Acontiophorus enneamerus, Lee, 2025

Lee, Il-Hoi Kim and Taekjun, 2025, Ten new species of siphonostomatoid copepods (Crustacea) associated with marine invertebrates from Korea, Journal of Species Research 14 (2), pp. 146-181 : 150-153

Acontiophorus enneamerus n. sp. ( Figs. 3 , 4 )

https://zoobank.org/urn:lsid:zoobank.org:act:423DB17F-

1DE3-4D75-83A7-77B939367B20

Type material. Holotype (intact ♀; MABIK CR002577 87), intact paratype (♀; MABIK CR00257788 ), and dissected paratype (♀) from washings of mixed species of sponges, at Munseom , Seogwipo, Jeju Island (33°13 ʹ 39.4 ʺ N, 126°33 ʹ 48.2 ʺ E), at a depth of 56 m, collected by Taekjun Lee, on 25 April 2023. The holotype and intact paratype have been deposited in the National Marine Biodiversity Institute of Korea ( MABIK), Seocheon. The dissected paratype is held in the collection of I.-H. Kim.

Etymology. The specific name is derived from the Greek enne (= nine) and mero (= part), alluding to the nine-segmented antennule in the female.

Female. Body ( Fig. 3A ) tapering posteriorly. Body length of dissected paratype 665 μm. Prosome 448 μm long. Cephalothorax 300× 348 μm, distinctly wider than pedigerous somites. All prosomal somite with rounded posterolateral corners. Urosome ( Fig. 3B ) 4-segmented. Fifth pedigerous somite 95 μm wide. Genital double-somite 0.84 times as long as wide (79 × 94 μm), widest at anterior 34% region, followed by evenly tapering posterior part; genital apertures positioned dorsolaterally at region just posterior to widest region; posterolateral region of genital apertures bearing pointed process ( Fig. 4G ). Two free abdominal somites 34 × 48 and 28 × 47 μm, respectively. Anal somite ( Fig. 3D ) ornamented with 2 oblique rows of 9 thick setules on ventral surface. Caudal ramus ( Fig. 3C ) 1.91 times longer than wide (42× 22 μm), armed with 6 setae and ornamented with several small spinules on mediodorsal surface and 6 thick setules on medioventral surface ( Fig. 3D ); seta VI tipped on digitiform process.

Rostrum absent. Antennule ( Fig. 3E ) short, 102 μm long, 9-segmented; armature formula 2, 14, 6, 2, 6, 3, 1 + aesthetasc, 5, and 7; setae densely arranged; aesthetasc on seventh segment shorter than total length of segments. Antenna ( Fig. 3F ) with unarmed coxa; basis bearing long setules at inner distal corner and on subdistal inner margin; exopodal segment 3.0 times longer than wide (33 × 11 μm), bearing 1 small seta near middle and 1 large, pinnate seta and 1 spiniform process distally; first endopodal segment 17 μm long, unarmed; second endopodal segment 23 μm long, armed with 5 very unequal setae consisting of 1 proximal pinnate seta, 2 broad, spiniform setae covered with numerous spinules all over (longer distal one 65 μm long and shorter subdistal one 43 μm long), 1 small distal seta, and 1 finely spinulose subdistal seta.

Oral siphon ( Fig. 3G ) bendable, extremely long, 622 μm long, extending to distal margin of caudal rami, consisting of tapering proximal 15% and thin distal 85%. Mandible ( Fig. 3H ) consisting of thread-like stylet and unsegmented palp; palp bearing 1 small spinule-like setule and tipped with large, plumose seta; latter seta not articulated from palp segment. Maxillule ( Fig. 3I ) bilobed; outer lobe 15 × 15 μm, with 1 small, naked seta and 3 larger pinnate seta; inner lobe 22 × 18 μm, with 5 unequal setae, 2 of them pinnate, remaining 3 naked. Maxilla ( Fig. 3J ) 2-segmented, ornamented as in A. decamerus n. sp. Maxilliped ( Fig. 4A ) 5-segmented; armature formula 1, 0, 2, 2, and 1; first segment (completely fused precoxa and coxa) 64 μm long, with spinules on outer margin; second segment (basis) also 64 μm long, bearing spinules on outer margin; terminal segment 27 μm long, terminal claw 57 μm long, bearing fine spinules along concave margin.

Leg 1 ( Fig. 4B ) lacking inner coxal seta. Armature formula of legs 2-4 ( Fig. 4C- E ) as in A. decamerus n. sp. Leg 4 with moderately long outer seta on basis. Leg 5 ( Fig. 4F ) consisting of protopod and free exopod; protopod fused with somite as long as wide, with 1 weakly pinnate outer distal seta and 1 small, naked inner distal seta; exopodal segment small, 1.11 times longer than wide (20 × 18 μm) armed with 5 setae (1 pinnate outer subdistal, 1 pinnate and 1 naked distal, and 2 shorter pinnate inner). Leg 6 ( Fig. 4G ) as 1 naked seta and 1 spinule on genital operculum.

Male. Unknown.

Remarks. Acontiophorus enneamerus n. sp. closely resembles A. pilosus Kim & Je, 2000 , which is associated with a bryozoan in Korea ( Kim & Je, 2000). Both species share the absence of the inner seta on the coxa of leg 1, and have a nine-segmented female antennule, a feature possessed only by them and A. usuaiensis Johnsson, 2001 . They also have similarly proportioned female caudal rami. However, they cannot be identified as the same species due to several significant distinctions: (1) the presence of a pointed process on the lateral margin near the genital aperture in A. enneamerus n. sp., which is absent in A. pilosus ; (2) a smooth lateral margin of the caudal ramus in A. enneamerus n. sp., as opposed to a pinnate margin in A. pilosus ; (3) the two large terminal spiniform elements of the antenna are uniformly spinulose in A. enneamerus n. sp., whereas in A. pilosus they display two or more rows of spinules; (4) the largest terminal spiniform element of the antenna in A. enneamerus n. sp. is about 2.9 times longer than its terminal segment, while it is only about 2.0 times longer in A. pilosus ; and (5) the female adult body of A. enneamerus n. sp. measures approximately 0.67 mm, smaller than the 0.92 mm reported for A. pilosus in the original description ( Kim & Je, 2000). These differences have been validated through re-examination of newly collected specimens of A. pilosus .

Figures

Fig. 3. Acontiophorus enneamerus n. sp., female. A, habitus, dorsal; B, urosome, dorsal; C, left caudal ramus, dorsal; D, anal somite and caudal rami, ventral; E, antennule; F, antenna; G, oral siphon; H, mandible; I, maxillule; J, maxilla. Scale bars:A, 0.1mm; B, G, 0.05mm; C-F, H-J, 0.02mm.

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