Archinotodelphys bimerus, Kim & Boxshall, 2020

Kim, Il-Hoi & Boxshall, Geoff A., 2020, A revision of the family Archinotodelphyidae Lang, 1949 (Copepoda: Cyclopoida Oithonida), with the recognition of 15 new species, Zootaxa 4801 (1), pp. 1-56 : 28-31

Archinotodelphys bimerus sp. nov.

(Figs. 15, 16)

Type material. Holotype (♂; MNHN-IU-2014-21201). Dissected paratype (♂) in the collection of IHK.

Type host. unidentified species of family Molgulidae .

Type locality. North Atlantic , America Basin, R. V. Atlantis II Cruise 24, Stn 126 (39°37’N, 66°45’W), depth 3806 m, 24 August 1966 .

Etymology. The name of the new species refers to the 2-segmented state of the maxillulary endopod.

Male. Body (Fig. 15A) slender; length 876 μm; prosome 447 μm long; cephalosome 212×248 μm, dorsal cephalosomic shield with posteriorly extended posterolateral corners. Urosome 6-segmented: fifth pedigerous somite 47×87 μm; genital somite sub-square, 75×90 μm; 4 abdominal somites 47×56, 32×48, 32×46, and 48×46 μm, respectively; anal somite ornamented with spinules along posteroventral margin, rather deep postero-median incision, and nipple-shaped process at both sides of incision (indicated by arrowhead in Fig. 15C). Caudal ramus (Fig. 15C) about 6.0 times longer than wide (99×16 μm), ornamented with spinules along posteroventral margin and armed with 6 setae; outer lateral seta pinnate and located at midlength of ramus; other 5 setae naked.

Rostrum (Fig. 15D) tapering, 73×47 μm. Antennule (Fig. 15E) 278 μm long and 16-segmented, with genicula- tion between segments 14 and 15; terminal segment pointed at tip; armature formula 3, 5, 4, 2, 2, 2, 2, 2, 2, 2, 4+aesthetasc, 2, 2, 4, 4+aesthetasc, and 9+aesthetasc; all setae naked; aesthetascs small, setiform.Antenna (Fig. 15F) with short unarmed coxa; basis with 1 inner seta plus 2 exopodal setae (1 minute): endopod 3-segmented with armature formula 1, 4, and 6 plus claw; terminal segment about 3 times longer than wide; curved terminal claw slender; outer margin of endopodal segments ornamented with spinules; distal seta on second segment with blunt tip.

FIG. 15. Archinotodelphys bimerus sp. nov. paratype male. A, habitus, dorsal; B, urosome, ventral; C, left caudal ramus, ventral; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule. Scale bars: A, 0.1 mm; B, E, 0.05 mm; C, D, F–I, 0.02 mm.

FIG. 16. Archinotodelphys bimerus sp. nov. paratype male. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 4; F, right legs 5 and 6, ventral. Scale bars: 0.02 mm.

Labrum (Fig. 15G) with semicircular posteromedian lobe ornamented with long setules and row of spinules on both sides posteriorly. Mandible (Fig. 15H) with about 9 acute teeth of irregular sizes and 2 setae on cutting edge of coxal gnathobase; basis with 1 seta on medial margin; exopod 4-segmented, with 1, 1, 1, and 2 setae on first to fourth segments, respectively, distalmost seta small, less than half length of other 4 setae; endopod 2-segmented with 4 setae on first segment and 9 setae on second. Maxillule (Fig. 15I) with 11 setae on precoxal arthrite; coxa with 1 seta on endite and 2 setae on epipodite; basis with 5 setae on medial margin (grouped 3 and 2); exopod with 4 large setae distally; endopod incompletely 2-segmented with 4 setae (only 3 setae on other member of leg pair) on first segment and 4 setae on second. Maxilla (Fig. 16A) 6-segmented with suture line between precoxa and coxa; precoxa with 3 setae plus 1 spine on proximal endite and 1 seta on distal endite; coxa with 3 setae each on proximal and distal endites; basis with strong claw ornamented with spinules along concave margin, plus 2 setae; endopod 3- segmented, with 2, 2, and 3 setae respectively on first to third segments; setae on second and third segments naked. Maxilliped (Fig. 16B) 4-segmented with 6, 2, 3, and 3 setae on first to fourth segments; terminal segment small; setae on first segment (syncoxa) grouped as 1, 3, and 2.

Legs 1–4 with 3-segmented rami; with same armature formula as preceding species. Inner distal spine on basis of leg 1 and outer setae on exopod of legs 1–4 with membranous fringe bilaterally (Fig. 16C–E).

Leg 5 (Fig. 16F) protopodal segment wider than long, with 1 naked seta; exopodal segment about 1.1 times longer than wide (20×18 μm), with 4 setae; 2 outer distal setae short, spiniform. Leg 6 (Fig. 16F) represented by 2 setae and 1 small, spiniform seta on genital operculum.

Female. Unknown.

Remarks. This new species is established from the male only, but given that archinotodelphyid species typically show sexual dimorphism only in the urosome, the antennule, and legs 5 and 6, it is still possible to make sufficient comparisons. The new species, A. bimerus sp. nov., has an incompletely 2-segmented endopod on the maxillule and each segment is armed with 4 setae. This is a unique character state within the family. The presence of 2, 2, and 3 setae on the first to third endopodal segments of the maxilla is shared only by two species, A. profundus and A. curtus sp. nov. The new species also shares the presence of 5 setae on the basis of the maxillule with A. profundus , but not with A. curtus sp. nov., which carries 7 setal elements on the basis. The new species can be distinguished from A. profundus by the presence of only 9 setae on the distal segment of the mandibular endopod, compared to 8 in A. profundus . In addition, the endopod of the maxillule of A. profundus is unsegmented whereas it is incompletely 2-segmented in A. bimerus sp. nov. These differences serve to distinguish A. bimerus sp. nov. from its congeners.