Asterocheres serratus Lee, 2024, n. sp.

Asterocheres serratus n. sp. (Figs. 24-26) https://zoobank.org/urn:lsid:zoobank.org:act:C5D1EC 62-31AF-4D5B-86B4-11A9CCF90842 Type material. Holotype (intact ♀; MABIK CR00254 666), intact paratypes (10♀♀, 1♂; MABIK CR0025 4667), and dissected paratypes (1♀, 1♂) from unidentified sponges, at Seopseom, Seogwipo, Jeju Island (33°13 ʹ 39.6 ʺ N, 126°35 ʹ 58.9 ʺ E), trimix diving, depth 50.1 m, coll. T. Lee, 25 May 2022. Holotype and intact paratypes has been deposited in the Marine Biodiversity Institute of Korea (MABIK), Seocheon. Dissected paratypes are kept in the collection of I-H. Kim. Etymology. The specific name is taken from its key character, the serrate lateral margins of the fourth pedigerous somite. Female. Body (Fig. 24A) rather small. Body length 603 μm long in dissected and described specimen. Mean body length 601 μm (538-640 μm), based on 9 specimens. Prosome 424 μm long. Cephalothorax wider than long (280 × 327 μm). Posterolateral corner of cephalothorax angular. Second to fourth pedigerous somites with rounded lateral corners. Fourth pedigerous somite characteristically serrate along lateral margins. Urosome (Fig. 24B) 4-segmented. Fifth pedigerous somite 89 μm wide, bearing scattered spinule on lateral and dorsolateral surfaces and row of fine spinules along posterodorsal margin. Genital double-somite wider than long (70 × 83 μm), consisting of expanded anterior three quarters and narrower posterior quarter; genital apertures positioned dorsolaterally near midway of double-somite length; postgenital lateral margin bearing 14 or 15 spinules of unequal lengths (Fig. 25F); posteroventral margin with row of spinules. Two free abdominal somites subequal in length, 26 × 47 and 27 × 39 μm, respectively. Anal somite with row of spinules on posteroventral somite (Fig. 24C). Caudal ramus (Fig. 24C) 0.90 times longer than wide (18 × 20 μm), armed with 6 setae and ornamented with row of spinules along posteroventral margin. Rostrum (Fig. 24D) as tapering ridge between antennules, without defined distal apex. Antennule (Fig. 24E) 305 μm long, 21-segmented; segments each armed with 2 setae, except 7 setae on 9th segment, 2 setae + aesthetasc on 18th segment, 4 setae on penultimate segment and 7 setae on terminal segment; some of setae on proximal segments weakly pinnate or truncated and tipped with minute setule. Antenna (Fig. 24F) as usual for genus; first endopodal segment 50 μm long; terminal claw 54 μm long, slightly longer than first endopodal segment; spinules near exopod of basis distinct, not needle-like. Oral siphon (Fig. 24G) 168 × 47 μm, rather slender, its distal tip reaching mid-region between maxilliped and leg 1. Mandible (Fig. 24H) bearing slender coxal stylet and palp; stylet 152 μm long, bearing about 10 minute teeth along distal region; palp 1-segmented, 45 μm long, tipped with 2 naked setae; setae 128 and 55 μm long, respectively; palp plus longer distal seta 173 μm long, 1.14 times longer than stylet. Maxillule (Fig. 24I) bilobed; inner lobe about 50 μm long, tipped with 4 long and 1 small setae (4 long setae 103, 102, 90, and 56 μm long, respectively); outer lobe about 18 μm long, bearing 4 naked setae (lengths of these setae 64, 55, 40, and 23 μm long, respectively). Maxilla (Fig. 24J) slender; proximal segment with row of about 10 spinules proximally; distal segment longer than proximal segment, bearing linguiform process proximally and row of minute spinules along distal third. Maxilliped (Fig. 24K) with armature formula 1, 0, 2, 1, 1, and 1 + claw; basis with several spinules on outer margin and few setae on subdistal part of inner margin; first endopodal segment with 2 spinules on outer margin; terminal segment and claw 25 and 64 μm, respectively. Legs 1 (Fig. 25A), 2 (Fig. 25B), 3, and 4 (Fig. 25D) armed as usual for genus; inner coxal seta present in all these legs. Leg 3 similar to leg 2, except bearing 1 spine and 5 setae on third endopodal segment. Intercoxal plate bearing spinules and setules in leg 1, spinules only in leg 2, but smooth in legs 3 and 4. Inner coxal seta of leg 1 slender and naked, that of leg 4 rudimentary. Outer margin of coxa spinulose in legs 1-4. Armature formula for legs 1-4 as in A. aesthetes. Leg 5 (Fig. 24B) consisting of 1 long dorsolateral seta on fifth pedigerous somite and exopod; exopodal segment (Fig. 25E) nearly rectangular, 2.60 times longer than wide (52 × 20 μm), bearing many spinules on outer and inner margins, and armed with 2 long, equal setae (outer and inner setae 90 and 92 μm long, respectively), and small, naked inner subdistal seta (21 μm long). Leg 6 as 1 pinnate seta and 1 spinule on genital operculum. Male. Body (Fig. 26A) smaller and narrower than that of female. Body length 505 μm in figured and dissected specimen. Prosome 340 μm long. Cephalothorax slightly wider than long (227 × 248 μm). Fourth pedigerous somite with serrated lateral margin as in female. Urosome 5-segmented. Genital somite(Fig. 26B) 73 × 82 μm, with few spinules on lateral margins and dorsal posterolateral corners. Three abdominal somites 15 × 45, 14 × 38, and 26× 30 μm, respectively. Caudal ramus 16 × 15 μm. Rostrum as in female. Antennule (Fig. 26C) 18-segmented; segments each with 2 setae, except 7 setae on 9th segment, 2 setae + aesthetasc on penultimate segment, and 11 setae on terminal segment; no aesthetasc present on 13th segment. Antenna as in female. Oral siphon, mandible, maxillule, and maxilla as in female. Maxilliped with proximal process on inner margin of basis. Legs 1 and 4 as in female. Leg 2 endopod prominently different from that of female: distal one of two dentiform processes on outer distal corner of second segment elongated (Fig. 26D); its third segment armed with 1 seta on outer margin, 2 slightly curved, attenuated distal processes, 1 proximally swollen seta and 1 unilaterally spinulose spine on distal margin, and 3 pinnate setae on inner margin. Third endopodal segment of leg 3 slightly different from that of female in having shortened outer seta on distal margin (Fig. 26E). Leg 5 armed as in female; exopodal segment (Fig. 26F) with 3 setae, 2.5 times longer than wide (25 × 10 μm), ornamented with spinule on inner and outer margins; lengths of 3 setae 34, 42, and 20 μm, respectively, from outer to inner. Leg 6 (Fig. 26B) represented by 2 unequal setae and pointed distal process on genital operculum. Remarks. Asterocheres serratus n. sp. is readily recognizable by its key character, the serrate lateral margins of the fourth pedigerous somite, which has not been reported until now in Asterocheres. The unusually long setae of female leg 5 (except the short inner seta of the exopod) and the typical, sexually dimorphic form of the endopod of male leg 2 are also diagnostic features of the new species.