIBRIV0000286626) have been deposited in the National Institute of Biological Resources (NIBR), Incheon, Korea. Dissected paratypes (2

Female. Body (Fig. 1A) elongate and cylindrical. Mean body length 2.87 mm (2.48-3.47 mm) based on 8 specimens. Dissected specimen 3.30 mm long. Prosome-urosome division indistinct. Prosome longer than urosome, unsegmented, but each somite clearly defined by constrictions between somites. Cephalothorax nearly circular, 653 693 Μm, with slightly produced and truncated anterior apex. Second to fourth pedigerous somites 346 673, 426 574, and 495 564 Μm, respectively, with rounded lateral margins. Urosome (Fig. 1B) 4-segmented, consisting of fifth pedigerous somite, genital double-somite, and 2 free abdominal somites. Fifth pedigerous somite about 465 594 Μm and nearly hexagonal. Genital double-somite 238 520 Μm, much wider than long; genital aperture located dorsally. Two free abdominal somites 158 350 and 218 304 Μm, respectively. Anal somite (second free abdominal somite) distinctly longer than first free abdominal somite, without ornamentation on ventral surface. Caudal rami parallel and widely separated from each other; each ramus gradually narrowing distally, 264 105 Μm (ratio 2.51: 1), with 6 naked setae; outer lateral seta locating at midlength of ramus; largest terminal seta (seta V) 541 Μm long; next largest seta (seta IV) 198 Μm long; other 4 setae much smaller, shorter than ramus width.

[table omitted]

Rostrum distinct, highly sclerotized and much broader than long, with convex posterior margin (Fig. 2A). Antennule (Fig. 1C) 383 Μm long and 6-segmented, with armature formula 5 (or 6), 18, 14, 4, 2+aesthetasc, and 7+ aesthetasc; first segment short but widest among segments; remaining segments gradually narrowing; suture between second and third segments indistinct; setae dense on second and third segments; all setae naked and thin. Antenna (Fig. 1D) 3-segmented; first segment (basis) longer and wider than 2 distal segments, with 1 seta medio-distally; second segment (first endopodal segment) unarmed but ornamented with large patch of fine spinules on medio-distal surface; terminal segment (second endopodal segment) shorter than second segment and armed with 4 distal claws of unequal sizes, 2 outer subdistal setae, 2 medial subdistal claws, and 1 minute medial seta proximal to 2 subdistal claws (Fig. 1E) and ornamented with 2 patches of fine spinules, one of latters on medial surface and the other on posterior surface (latter not figured in Fig. 1D, E).

Labrum unornamented, with deep and broad posteromedian invagination (Fig. 2A). Mandible (Fig. 1F) elongate, with 2 unequal distal elements: larger element 49 Μm long, with 6 or 7 teeth in distal region; smaller element as flame-shaped broad seta. Paragnath not discernible. Maxillule (Fig. 2B) as a blunt lobe bearing 3 larger outer setae, 2 smaller inner setae and on posterior surface 1 large patch of minute spinules. Maxilla (Fig. 3C) 2-segmented; proximal segment much wider than long, with 1 large distal protuberance covered entirely with minute spinules; distal segment blade-like and bluntly ended, with 2 small setae (1 on anterior and 1 on posterior surfaces) and transparent flange on cutting edge. Maxilliped (Fig. 2D) 4-segmented; first segment widest but very short and unarmed; second segment with 1 patch of minute spinules on medial surface; small third segment unarmed; terminal segment gradually narrowed distally, terminating in blunt tip covered with minute spinules, with 2 small setae.

Legs 1 and 2 (Fig. 2E, F) with 2-segmented rami and patches of spinules on coxa, basis and segments of rami. Distal spines on second exopodal segment of these legs with minute spinules along outer margin. Setae on these legs small and naked. Leg 3 (Fig. 2G) lobate, with 3 naked setae distally. Leg 4 (Fig. 2H) also lobate, tipped with 1 seta, and with distal patch of minute spinules near base of seta. Armature formula of legs 1-4 as follows:

Leg 5 (Fig. 3A) 2-segmented, consisting of protopod and 1-segmented exopod; protopod with 1 naked outer seta; exopod 222 67 Μm (ratio 3.31: 1), distally with several patches of minute spinules and 4 unequal, stiff setae; lengths of these setae 228, 433, 87, and 166 Μm, respectively, from outer to inner. Leg 6 probably represented by 1 small seta in genital aperture (Fig. 1B).

Male. Body (Fig. 3B) similar to that of female. Mean body length 1.79 mm (1.25-2.07 mm), based on 10 specimens. Prosomal somites gradually narrowed from anterior to posterior. Cephalothorax 438 404 Μm. Second to fourth pedigerous somites 154

Μm, respectively. Urosome 4-segmented as in female, and slightly shorter than prosome. Fifth pedigerous somite 175 283 Μm. Genital somite 154 233 Μm. Two free abdominal somites 125 Μm, respectively. Anal somite with minute spinules on ventral surface. Caudal rami slightly divergent; each ramus 156 62 Μm (ratio 2.52: 1), with 6 caudal setae, and spinules on ventral surface; largest terminal seta 620 Μm long, other 5 setae small.

Rostrum, antennule, and antenna not different from those of female. Mouthparts, except for maxilliped, as those of female. Maxilliped (Fig. 3C) massive and 4-segmented; first segment short and unarmed; second segment laterally expanded, with 1 large claw-like process and 1 spinules-covered bulge on medial margin and 1 small patch of minute spinules distally; third segment small and unarmed; terminal segment as strong claw, forming pincers along with medial process on second segment, and bearing 2 small setae proximally.

Legs 1-4 as in female. Leg 5 as in female, but exopod more slender than that of female. Leg 6 represented by 1 small seta on genital operculum (Fig. 3D).

Etymology. The specific name bipartita refers to the two-segmented abdomen in both sexes of the new species.

Remarks. Currently, genera of the Clausiidae are defined mainly by the leg morphology (Kim et al., 2013). With the reduced legs 3 and 4 which are represented by a setiferous lobe, the new species belongs to Indoclausia Sebastian and Pillai, 1974 which has comprised a single known species, I. bacescui Sebastian and Pillai, 1974. Although Sebastian and Pillai (1974) reported a scleractinian coral as host of I. bacescui, its true host is presumed to be a polychaete lived along with the coral. Indoclausia bipartita n. sp. differs from I. bacescui in the following points: (1) the abdomen is 2-segmented (vs. 4-segmented in I. bacescui); (2) the antenna is 3-segmented (vs. 4-segmented); (3) the distal segment of maxilla bears blade-like cutting edge (vs. distally bilobed and covered with spinules); (4) the maxilliped is distinctly 4-segmented (vs. obscurely segmented); and (5) legs 3 and 4 are tipped with 3 and 1 setae, respectively (vs. both tipped with 2 setae).

In copepods of the Clausiidae the abdomen is one- to four-segmented (generally four-segmented) in the female. The two-segmented abdomen of I. bipartita n. sp. is noticeable, because in the Clausiidae this feature is shared only with Sheaderia bifida Kim, Sikorski, O’Reilly and Boxshall, 2013. However, Sheaderia bifida is not related to the new species; this species from British waters has, unlike I. bipartita, a 5-segmented antennule, the 4-segmented antenna and female maxilliped, only a single distal spiniform element on the mandible, and no leg 3.