Archinotodelphys illgi, 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 : 11-14

Archinotodelphys illgi sp. nov.

(Figs. 3, 4)

Type material. Holotype ♀ (MNHN-IU-2014-21193; dissected and mounted on a slide).

Type host. unknown

Type locality. unknown

Etymology. The species is named in honour of Paul L. Illg, who contributed much to our understanding of associated copepods in general and the Archinotodelphyidae in particular.

Female. Body (Fig. 3A) dorsoventrally flattened; body length 1.43 mm, prosome length 836 μm; cephalosome 412×570 μm. First pedigerous somite 133×418 μm, distinctly narrower than second. Urosome (Fig. 3B) 5-seg- mented; fifth pedigerous somite 185 μm wide. Genital double-somite 167×170 μm, gradually narrowing posteriorly; paired genital apertures located dorsolaterally at about 37% of length along double-somite. Three free abdominal somites 64×130, 51×127, and 87×124 μm, respectively. Anal somite (Fig. 3C) ornamented on ventral surface with 2 transverse rows of fine spinules proximally plus row of fine spinules along posterior margin near origin of caudal rami. Caudal ramus (Fig. 3C) about 4 times longer than wide (158×40 μm), armed with 6 naked setae; outer lateral seta located at 43% of length of caudal ramus.

Rostrum (Fig. 3D) longer than wide with rounded apex. Antennule (Fig. 3E) 472 μm long and 17-segmented; armature formula 3, 5, 8, 2, 2, 6, 4+aesthetasc, 2, 2, 2, 2, 2, 1, 1, 2, 2+aesthetasc, and 7+aesthetasc; all setae thin and naked. Antenna (Fig. 3F) with short, unarmed coxa: basis with inner distal seta and 2 outer setae (1 large plumose and 1 small naked) representing exopod: endopod 3-segmented with 1 seta on inner margin of first segment, 5 setae (4 at inner distal corner and 1 on inner margin) on second segment, and 1 small curved claw plus 6 setae on third.

Labrum (Fig. 3G) narrowing distally, with large mid-posterior lobe; ornamented with long setules on posterolateral corners and along free margin of mid-posterior lobe. Mandible (Fig. 3H) with 2 setae and 8 teeth on gnathobase; proximal, second and third teeth tipped with spinules; basis with 1 seta on inner margin; exopod 4-segmented with setal formula 1, 1, 1, and 2 plumose setae; endopod 2-segmented, bearing 6 and 10 setae on first and second segments, respectively. Paragnath (Fig. 3I) lobate, ornamented with setules on inner surface. Maxillule (Fig. 4A) with 11 setae on arthrite (1 on ventral surface), 1 seta on coxal endite, 2 setae on epipodite, 7 setae (one spiniform) on medial margin of basis, 4 setae on exopod and 10 setae on endopod. Maxilla (Fig. 4B) with distinct suture line between precoxa and coxa; precoxa with 3 setae plus spiniform process on proximal endite and 1 seta on distal endite; coxa with 3 setae each on proximal and distal endites; basis with claw ornamented with spinules along proximal margin and bearing 2 setae; endopod short and 3-segmented, armed with 2, 2, and 4 setae on first to third segments, FIG. 3. Archinotodelphys illgi sp. nov. holotype female. A, habitus, dorsal; B, urosome, dorsal, C, anal somite and left caudal ramus, ventral; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, paragnath. Scale bars: A, 0.2 mm; B, 0.1 mm; C–I, 0.05 mm.

FIG. 4. Archinotodelphys illgi sp. nov. holotype female. A, maxillule; B, maxilla; C, maxilliped; D, leg 1; E, leg 2; F, leg 4; G, right genital aperture, dorsal. Scale bars: A–F, 0.05 mm; G, 0.02 mm.

respectively. Maxilliped (Fig. 4C) 4-segmented, fourth segment small: setal armature comprising 6, 2, 3, and 3 setae on first to fourth segments.

Legs 1–4 with 3-segmented rami: armature formula as in preceding species. Outer seta of basis naked in legs 1–3 but plumose in leg 4 (Figs. 4D–F). Inner distal spine on basis of leg 1 extending to distal margin of second endopodal segment, 54 μm long, and spinulose on both margins.

Leg 5 (Fig. 3B) 2-segmented: protopodal segment distinctly articulated from somite, 62×78 μm, bearing outer naked seta; exopodal segment 2.07 times longer than wide (93×45 μm), armed with 4 thin naked setae, mid-terminal seta smallest; medial seta largest at 255 μm, extending to posterior margin of anal somite. Leg 6 (Fig. 4G) repre- sented by 1 naked seta and 1 spine located in genital aperture.

Male. Unknown.

Remarks. This new species can readily be distinguished from A. polynesiensis and A. momus sp. nov. by the presence of only 4 setae on the exopodal segment of leg 5. Both of these other species carry 6 setae on the exopodal segment of leg 5. The existing species A. typicus , A. gurneyi , A. phallusiae , and A. profundus all share the possession of 4 setae on the free exopodal segment of leg 5, but all of them carry only 4 setae on the first endopodal segment of the mandible. The new species, A. illgi sp. nov., and A. curtus sp. nov. both have 6 setae on this segment. In A. illgi sp. nov. the endopod of the maxilla is armed with a total of 8 setae (arranged 2, 2, and 4 on the first to third segments, respectively). No other existing species has 8 setae on the endopod of the maxilla: in A. polynesiensis it has 7 setae (arranged 2, 1, and 4), and A. profundus also has 7 setae (arranged 2, 2 and 3). Archinotodelphys curtus sp. nov. also has 7 setae arranged 2, 2 and 3, but the second endopodal segment of its antenna is armed with 5 setae (4 distal plus 1 medial) in A. illgi sp. nov. whereas in A. curtus sp. nov. this segment carries only 4 setae (3 distal and 1 medial). These differences serve to justify the establishment of A. illgi as a new species.