Archinotodelphys rostralis, 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 : 41-44

Archinotodelphys rostralis sp. nov.

(Figs. 24, 25)

Type material. Holotype (♀, MNHN-IU-2014-21205, dissected and mounted on a slide), in Polycarpa nigricans Heller, 1878 , Thio , New Caledonia; paratype (♂, MNHN-IU-2014-21206 intact), in P. nigricans, Uie Bay, Canal Woodin , New Caledonia, Stn NC 36, depth 18m, Monniot coll., 11 March 1987.

Etymology. The name of the new species refers to the prominent, anteriorly-directed rostrum of this species.

Female. Body (Fig. 24A) slender; length 2.47 mm; prosome 1.14 mm long; greatest width 596 μm across cephalosome. First pedigerous somite only slightly narrower than second pedigerous somite. Urosome (Fig. 24B) 5-segmented; fifth pedigerous somite 286 μm wide. Genital double-somite 332×228 μm; slightly expanded later- ally in anterior quarter; paired genital apertures located dorsolaterally at 27% of double-somite length. Three free abdominal somites 232×170, 173×145, and 164×136 μm, respectively. Caudal ramus (Fig. 24B), about 5.4 times longer than wide (273×51 μm) and armed with 6 setae; all setae naked and shorter than ramus; lateral seta located at 32% of ramus length.

Rostrum (Fig. 24A, C, D) large (about 200×70 μm), anteriorly-directed, with parallel lateral margins in proximal two-thirds and tapering in distal third to pointed apex visible in dorsal view (Fig. 24D), apex blunt in lateral view (Fig. 24C). Antennule (Fig. 24E) 390 μm long and 15-segmented; armature formula 3, 5, 8, 2, 2, 6, 4+aesthetasc, 1, 2, 1, 2, 2+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc; all setae naked except 1 on first segment. Antenna (Fig. 24F) with unarmed coxa; basis with 1 pinnate and 1 tiny exopodal setae at outer distal corner; endopod 3-segmented with armature formula 1, 4, and 6+claw; terminal claw large and strongly curved.

Labrum (Fig. 24G) simple (without posteromedian lobe), ornamented with few spinules and setules at each posterolateral corner. Mandible (Fig. 24H) with 4 teeth and 1 seta on coxal gnathobase; proximalmost tooth with bifid tip; basis with 1 seta on medial margin: exopod 4-segmented with 1 seta on each segment; endopod 2-segmented with 4 and 9 setae on first and second segments, respectively. Maxillule (Fig. 24I) with 9 setae on precoxal arthrite; coxa with 1 seta on endite and 2 unequal setae on epipodite; basis with 4 (1+3) setae on medial margin; exopod with 4 setae apically; endopod 1-segmented with 8 setae (4 medial and 4 distal); all setae naked except weakly pinnate outermost distal seta. Paragnath (Fig. 25A) ornamented with 3 teeth at mediodistal region and setules on medial margin. Maxilla (Fig. 25B) 5-segmented; syncoxa with 4, 1, 2, and 3 setae on each of first to fourth endites, respectively; one of setae on first and fourth endites small; basis with 1 seta and strong claw bearing spinules along concave margin; endopod 3-segmented, bearing 1, 1, and 4 setae on first to third segments, respectively. Maxilliped 3-segmented with 5, 1, and 4 setae on first to third segments, respectively (Fig. 25C); setae on first segment grouped as 1, 2, and 2.

Legs 1–4 biramous with 3-segmented rami: armature formula for legs 1–4 as in generic diagnosis. Outer seta on basis of legs 1-4 naked (Fig. 25D–F). Inner distal spine on basis of leg 1 smooth and shorter than first endopodal segment. All outer spines on exopods smooth.

FIG. 24. Archinotodelphys rostralis sp. nov. holotype female. A, habitus, dorsal; B, urosome, dorsal; C, rostrum, lateral view from left side; D, rostrum, ventral; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule. Scale bars: A, 0.5 mm; B, 0.1 mm; C–F, H, I, 0.05 mm; G, 0.02 mm.

FIG. 25. Archinotodelphys rostralis sp. nov. holotype female. A, paragnath; B, maxilla; C, maxilliped; D, leg 1; E, leg 2; F, leg 4; G, leg 5. Scale bars: A, 0.02 mm; B–G, 0.05 mm.

Leg 5 (Fig. 25G) protopodal segment wider than long, armed with 1 outer seta and ornamented with several inner spinules; exopodal segment rounded, bulbous, about 1.7 times longer than wide (176×104 μm), widest at 60% of length; smallest second inner seta orientated close to inner margin. Leg 6 represented by 1 spine and 1 seta.

Male. (observed undissected). Body similar to that of female. Length 1.67 mm. urosome 6-segmented. Caudal ramus 207×34 μm, about 6.1 times longer than wide.

Rostrum as in female. Antennule 13-segmented, geniculate between eleventh and twelfth segments. Antenna, labrum, mandible, maxilla, and maxilliped as in female. Maxillule with 5 (1+4) setae on basis.

Legs 1–4 as in female. Leg 5 similar to that of female, with 4 setae, but dimensions not measured. Leg 6 represented by 2 setae and 1 spinule on genital operculum.

Remarks. This new species is similar to A. elegans sp. nov. in having reduced setation of the mandible, the maxilla and the maxilliped. The main differences are the much more elongate caudal rami in A. rostralis sp. nov. with a L/W ratio 5.4:1 (compared to 3.6: 1 in A. elegans sp. nov.), the possession of 4 (not 6) setae on the basis of the maxillule, and the shape of the rostrum and the exopod of leg 5. The elongate rostrum of A. rostralis sp. nov. is unique: it is directed frontally so almost its entire length is visible in dorsal view (Fig. 24A) and its apex tapers to a point in dorsal view (Fig. 24D) but is bluntly rounded in lateral view (Fig. 24C). In A. elegans sp. nov. the rostrum is also elongate and has a similar general shape but it is directed antero-ventrally so that it is only just visible in dorsal view (cf. Fig. 22A). The rounded shape of the free exopodal segment of leg 5 is less pronounced in A. rostralis sp. nov. than in A. elegans sp. nov., and the L/W ratio is 1.7:1 compared to 1.3: 1 in the latter. This combination of features serves to distinguish between these two new species.