Archinotodelphys reductus, 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 : 34-38

Archinotodelphys reductus sp. nov.

(Figs. 19–21)

Type material. Holotype (♀, MNHN-IU-2014-21202; dissected and mounted on a slide).

Type host. Pyura gangelion (Savigny, 1816) (MNHN-IT-2008-7540, = MNHN S2 /PUY/143) .

Type locality. Kai Islands , Indonesia, KARUBAR cruise, N/O Baruna Jaya 1, Stn DW 31 (05°40´S, 132°51´E), depth 288 m, Bouchet, Kastoro & Métivier coll., 26 October 1991

Etymology. The name of the new species refers to the extremely reduced setation of the endopod of the maxilla.

Female. Body (Fig. 19A) slender; length 1.59 mm; prosome 788 μm long; greatest width across cephalosome 426 μm. First pedigerous somite not narrow, wider than second somite. Urosome (Fig. 19B) 5-segmented; fifth pedi- gerous somite 178 μm wide; pseudo-somite present between fifth pedigerous and genital double-somites. Genital double-somite 203×151 μm; paired genital apertures located dorsolaterally in anterior quarter of somite. Three free abdominal somites 126×111, 116×97, and 102×89 μm, respectively. Caudal ramus about 6.3 times longer than wide (194×31 μm) and armed with 6 setae; outer lateral seta located at about 40% of ramus length; 2 mid-terminal and dorsal setae naked, other 3 setae pinnate.

Rostrum (Fig. 19C) longer than wide (79×56 μm), tapering towards rounded apex. Antennule (Fig. 19D) 290 μm long and 17-segmented; armature formula 3, 5, 8, 2, 2, 6, 4+aesthetasc, 1, 2, 1, 2, 1+aesthetasc, 0, 1, 2, 2+aesthe- tasc, and 7+aesthetasc; 2 setae on first segment pinnate, other setae naked; aesthetascs thin, setiform. Antenna (Fig. 19E) with short, unarmed coxa: basis with minute seta at inner distal corner, plus 1 large and 1 tiny exopodal setae at outer distal corner, and ornamented with row of several spinules in middle of inner margin: endopod 3-segmented; first segment with 1 seta on inner margin and expanded, spinulose outer margin; second segment with 4 setae distally (1 bluntly tipped) and row of fine spinules on outer margin; third segment about 1.6 times longer than wide; armed with 6 setae (3 bluntly tipped) plus slender curved claw, and ornamented with spinules on outer margin.

FIG. 19. Archinotodelphys reductus sp. nov. holotype female. A, habitus, dorsal; B, urosome, dorsal; C, rostrum; D, antennule; E, antenna; F, maxillule; G, right genital aperture, dorsal. Scale bars: A, 0.2 mm; B, 0.1 mm; C–F, 0.05 mm; G, 0.02 mm, FIG. 20. Archinotodelphys reductus sp. nov. holotype female. A, labrum; B, mandible; C, maxilla; D, maxilliped; E, leg 1; F, leg 2. Scale bars: A, D, 0.02 mm; B, C, E, F, 0.05 mm.

FIG. 21. Archinotodelphys reductus sp. nov. holotype female. A, leg 4; B, leg 5. Scale bars: 0.05 mm.

Labrum (Fig. 20A) with semicircular posteromedian lobe; ornamented with spinules and setules along posterior margin. Mandible (Fig. 20B): medial margin of coxal gnathobase with 4 teeth, 1 seta, and pectinate region, 2 needle-like spinules between second and third teeth, and 1 subsidiary tooth between distal 2 teeth: basis with 1 seta on medial margin: exopod 4-segmented with 1, 1, 1, and 2 setae, all setae equal in length: endopod with 4 and 10 setae on first and second segments, respectively. Maxillule (Fig. 19F) with 9 setae on precoxal arthrite; coxal endite with 1 seta; coxal epipodite with 2 unequal setae; basis with 6 setae on medial margin; exopod with 4 setae; endopod 2-segmented, with 6 and 4 setae on first and second segments. Maxilla (Fig. 20C) 5-segmented; syncoxa with 4 (including 1 small), 1, 2, and 3 setae representing first to fourth endites; basis with 1 seta and 1 strong claw bearing fine spinules along concave margin; endopod 3-segmented with 1, 1, and 3 setae on first to third segments. Maxilliped (Fig. 20D) 3-segmented with 5, 1, and 6 setae on first to third segments; 5 setae on first segment grouped as 1, 2, and 2 from proximal to distal.

Legs 1–4 biramous with 3-segmented rami. Leg 1 (Fig. 20E) with small outer seta on basis; inner distal spine on basis stout, about half as long as first endopodal segment; outer spine on first exopodal segment of legs 1–4 distinctly larger than spines on other exopodal segments. Distal process on third endopodal segment of legs 1–4 well-developed, spiniform (Figs. 20E, F, 21A). Armature formula for legs as for generic diagnosis but with inner and distal margins of third endopodal segment of legs 1-3 indistinctly delimited:

Coxa Basis Exopod Endopod

Leg 1: 0-1 1-I I-1; I-1; III, I, 4 0-1; 0-1; 1, 5

Legs 2 & 3: 0-1 1-0 I-1; I-1; III, 1, 5 0-1; 0-2; 1, 5

Leg 4: 0-1 1-0 I-1; I-1; II, 1, 5 0-1; 0-2; 1, 2, 2

Leg 5 (Fig. 21B) protopodal segment clearly defined from somite, with 1 naked outer seta; exopodal segment, 1.6 times longer than wide (81×50 μm), broadening distally and armed with setae around distal margin, outermost seta naked, other 3 setae pinnate. Leg 6 (Fig. 19G) represented by 1 seta and 1 spine on genital operculum.

Male. Unknown.

Remarks. The distinguishing feature of this species is the reduction in the setation of the endopod of the maxilla: it has an armature formula of 1, 1, and 3 on the first to third segments. This is the most extreme reduction found in any described species, including the additional new species described below. All other species possess a total of between 6 and 8 setae on the maxillary endopod compared to the 5 setae retained in A. reductus sp. nov. (see Table 2). The armature formula of the 3-segmented maxilliped is also unique: the first to third segments carry 5, 1, and 6 setae, respectively. The third exopodal segment of legs 2 and 3 carries 3 spines and 6 setae, and in leg 4 it carries 2 spines and 6 setae. In each of these legs the terminal spine is setiform, but its derivation from the terminal spine is indicated by the plumose ornamentation along the inner margin only.