Archinotodelphys curtus, 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 : 8-11

Archinotodelphys curtus sp. nov.

(Figs. 1, 2)

Type material. Holotype ♀ (MNHN-IU-2014-21192; dissected and mounted on a slide).

Type host. Styela sp.

Type locality. Indian Ocean, Safari II cruise of R. V. Marion Dufresne ( MD 28), Stn data unknown; 24 July – 24 August 1981.

Etymology. The name curtus refers to the relatively short caudal rami of this species.

Female. Body cyclopiform (Fig. 1A) dorsoventrally flattened; 1.52 mm total length; prosome length 836 μm, greatest width 636 μm. Cephalosome 436 μm long; first pedigerous somite 564 μm wide, distinctly narrower than cephalosome. Urosome (Fig. 1B) 5-segmented; fifth pedigerous somite 203 μm wide. Genital double-somite 227×189 μm, 1.2 times as long as wide, narrowing slightly posteriorly; paired genital apertures located near anterior third. Three free abdominal somites 85×133, 61×127, and 88×121 μm, respectively. Caudal rami widely separated at base, divergent; each ramus about 2.3 times longer than wide (115×50 μm), armed with 6 naked setae; outer lateral seta located at about 45% of ramus length (Fig. 1C).

Rostrum (Fig. 1D) 122×96 μm, tapering to bluntly pointed tip. Antennule 453 μm long and 17-segmented; ar- mature formula 3, 6, 8, 2, 2, 6, 4+aesthetasc, 2, 2, 2, 2, 2+aesthetasc, 0, 1, 2, 2+aesthetasc, and 7+aesthetasc; seventh segment with incomplete suture line on one side; all setae thin and naked. Antenna (Fig. 1F) with short, unarmed coxa: basis with pinnate inner seta, and 2 unequal (1 larger plumose and 1 small naked) outer setae representing exopod: endopod 3-segmented; first segment with 1 small seta on middle of inner margin; second segment with 4 setae (3 at inner distal corner and 1 on inner margin); third segment 47×27 μm, as long as second, armed with 1 slender curved claw and 6 naked setae distally.

Labrum not observed (destroyed during dissection). Mandible (Fig. 1G) with 8 spiniform teeth (including smaller second distal most one), 2 proximal setae, and row of fine spinules on medial margin of gnathobase; basis with 1 plumose seta on medial margin; exopod 4-segmented with 5 setae (1, 1, 1, and 2 on first to fourth segments respectively), 2 terminal setae plumose; endopod with 6 and 10 naked setae on first and second segments, respectively. Maxillule (Fig. 1H) with 11 setae on arthrite, 1 seta on coxal endite, and 2 setae on epipodite; basis with 1 spine and 6 setae on inner margin; endopod unsegmented with 11 setae, outer distalmost seta plumose, other 10 naked; exopod with 4 large, plumose setae. Maxilla (Fig. 2A) consisting of precoxa, coxa, basis, and 3-segmented endopod: complete suture line separating precoxa and coxa; precoxa with 4 (1 of them small) and 1 setae on proximal and distal endites, respectively; coxa with 3 setae each on proximal and distal endites; basis with 2 setae and 1 strong claw bearing fine spinules along proximal margin; endopod short, 3-segmented and armed with 2, 2, and 3 FIG. 1. Archinotodelphys curtus sp. nov. holotype female. A, habitus, dorsal; B, urosome, dorsal; C, left caudal ramus, dorsal; D, rostrum; E, antennule; F, antenna; G, mandible; H, maxillule. Scale bars: A, 0.2 mm; B, 0.1 mm; C–H, 0.05 mm.

FIG. 2. Archinotodelphys curtus sp. nov. holotype female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 4; F, leg 5; G, leg 6, dorsolateral. Scale bars: A–F, 0.05 mm; G, 0.02 mm.

setae on first to third segments, respectively. Maxilliped (Fig. 2B) 4-segmented, syncoxa with 6 setae (4 proximal and 2 distal), basis with 2, and 2-segmented endopod with 4, and 3 setae respectively; second seta (indicated by arrowhead in Fig. 2B) missing on one member of limb pair.

Legs 1–4 with 3-segmented rami; outer margins of exopods smooth (Fig. 2C–E). Leg 1 basis with inner distal spine 59 μm long, naked and slightly curved. Leg 3 same as leg 2 (Fig 2D) in structure. Armature formula of legs 1–4 as in family diagnosis.

Leg 5 (Fig. 2F) consisting of protopodal and exopodal segments; protopodal segment wider than long and distinctly articulated from somite, with 1 seta on outer margin; exopodal segment about 2.3 times as long as wide (124×55 μm), with 4 setae (1 lateral and 3 distal); outer distal seta much longer than other 3; inner distal seta weakly plumose. Leg 6 (Fig. 2G) represented by 1 seta, 1 spine and 1 spiniform process located in genital aperture.

Male. Unknown.

Remarks. This new species is similar to typical A. polynesiensis and A. momus sp. nov. in having 6 setae on the first endopodal segment of the mandible and 11 setae on the endopod of the maxillule, but it differs in having 7 setae on the basis of the maxillule (cf. 8 in A. polynesiensis ) and only 4 setae on the exopod of leg 5 (cf. 6 in A. polynesiensis and A. momus sp. nov.). These differences are sufficient to justify the establishment of a new species.

A unique feature of the new species is the presence of 4 setae on the proximal segment of a 2-segmented endopod on the maxilliped. However, this fourth seta was present on one member of the limb pair only; it was absent on the other. In all other species, including the new species described here, a maximum of 3 setae is present on this segment.