Asterocheres exilis, 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 : 244-247

publication ID	https://doi.org/ 10.12651/JSR.2024.13.2.185
persistent identifier	https://treatment.plazi.org/id/ED1887CB-FFC5-FFD5-FCF8-B0B3B38163EB
treatment provided by	Felipe
scientific name	Asterocheres exilis
status	sp. nov.

Treatment

Asterocheres exilis n. sp. ( Figs. 38 View Fig , 39 View Fig )

https://zoobank.org/urn:lsid:zoobank.org:act:0B8F0C

87-8A05-4DE0-AC4E-160A24A9560F

Type material. Holotype (♀; NIBRIV0000909871 ), intact paratypes (4♀♀; NIBRIV0000909872 ), and dissect- ed paratypes (2♀♀) from unidentified species of sponges, Dokdo Island (37°14 ʹ 17 ʺ N, 131°51 ʹ 59.7 ʺ E), SCUBA diving, depth 27 m, coll. T. Lee, 26 August 2023 GoogleMaps . Holotype and intact paratypes have been deposited in the National Institute of Biological Resources ( NIBR), Incheon, Korea. Dissected paratypes are kept in the collection of I.- H. Kim .

Etymology. The name exilis (from Latin exil, meaning “slender”) refers to the narrow body of the new species.

Female. Body ( Fig. 38A View Fig ) narrow. Mean body length 846 μm (818-900 μm), based on 7 specimens. Body length of figured and described specimen 830 μm. Prosome 527 × 349 μm. Cephalothorax 327 μm long, slightly wid- er than long. All prosomal somites with rounded lateral corners. Urosome ( Fig. 38B View Fig ) 4-segmented. Fifth pedigerous somite 114 μm wide. Genital double-somite 1.16 times longer than wide (136 × 117 μm), widest at proximal third; genital apertures positioned dorsolaterally at 40% region of double-somite length; post-genital lateral margins each bearing tuft of about 20 thin setules ( Fig. 39F View Fig ). Two free abdominal somites 48 × 74 and 38 × 65 μm, respectively. Anal somite bearing scattered spinules along posteroventral margin ( Fig. 38C View Fig ). Caudal ramus ( Fig. 38C View Fig ) much wider than long (21 × 30 μm), broadened distally, armed with 6 setae, and ornamented with small spinules along posteroventral margin; two medial distal setae (setae IV and V) thick, 233 and 265 μm long, respectively, other caudal setae much smaller.

Rostrum ( Fig. 38D View Fig ) as tapering ridge between antennules, with thin sclerotization along lateral margins. Antennule ( Fig. 38E View Fig ) 244 μm long, 19-segmented; 1st, 9th, and 2 terminal segments bearing 1 seta, 5 setae, 2 setae + aesthetasc, and 13 setae, respectively, all other segments each with 2 setae; all setae naked, mostly small. Antenna ( Fig. 38F View Fig ) with short coxa; basis 77 μm long, unarmed, unornamented; exopod 9 × 4.5 μm, bearing 1 proximal and 2 distal small setae; endopodal segments with 0, 1, and 2 setae, respectively; first endopodal segment 55 μm long, with setules along outer margin; terminal claw rather thick, 56 μm long, bearing several minute, scattered spines.

Oral siphon ( Fig. 38G View Fig ) 209 × 60 μm, narrow, extending to proximal margin of intercoxal plate of leg 1; proximal third slightly broadened. Mandibular stylet ( Fig. 38H View Fig ) 188 μm long, curved and broadened at distal third, bearing row of 6 teeth at distal region; palp ( Fig. 38I View Fig ) small, 22 μm long, tipped with 1 rudimentary seta (13 μm long) and 1 longer seta (104 μm long); palp plus longer distal seta (126 μm) only 0.67 times as long as stylet. Maxillule ( Fig. 38J View Fig ) bilobed; shorter outer lobe 25 μm long, bearing 3 setae, subdistal one of them pinnate, 64 μm long, other 2 setae naked, 77 and 70 μm long, respectively; inner lobe about 70 μm long, bearing 4 weakly pinnate setae distally, lengths of these 4 setae 110, 127, 106, and 50 μm, respectively, from inner to outer. Maxilla ( Fig. 38K View Fig ) 2-segment- ed; proximal segment bearing excretory pore proximally, unornamented; distal segment 1.35 times longer than proximal segment, slender, arched, with rows of spinules. Maxilliped ( Fig. 38L View Fig ) consisting of syncoxa, basis, and 3-segmented endopod; armature formula 1, 1, 2, 2, and 1+ claw; seta on basis vestigial, hardly visible; terminal segment and claw 44 and 59μm long, respectively.

Legs 1 ( Fig. 39A View Fig ), 2 ( Fig. 39B View Fig ), 3, and 4 ( Fig. 39D View Fig ) biramous with 3-segmented rami. Leg 3 similar to leg 2, except bearing 1 spine and 3 setae on third endopodal segment ( Fig. 39C View Fig ). Inner coxal seta absent in leg 1, but well-developed and pinnate in legs 2-4. Outer seta on basis small, translucent in all swimming legs. Leg 1 basis with broad inner distal seta, few spinules at inner distal corner, and row of thin spinules on distal margin near base of inner distal seta. Third endopodal segment of leg 3 with 1 spine and 5 setae ( Fig. 39C View Fig ), otherwise leg 3 similar to leg 2. Most of spines on swimming legs broadened, leaf-like. Armature formula for legs 1-4 as follows:

Coxa Basis Exopod Endopod

Leg 1 0-0 1-1 I-1; I-1; III, 2, 2 0-1; 0-2; 1, 2, 3 Leg 2 0-1 1-0 I-1; I-1; III, I, 4 0-1; 0-2; 1, 2, 3 Leg 3 0-1 1-0 I-1; I-1; III, I, 4 0-1; 0-2; 1, 1 +I, 3 Leg 4 0-1 1-0 I-1; I-1; III, I, 4 0-1; 0-2; 1, 1 +I, 2

Leg 5 ( Fig. 39E View Fig ) consisting of dorsolateral seta on fifth pedigerous somite and free exopod; exopodal segment sub-fusiform, 2.03 times longer than wide (63 × 3 μm), armed with 3 pinnate setae distally; lengths of distal setae 26, 27, and 45 μm, respectively, from outer to inner; innermost seta longest. Leg 6 ( Fig. 39F View Fig ) represented by 1 pinnate seta and 1 small spinule on genital operculum.

Male. Unknown.

Remarks. Asterocheres exilis n. sp. belongs to a group of Asterocheres characterized by the loss of the inner coxal seta on leg 1. This group comprises four known species: A. banderaae , A. eugenioi , A. sarsi , and A. trisetatus ( Bandera & Conradi, 2014; 2016; Kim & Lee, 2023). However, A. exilis n. sp. is readily differentiated from the four congeners by having (1) a narrow body (vs. the body is broad or moderately broad in the four congeners), (2) a genital double-somite which is distinctly longer than wide (vs. wider than long in the four congeners), and (3) 19-segmented female antennule (vs. 20- or 21-segmented in the four congeners). As additional diagnostic features of A. exilis n. sp., the outer lobe of the maxillule is armed with three setae only, and all the setae on the exopod of leg 5 are pinnate and its innermost seta is longer than the other two setae.