Asterocheres eurychelatus, Lee, 2024

Lee, Il-Hoi Kim and Taekjun, 2024, Copepods of the genus Asterocheres Boeck, 1859 (Siphonostomatoida: Asterocheridae) from Korean waters, Journal of Species Research 13 (2), pp. 185-254 : 210-212

Asterocheres eurychelatus n. sp. ( Figs. 14 , 15 )

https://zoobank.org/urn:lsid:zoobank.org:act:10ECAF

07-255F-4726-B1F3-F7EDA13A27DC

Type material. Holotype (intact ♀; MABIK CR0025 4233), intact paratypes (14♀♀; MABIK CR00254234 ), and dissected paratype (1♀) from washings of unidentified sponges, Gapado, Jeju Island (33°10 ʹ 20 ʺ N, 126° 17 ʹ 30 ʺ E), trimix diving, depth 36 m, coll. T. Lee , 27 April 2023 . Holotype and intact paratypes have been deposited in the Marine Biodiversity Institute of Korea ( MABIK), Seocheon, Korea. Dissected paratype is kept in the collection of I.-H. Kim .

Etymology. The specific name is a combination of the Greeks eury (= broad) and chel (= a claw), referring to the broad terminal claw of the antenna and maxilliped.

Female. Body ( Fig. 14A ) relatively small. Mean body length 624 μm (581-668 μm), based on 10 specimens. Figured and described specimen 655 μm long. Prosome 415 μm long, occupying 63% of body length. Cephalothorax 282 × 312 μm. All prosomal somites bearing rounded lateral corners. Urosome ( Fig. 14B ) 4-segment- ed. Fifth pedigerous 91 μm wide, as wide as genital double-somite. Genital double-somite 1.16 times longer than wide (106 × 91 μm) widest at proximal 32% region, evenly narrowing posteriorly from widest region; genital apertures positioned dorsolaterally at proximal 36% region; postgenital lateral margin with 11 or 12 equally small spinules ( Fig. 15G ). Two free abdominal somites 45 × 52 and 30 × 50 μm, respectively; anal somite with fine spinules along posteroventral margin ( Fig. 14C ). Caudal ramus ( Fig. 14C ) wider than long (21 × 22 μm), with 6 setae and row of spinules on posteroventral margin.

Rostrum ( Fig. 14D ) as tapering ridge, lacking posterior apex. Antennule ( Fig. 14E ) 223 μm long, 20-segmented; 9th, 18th, and terminal segments with 7 setae, 2 setae + aesthetasc, 11 setae, respectively, all other segments each with 2 setae; all setae naked. Antenna ( Fig. 14F, G ) with short, unarmed coxa; basis 61 μm long, unarmed but bearing longitudinal row of minute spinules; exopod small, 9× 4.8 μm, bearing 3 small setae; first endopodal segment 45 μm long, unarmed but bearing longitudinal row of small spinules; second endopodal segment short, with 1 spiniform seta subdistally; third endopodal segment 16 μm long, distally with 1 spine (18 μm long) and 1 small seta and terminated in robust claw of 35 μm long.

Oral siphon ( Fig. 14H ) 127 × 61 μm, reaching insertions of maxillipeds. Mandibular stylet ( Fig. 14I ) 120 μm long, bearing 6 denticles arranged longitudinally at distal region; palp slender, 1-segmented, 41 μm long, tipped with 1 long (90 μm long) and 1 short (34 μm long) setae; palp segment plus its longer distal seta 131 μm long, 1.09 times longer than stylet. Maxillule ( Fig. 14J ) bilobed; small outer lobe 17 μm long, distally with 4 setae (lengths of these setae 54, 49, 43, and 22 μm, respectively); inner lobe about 55 μm long, about 3.2 times longer than outer lobe, tipped with 1 minute and 4 large setae (lengths of 4 large setae 63, 62, 58, and 40 μm, respectively). Maxilla ( Fig. 14K ) 2-segmentd; proximal segment bearing row of about 10 spinules at proximal region; distal segment (chela) about 1.2 times longer than proximal segment, bearing row of minute spinules along distal third. Maxilliped ( Fig. 15A ) 6-segmented; armature formula 1, 1, 2, 1, 1, and 1+ claw; second segment (basis) 73 μm long; terminal segment 30 μm long, its distal seta spiniform; terminal claw 47 μm long, robust, 1.57 times longer than terminal segment.

Legs 1 ( Fig. 15B ), 2 ( Fig. 15C ), 3, and 4 ( Fig. 15E ) biramous, with 3-segmented rami. Distal margin of intercoxal plate bearing several spinules in leg 1, setules in leg 2, but smooth in legs 3 and 4. Inner distal seta on basis of leg 1 broad. Second endopodal segment of legs 1-4 with bicuspid outer distal corner. Leg 3 same as leg 2, except bearing 1 spine plus 5 setae on third endopodal segment ( Fig. 15D ). Leg 4 lacking inner coxal seta. Distal spine on third endopodal segment of leg 3 and 4 fusiform, shorter than segment. Armature formula for legs 1-4 as in A. processus n. sp.

Leg 5 ( Fig. 14B ) consisting of dorsolateral seta on fifth pedigerous somite and exopod. Exopodal segment ( Fig. 15F ) 1.89 times longer than wide (36 × 19 μm), fusiform, bearing 3 naked setae (31, 36, and 31 μm long, respectively, from outer to inner), and ornamented with few spinules on inner and outer margins. Leg 6 ( Fig. 15G ) represented by 2 small, unequal setae and 1 small denticle on genital operculum.

Male. Unknown.

Remarks. As a combination of diagnostic features of A. eurychelatus n. sp. (1) the caudal ramus is short, not longer than wide; (2) the antennule of the female is 20-segmented; (3) the mandibular palp is 1-segmented; and (4) leg 4 lacks an inner seta on the coxa. The new species shares this combination of the diagnostic features with six congeners: A. siphonatus ; A. proboscideus Stock, 1966 ; A. stocki Nair & Pillai, 1984 ; A. banderaae ; A. processus n. sp.; and A. bulbosus Malt, 1991 . The first three species are easily separated from the new species by their unusually long oral siphon, which extends beyond leg 4 in A. siphonatus as in the redescription in the present paper, over the caudal rami in A. proboscideus (see Stock, 1966), and to leg 5 in A. stocki (see Nair & Pillai, 1984). Asterocheres banderaae and A. processus differ from the new species in lacking an inner coxal seta on leg 1. Asterocheres bulbosus also differs from the new species in having only one seta on the first segment of the antennule as described and illustrated by Malt (1991), which was confirmed by Bandera & Conradi (2009b) (vs. two setae in the new species).

At least one of the above four diagnostic features is unknown in A. corneliae Schirl, 1973 ; A. dentatus Giesbrecht, 1987 ; and A. minor Thompson & A. Scott, 1903 . As important differences of these species from the new species, the oral siphon of A. corneliae is much thinner than that of the new species and reaches leg 1 ( Schirl, 1973), the prosome of A. minor is circular and its abdominal somites are longer than wide as illustrated by Thompson & Scott (1903), and the genital double-somite of the female of A. dentatus bears a pointed process on the lateral margins ( Giesbrecht, 1899).

The form of the terminal claw of the antenna and maxilliped of A. eurychelatus n. sp. is remarkable, since it is unusually broadened, a very rare feature within the genus.

Figures

Fig. 14. Asterocheres eurychelatus n. sp., female. A, habitus, dorsal; B, urosome, dorsal; C, caudal rami, dorsal; D, rostral area, ventral; E, antennule; F, antenna; G, distal part of antenna; H, oral siphon; I, mandible; J, maxillule; K, maxilla. Scale bars: A, 0.1 mm; B, 0.05 mm; C-K, 0.02mm.

Fig. 15. Asterocheres eurychelatus n. sp., female.A, maxilliped; B, leg 1; C, leg 2; D, endopod of leg 3; E, leg 4; F, exopod of leg 5; G, left side of genital double-somite, dorsal. Scale bars: 0.02mm.