Aphotopontius muricatus, Lee & Kim & Kim, 2020

Lee, Jimin, Kim, Dongsung & Kim, Il-Hoi, 2020, Copepoda (Siphonostomatoida: Dirivultidae) from Hydrothermal Vent Fields on the Central Indian Ridge, Indian Ocean, Zootaxa 4759 (3), pp. 301-337 : 306-309

Aphotopontius muricatus n. sp.

(Figs 4, 5)

http://zoobank.org/ 11F0AA95-F0EE-4D2B-9BF7-6E1B6355513A

Material examined. One female (holotype, MABIK CR00244727 , dissected and mounted on a slide) from washings of invertebrates, at GTV1807 (19°33.395´S, 65°50.889´E, depth 2634 m), the Solitaire hydrothermal vent area on the Central Indian Ridge in the Indian Ocean, 20 June 2018. Holotype was deposited in the Marine Biodiversity Institute of Korea ( MABIK), Seocheon.

Female. Body (Fig. 4A) broad, flattened, 1.25 mm long. Greatest width 644 μm across cephalothorax. Prosome 753 μm long. Cephalothorax and three metasomal somites acutely pointed at posterolateral corners, 644, 531, 438, and 261 μm wide, respectively. Ratio of length/ width of prosome 1.17:1. Urosome (Fig. 4B) 5-segmented. Fifth pedigerous somite (first urosomal somite) 84 × 175 μm, its posterolateral parts extended laterally, with angular distal corners. Genital double-somite 168 × 139 μm, 1.21 times longer than wide, constricted in middle of lateral margins, with dentiform process at posterolateral corners; genital aperture positioned dorsolaterally at 35% length of doublesomite. Three abdominal somites 57 × 82, 23 × 71, and 57 × 66 μm, respectively; second abdominal somite less than half as long as first and anal somites. Anal somite (Fig. 4C) ornamented with scattered spinules on distal half of ventral surface. Caudal rami (Fig. 4C) elongate, close to each other, 6.61 times as long as wide (152×23 μm); armed with six setae, deduced from scars of setae, all of them positioned distally or subdistally.

Rostrum weak, easily destroyed, semicircular, with round posterior margin. Antennule (Fig. 4D) slender, longer than cephalothorax, 565 μm long, 12-segmented; articulation obscure between terminal and penultimate segments; first segment being longest and third segment shortest; armature formula 15,10, 2, 4, 2, 2, 2, 2, 2 + aesthetasc, 1, 4, and 7; larger setae on first and second segments with multiple annulations; all setae naked. Antenna (Fig. 4E) slender, consisting of short, unarmed coxa, basis, 1-segmented exopod, and 2-segmented endopod; basis 128 × 30 μm, with longitudinal row of minute spinules along distal half. Exopod elongate, 8.4 times as long as wide (76 × 9 μm), about 0.6 times as long as basis; with one terminal and two small subterminal setae. First endopodal segment 91 × 23 μm, unarmed, but ornamented with longitudinal row of minute spinules along inner side. Second endopodal segment 39 × 17 μm, less than half as long as first endopodal segment, armed with elongate, setiform terminal spine (235 μm long) and four setae, three of latters small, and ornamented with few setules.

Oral cone short, stout. Mandible (Fig. 4F) represented by simple, flattened stylet bearing irregular teeth distally and hyaline lamella at distal third. Maxillule (Fig. 4G) bilobed; outer lobe 34 × 14 μm, with two distal and one subdistal setae; inner lobe 58 × 35 μm, with protruded inner margin and distally armed with five setae, one of them minute. Maxilla (Fig. 4H) 2-segmented; proximal segment (syncoxa) proximally with short, wrinkled tube bearing pore at tip and distally one large setiform extension bearing several stiff setules subdistally; distal segment (basis) elongate, attenuated, with tuft of setules in middle, minute spinules along distal third of inner margin, setules along distal outer margin, and tipped with one large setule. Maxilliped (Fig. 5A) slender; syncoxa and basis fused, without articulation between them, bearing two setae on inner margin, about ten minute spinules near distal third of outer margin and few setules at proximal outer margin; endopod thin, 3-segmented, 38, 53, and 45 μm long, respectively, with three, one, and one setae, respectively; seta on second endopodal segment large, almost as long as combined endopodal segments; terminal claw elongate, 152 μm long, about 3.4 times as long as third endopodal segment.

Leg 1 (Fig. 5B) with 3-segmented rami. Inner distal spine on basis slender, 64 μm long. Outer spines on exopod slender. First and second exopodal segments setulose along outer margin. Endopod setulose along outer margin and flexed inwards between first and second segments; first segment about 1.6 times longer than wide; second and third segments broadened; outer distal corner of second segment bicuspid; outer one of two distal setae and third inner seta on third segment distinctly smaller than other setae on segment; inner one of two distal setae and first and second inner setae on third segment rather blunt at tip, with fine spinules along distal third of outer margin.

Leg 2 (Fig. 5C) with 3-segmented rami; exopod spinulose along outer margin. First exopodal segment with patch of spinules on anterior surface near base of inner seta. Endopod setulose along outer margin. Second endopodal segment with bicuspid outer distal corner.

Leg 3 (Fig. 5D) also with 3-segmented rami. Basis with prominent, digitiform process (indicated by arrowhead in Fig. 5D) on distal margin between bases of rami. Exopod as in leg 2. Endopod also as in leg 2, except armature of third endopodal segment bearing one distal spine and one outer and three inner setae.

Leg 4 (Fig. 5E) with 3-segmented exopod and 2-segmented endopod. Coxa lacking inner seta. Basis with small, attenuated process on distal margin between bases of rami. Both rami slender. Endopod as long as first exopodal segment; first and second endopodal segments 43 and 64 μm long, respectively; distal spine on second endopodal segment 133 μm long, longer than endopodal segments.

Armature formula for legs 1–4 as in A. kiost n. sp.

Leg 5 (Fig. 5F) distinctly 2-segmented. Protopod (first segment) 1.24 times as long as wide (36 × 29 μm), with large outer distal seta (148 μm long). Exopod (second segment) 1.82 times as long as wide (31 × 17 μm), gradually widened distally, armed with one outer subdistal seta (75 μm long) and two distal setae (86 and 40 m long, respec- tively), shorter outer one of two latter naked, spiniform. Leg 6 (Fig. 5G) represented by one pinnate seta on genital operculum.

Male. Unknown.

Etymology. The specific name muricatus is derived from the Latin muricat (=pointed), referring to the pointed posterolateral corners of the cephalothorax and metasomal somites.

Remarks. Aphotopontius muricatus n. sp. is similar to A. mammillatus Humes, 1987 , which was redescribed by Ivanenko and Heptner (1998), in having a female genital double-somite that is distinctly longer than wide, with a constriction in the middle and a dentiform process at each posterolateral corner. Otherwise, the new species is readily separable from A. mammillatus and other congeners due to three striking morphological features: (1) the antenna bears an elongate exopod that is longer than half the length of the basis, (2) the syncoxa and the basis of the maxilliped are fused to each other, and (3) the endopod of leg 1 is flexed inwards.

FIG. 4. Aphotopontius muricatus n. sp., female. A, habitus, dorsal; B, urosome, dorsal; C, anal somite and caudal rami, ventral; D, antennule; E, antenna; F, mandible; G, maxillule; H, maxilla. Scale bars: A = 0.2 mm; B = 0.1 mm; C–E = 0.05 mm; F–H = 0.02 mm.

FIG. 5. Aphotopontius muricatus 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: A, F, G = 0.05 mm; B–E = 0.1 mm.