Aphotopontius kiost, 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 : 302-306

Aphotopontius kiost n. sp.

(Figs 1–3)

http://zoobank.org/ 61F57C32-00BE-496D-9A72-C9D00C09A7AA

Type material. Eleven females and three males from sediments at GTV1809 (11°24.883´S, 65°25.425´E, depth 2022 m), the Onnuri vent field ( OVF) on the Central Indian Ridge in the Indian Ocean, 23 June 2018. Holotype (female, MABIK CR00244725 ) and paratypes (eight females and two males, MABIK CR00244726 ) have been deposited in the Marine Biodiversity Institute of Korea ( MABIK), Seocheon. Dissected paratypes (two females and one male) are retained in the collection of the junior author.

Additional material examined. Forty-three females and nine males (one female and one male dissected) from washings of invertebrates (unidentified gastropods, bivalves and crustacean decapods) at GTV 1702 (19°33.387´S, 65°50.893´E, depth 2507 m), the Solitaire vent area on the Central Indian Ridge, 01 August 2017; 20 females from washings of invertebrates at GTV1807 (19°33.395´S, 65°50.889´E, depth 2634 m), the Solitaire vent area on the Central Indian Ridge, 20 June 2018 .

Female. Body (Fig. 1A) dorsoventrally flattened, 1.01 mm long in dissected paratype. Greatest width 515 μm across cephalothorax. Prosome 612 μm long, consisting of cephalothorax and three pedigerous somites. Posterolat- eral corners of cephalothorax pointed, those of three metasomal somites blunt or rounded. Ratio of length to width of prosome 1.19:1. Urosome (Fig. 1B) 5-segmented. Fifth pedigerous somite (first urosomal somite) 124 μm wide. Genital double-somite 128 × 146 μm, wider than long, with expanded proximal 1/3; genital aperture located dor- sally at level of widest area at anterior third; lateral apex of this widest area blunt. Three free abdominal somites 46 × 93, 31 × 78, and 47 × 70 μm, respectively. Anal somite ornamented with two rows of spinules on ventral surface near posteroventral margin (Fig. 1C). Anal area located between anal somite and caudal rami. Caudal rami (Fig. 1C) close to each other, 83 × 29 μm, 2.86 times as long as wide, with six setae (setae II–VII) and triangular, serrate lamella on posteroventral margin; two mid-terminal setae pinnate, other four smaller setae naked.

Rostrum absent. Antennule (Fig. 1D) 288 μm long, 13-segmented; first segment being longest, fifth segment second longest; armature formula 15, 7, 1, 2, 4, 2, 2, 2, 2, 2 + aesthetasc, 2, 3, and 7 + aesthetasc; distal seta on fifth segment pinnate, other setae naked; aesthetasc on terminal segment small, indistinct. Antenna (Fig. 1E) with short, unarmed coxa; basis with row of several spinules near base of exopod. Exopod 22 × 7.8 μm, about 2.8 times as long as wide, with elongate distal and two shorter subdistal setae. Endopod 2-segmented; proximal segment unarmed, ornamented with row of spinules on outer margin; distal segment about half as long as proximal segment, armed with two spinulose spines (60 and 33 μm long, respectively), one distal, one lateral setae; distal half ornamented with spinules.

Oral cone short, stout. Mandible (Fig. 1F) represented by simple, flattened stylet bearing about ten teeth distally and hyaline lamella along both margins. Maxillule (Fig. 1G) bilobed; outer lobe slightly shorter than inner lobe, with two distal and one subdistal setae; broader inner lobe with four setae distally and setules along inner margin. Maxilla (Fig. 1H) 2-segmented; proximal segment (syncoxa) unarmed but with basal pore; claw-like distal segment (basis) attenuated, with spinules (or setules) distally; large, spinulose seta present, arising between segments, with proximal articulation. Maxilliped (Fig. 1I) consisting of syncoxa, basis, and 2-segmented endopod; syncoxa subrectangular, with naked inner distal seta; basis with small inner seta and short setules on outer margin; proximal and distal endopodal segments armed with three and one setae, respectively; all setae naked; terminal claw weakly arched, 73 μm long, 2.2 times as long as distal endopodal segment, spinulose along inner margin.

Legs 1–3 (Fig. 2A–C) biramous, with 3-segmented rami. Leg 4 (Fig. 2D) with 3-segmented exopod and 2-segmented endopod. Inner coxal seta present in legs 1–3, but absent in leg 4. Inner spine on basis of leg 1 well-developed, spinulose, 43 μm long, extending to distal margin of first endopodal segment. Proximal and distal segments of leg 4 endopod 34 × 23 and 63 × 24 μm, respectively; distal segment with setules on outer and inner margins, its terminal spine setiform and 69 μm long. Armature formula for legs 1–4 as follows:

Coxa Basis Exopod Endopod

Leg 1: 0-1 1-I 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, 5 0-1; 0-2; 1, I, 3

Leg 4: 0-0 1-0 I-1; I-1; III, I, 4 0-1; 0, I, 1

Leg 5 (Fig. 2E) unsegmented, but divisible by dorso-medial, non-sclerotized area into protopod and exopod; protopod about 37 × 18 μm, with elongate, naked dorsal seta; exopod 39 × 17 μm, about 2.3 times as long as wide, with three distal pinnate setae, longest one of latter three 100 μm long. Leg 6 (Fig. 2F) represented by short pinnate and minute setae in genital aperture.

Male. Body (Fig. 3A) narrower than that of female. Length of dissected paratype 644 μm. Prosome 395 μm long, with greatest width 304 μm. Cephalothorax 259 μm long. Urosome 6-segmented. Genital somite 67 × 88 μm, distinctly wider than long, with rounded corners. Four abdominal somites 41 × 52, 27 × 46, 20 × 41, and 27 × 40 μm, respectively. Anal somite with scattered spinules on posteroventral area. Caudal ramus (Fig. 3B) 41 × 17 μm, 2.41 times as long as wide, with serrate posteroventral margin.

Antennule (Fig. 3C) 11-segmented and curved medially; armature formula 1, 13, 7, 1 + spine, 2, 4, 2, 2, 2, aesthetasc, and 11. Fourth segment with strong outgrowth on anterior margin; spine on this segment with two longitudinal rows of spinules. Aesthetasc on penultimate segment relatively small, not extending beyond distal end of terminal segment.

Antenna, mandible, maxillule, maxilla, maxilliped, and legs 1–4 as in female.

Leg 5 (Fig. 3D) 2-segmented, but protopod (proximal segment) fused with somite, with elongate outer seta. Free exopod nearly quadrate, 20 × 17 μm, with three simple outer setae and two distal, knife-like setae; latter two setae 27 (ventral) and 26 μm (dorsal) long. Leg 6 (Fig. 5E) represented by two naked setae on spinulose genital operculum.

Etymology. The specific name kiost (noun) used in apposition is the abbreviation of the Korea Institute of Ocean Science and Technology (KIOST).

Remarks. In Aphotopontius kiost n. sp., the inner coxal setae are present in legs 1–3, but absent in leg 4. This feature is shared by other four congeners only: A. acanthinus Humes and Lutz, 1994 , A. atlanteus Humes, 1996 , A. flexispinus Humes, 1987 , and A. mammillatus Humes, 1987 . Aphotopontius kiost n. sp. is distinguishable from these four species by the different length/width ratio of the female caudal ramus; this ratio is 2.86 in A. kiost n. sp., whereas it is less than 2.0 in A. acanthinus and A. atlanteus , 4.2 in A. flexispinus , and 2.12 in A. mammillatus (see Humes and Lutz 1994; Humes 1987, 1996). As additional discrepant features, A. atlanteus , A. flexispinus and A. mammillatus have rounded lateral margins in the expanded anterior part of the genital double-somite, in contrast to A. kiost n. sp., in which the lateral margin bears an angular apex. Furthermore, A. acanthinus and A. mammillatus have a pointed inner distal extension on the basis of leg 1, in contrast to the absence of any pointed extension on the same region in A. kiost n. sp.

FIG. 1. Aphotopontius kiost n. sp., female. A, habitus, dorsal; B, urosome, dorsal; C, caudal rami, ventral; D, antennule; E. antenna; F, mandible; G, maxillule; H, maxilla; I, maxilliped. Scale bars: A = 0.2 mm; B = 0.1 mm; C, E–H = 0.02 mm; D, I = 0.05 mm.

FIG. 2. Aphotopontius kiost n. sp., female. A, leg 1; B, leg 2; C, leg 3; D, leg 4; E, leg 5; F, genital aperture. Scale bars: A–D = 0.05 mm; E, F = 0.02 mm.

FIG. 3. Aphotopontius kiost n. sp., male. A, habitus, dorsal; B, left caudal ramus, ventral; C, antennule; D, left leg 5, ventral; E, left genital operculum. Scale bars: A = 0.1 mm; B–E = 0.02 mm.