Archinotodelphys hexasetosus, 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 : 14-17

Archinotodelphys hexasetosus sp. nov.

(Figs. 5, 6)

Type material. Holotype ♀ (MNHN-IU-2014-21194; dissected and mounted on a slide).

Type host. Molgula platybranchia Monniot C., 1970 (MNHN-IT-2008-5713 = MNHN S3 /MOL.A/290) .

Type locality. Banc Seine, N.E. Atlantic Seamount I cruise, Stn DE80 (33°48.5´N, 14°22.6´W), depth 250–256 m; coll. P. Bouchet; 10 October 1987.

Etymology. The name of the species refers to the presence of 6 setae on both the first endopodal segment of the mandible and the exopodal segment of leg 5.

Female. Body (Fig. 5A) rather slender, 1.34 mm long; prosome 659 μm long and gradually narrowing posteri- orly; cephalosome 350×490 μm, with characteristic acutely-produced posterolateral corners on dorsal cephalosomal shield. Urosome (Fig. 5B) 5-segmented: fifth pedigerous somite 168 μm wide. Genital double-somite 200×173 μm, gradually narrowing posteriorly and bearing paired genital apertures dorsolaterally at about 32% of double-somite length. Three free abdominal somites 94×121, 79×115, and 82×116 μm, respectively. Caudal rami widely separated from each other, directed posteriorly; each ramus (Fig. 5C) about 3.3 times as long as wide (136×41 μm): armed with 6 setae; outer lateral seta naked and located about at middle of ramus; other 5 setae plumose.

Rostrum (Fig. 5D) slightly longer than wide, 98×89 μm, tapering towards blunt apex. Antennule (Fig. 5E) 462 μm long and 17-segmented; first segment with 3 setae; setation of other segments uncertain (due to loss of setae during capture and subsequent handling). Antenna (Fig. 5F) with short coxa; basis with 2 plumose setae at outer distal corner, representing exopod; but inner distal seta absent; first to third endopodal segments with 1, 4 (3 distal and 1 at mid-length), and claw plus 6 setae, respectively; third segment about 2.6 times longer than wide (61×23 μm); terminal curved claw small, about half length of segment.

Labrum (Fig. 5G) as figured. Mandible (Fig. 5H) with 8 teeth (3 spinule-like) plus 2 slender setae on coxal gnathobase; basis with subdistal seta on medial margin; exopod 4-segmented with 5 setae (setal formula 1, 1, 1, 2); endopod with 6 naked setae on first segment and 9 setae on second. Paragnath (Fig. 5I) ornamented with 2 denticles apically and setules on medial surface. Maxillule (Fig. 5J) with 10 setae on precoxal arthrite, 1 seta on coxal endite, 2 equal setae on coxal epipodite, 8 setae (3 proximal and 5 distal) on medial margin of basis, 4 distal setae on exopod and 10 setae on endopod. Maxilla (Fig. 6A) 5-segmented with distinct suture between precoxa and coxa; precoxa with 1 spine and 3 setae on proximal endite and 1 seta on distal endite; coxa with 3 setae each on proximal and distal FIG. 5. Archinotodelphys hexasetosus sp. nov. holotype female. A, habitus, dorsal; B, urosome, dorsal; C, left caudal ramus, dorsal; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, paragnath; J, maxillule. Scale bars: A, 0.2 mm; B, 0.1 mm; C–H, J, 0.05 mm; I, 0.02 mm.

FIG. 6. Archinotodelphys hexasetosus sp. nov. holotype female. A, maxilla; B, basis and endopod of maxilla; C, maxilliped; D, leg 1; E, leg 2; F, leg 4; G, leg 5. Scale bars: 0.05 mm.

endites, middle seta on distal endite spiniform, ornamented with fine spinules along distal margin and scattered setules along proximal margin: basis with large claw plus 2 setae (Fig. 6B): endopod 2-segmented, armed with 2 setae on first segment and 6 setae on second. Maxilliped (Fig. 6C) 4-segmented with 5, 2, 3, and 4 setae respectively on first to fourth segments.

Legs 1–4 with 3-segmented rami: armature formula as in preceding species. Outer seta on basis of legs naked and relatively large (Fig. 6D–F). Spines on exopod of leg 1 each with flagellate tip. Distal spine on outer margin of third exopodal segment of leg 4 much longer than proximal.

Leg 5 (Fig. 6G) well-demarcated from somite; protopodal segment 53×52 μm and armed with 1 seta on outer margin; exopodal segment about 3.8 times longer than wide (92×25 μm) and bearing 6 setae (1 outer, 3 distal, and 2 inner). Leg 6 represented by 1 seta and 1 spine in genital aperture.

Male. Unknown.

Remarks. The possession of 6 setae on the free exopodal segment of leg 5 is shared only with A. polynesiensis and the newly established A. momus sp. nov.; the females of all other species including all the new species described below possess only 4 setae on this segment. The elongation of the exopodal segment of leg 5 in A. hexasetosus sp. nov. is also remarkable: in all other species this segment has a L:W ratio in the range of 1.1:1 to 3.0:1 whereas in the new species the segment is 3.8 times longer than wide. The new species possesses an inner coxal seta on leg 4, as in A. momus sp. nov. whereas A. polynesiensis lacks this seta ( Monniot, 1986).

The first endopodal segment of the mandible has 6 setae, as in typical A. polynesiensis , A. curtus sp. nov., A. illgi sp. nov. and A. momus sp. nov. However, the first three of these species each has 10 setae on the second endopodal segment and A. momus sp. nov. has only 8 setae: in contrast, the new species has 9 setae. Archinotodelphys hexasetosus sp. nov. has a 2-segmented endopod on the maxilla and these segments carry 2 and 6 setae, respectively, from which we infer that the distal segment is a compound segment derived from fusion of the second and third segments expressed in other species. The maxillary endopod is 3-segmented in all other species except for A. antarcticus sp. nov. described below, which has a setation pattern of 1, 5. [There is some uncertainty concerning the maxilla of A. typicus which Lang (1949) shows as 2-segmented and bearing only 4 elements: but it is probable that setal elements are missing.] Finally, the setal formula 5, 2, 3, and 4 of the 4-segmented maxilliped is unique within the genus: all other species which retain separate first and second endopodal segments on the maxilliped carry a maximum of 3 setae on the second endopodal segment. These differences provide sufficient evidence to support the establishment of a new species to accommodate this material.