Archinotodelphys elegans, 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 : 38-41

Archinotodelphys elegans sp. nov.

(Figs. 22, 23)

Type material. Holotype (intact ♀, MNHN-IU-2014-21203) 1 paratype (intact ♀, MNHN-IU-2014-21204), 1 dis- sected ♀ paratype in the collection of IHK.

Type host. Polycarpa argentata (Sluiter, 1890) (MNHN-IT-2008-6326 = MNHN S1 POL.B 360) .

Type locality. Ngeteklou Island , Koror, Palau Islands (07°19.47’N, 134°29.42’E), depth 10 m, OCDN 3413 - T, 01, CRRFcoll., November 1995 .

Etymology. The name of the new species, elegans , refers to the very slender form of the body.

Female. Body (Fig. 22A, B) slender, 1.82 mm long; prosome 910 μm long, with sub-parallel lateral margins; greatest width 467 μm across cephalosome. Urosome 5-segmented; fifth pedigerous somite 245 μm wide; genital double-somite 267×176 μm; bearing paired genital apertures dorsally at anterior third of double-somite (Fig. 22C). Three free abdominal somites 170×158, 136×133, and 143×127 μm, respectively. Caudal ramus (Fig. 22D) about 3.6 times as long as wide (155×43 μm); armed with 6 naked setae, outer lateral seta located at about 40% of ramus length; dorsal seta (seta VII) located at 74% of ramus length; lengths of mid-terminal setae 352 (inner) and 284 (outer) μm.

Rostrum (Fig. 22E) elongate (130×55 μm), tapering weakly towards blunt tip. Antennule (Fig. 22F) 310 μm long and 15-segmented; armature 3, 5, 7, 2, 2, 6, 4+aesthetasc, 1, 2, 1, 2, 2+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc; seventh segment subdivided on ventral surface; one seta on first segment pinnate, other setae naked. Antenna (Fig. 22G) with unarmed coxa; basis with 1 large and 1 tiny exopodal setae at outer distal corner, lacking seta at inner distal corner; endopod 3-segmented with armature formula 1, 4, and 6 plus claw; third endopodal segment (32×27 μm), shorter than second; 1 seta on second segment and 3 on third bluntly tipped.

Labrum (Fig. 22H) with rounded, projecting posterolateral corners ornamented with spinules and setules; posteromedian lobe smooth, not projecting beyond posterior margin of labrum. Mandible (Fig. 22I) with 4 teeth and 1 seta on coxal gnathobase; basis with 1 seta on medial margin; exopod 4-segmented, with 1 seta on each segment (4 setae in total); endopod with 4 and 9 setae on first and second segments, respectively. Paragnath (Fig. 22J) ornamented with 2 teeth apically and setules on medial surface. Maxillule (Fig. 23A) with 9 setae on precoxal arthrite, 1 seta on coxal endite and 2 unequal setae on coxal epipodite; basis with 6 setae on medial margin; exopod with 4 setae; endopod unsegmented and bearing 8 setae (4 medial and 4 distal). Maxilla (Fig. 23B) 5-segmented; syncoxa with 4 (including 1 small), 1, 2, and 3 (including 1 small) setae on first to fourth endites, respectively; basis with 1 seta and strong claw bearing spinules along concave margin: endopod 3-segmented with 1, 1, and 4 setae; setae on first and second segments and 1 seta on terminal segment elongate. Maxilliped (Fig. 23C) 3-segmented with 5, 1, and 4 setae on first to third segments, respectively; 5 setae on first segment grouped as 1, 2, and 2, from proximal to distal.

Legs 1–4 biramous with 3-segmented rami; armature formula for legs 1–4 as in previous species. Outer seta on basis of legs 1–4 naked. Inner distal spine on basis of leg 1 (Fig. 23D) stout, shorter than first endopodal segment. Terminal process on third endopodal segment of legs 1–4 produced and sharply pointed (Fig. 23D–F). Terminal spine on third exopodal segment of legs 2–4 setiform.

FIG. 22. Archinotodelphys elegans sp. nov. paratype female. A, habitus, dorsal; B, habitus, lateral view from right side; C, first two urosomites, dorsal; D, anal somite and caudal rami, dorsal; E, rostrum; F, antennule; G, antenna; H, labrum; I, mandible; J, paragnath. Scale bars: A, B, 0.2 mm; C, D, 0.1 mm; E–G, 0.05 mm; H–J, 0.02 mm.

FIG. 23. Archinotodelphys elegans sp. nov. paratype female. A, maxillule; B, maxilla; C, maxilliped; D, leg 1; E, leg 2; F, leg 4; G, leg 5; H, right genital aperture, dorsal. Scale bars: A–C, H, 0.02 mm; D-G, 0.05 mm.

Leg 5 (Fig. 23G) protopodal segment clearly defined from somite, longer than wide, with 1 naked outer dorsal seta and ornamented with several spinules on proximo-medial surface: exopodal segment subovate, about 1.3 times longer than wide (174×130 μm) with concave medial surface; armed with 4 naked setae (1 small distal and 3 on in- ner margin); all setae short, less than half width of exopodal segment. Leg 6 (Fig. 23H) represented by 1 spine and 1 naked seta on genital operculum.

Male. Unknown.

Remarks. This new species differs from all its congeners and from the other new species described above in the possession of a total of only 4 setae on the compound distal segment of its 3-segmented maxilliped. The maxilliped is also 3-segmented in A. gurneyi comb. nov., A. momus sp. nov., and A. reductus sp. nov., but these species have either 6 or 7 setae on the compound distal segment. Similarly, all existing species and all the new species described above have a total of 5 setae on the exopod of the mandible whereas the new species has only 4 setae. The ramus is 4-segmented in all species but the setal formula in A. elegans sp. nov. is 1, 1, 1, 1, compared with 1, 1, 1, 2 found in the majority of all existing species plus all the new species described above (see Table 2). The free exopodal segment of leg 5 is flattened and rounded in A. elegans sp. nov., resulting in a subovate shape. This shape is unique within the family and serves to distinguish A. elegans sp. nov. from all of its congeners. The fifth leg is orientated vertically with its inner margin directed ventrally (Fig. 22C). These differences justify the establishment of a new species.