Onychopontia nichollsi, Sak & Huys & Karaytuğ, 2008

Sak, Serdar, Huys, Rony & Karaytuğ, Süphan, 2008, Disentangling the subgeneric division of Arenopontia Kunz, 1937: resurrection of Psammoleptastacus Pennak, 1942, re-examination of Neoleptastacus spinicaudatus Nicholls, 1945, and proposal of two new genera and a new generic classification (Copepoda, Harpacticoida, Arenopontiidae), Zoological Journal of the Linnean Society 152, pp. 409-458 : 449-455

ONYCHOPONTIA NICHOLLSI SP. NOV.

Type locality: Australia, Western Australia, ‘ Back Beach’ at Dongarra ; washed from sand taken from below 15 cm of the surface .

Material examined: Type material found among syntype series of N. spinicaudatus (see above). Holotype ♀: dissected on six slides ( NHM reg. no. 1994.4807) . Paratypes: eight ♀♀ and one ♂ in alcohol ( NHM reg. nos 1994.4808–4816; antennule of ♂ paratype mounted on separate slide). Collected by A.G. Nicholls on 25–26 March 1940 .

Description

Female: Total body length from tip of rostrum to posterior margin of caudal rami: 210–245 M m (mean = 225 M m, N = 9). Body: slender and cylindrical, without clear distinction between prosome and urosome ( Fig. 21A, B). Hyaline frills of thoracic somites weakly developed and crenulated; those of genital double-somite and free abdominal somites strongly developed, and consisting of narrow, rectangular digitate lappets ( Fig. 21A–D). Genital doublesomite ( Fig. 21A–C): as long as wide; without chitinous ribs marking original segmentation; with one middorsal, two lateral, and two ventral pores. Anal somite ( Fig. 21A, B, D): with two dorsal and two lateral pores. Anal operculum: naked. Anus positioned subterminally between caudal rami.

Caudal rami ( Figs 21D, E, 22F): approximately 2.3 times longer than wide (measured in dorsal view), tapering posteriorly; with a pore dorsally ( Fig. 22F) and two pores laterally ( Fig. 21E); outer distal corner produced into posteriorly directed recurved spinous process, accompanied by outer spinular row at base ( Fig. 21E); dorsal surface without process or spinular row near inner margin. Armature consisting of seven setae: seta I, small; setae II and III, long and naked; seta IV, short, sparsely pinnate, located between seta V and spinous process, and fused basally to seta V; seta V, long, sparsely plumose, and with fracture plane; seta VI, small, naked, and located at inner distal corner; seta VII, foliaceous and triarticulate at base.

Rostrum ( Fig. 21A): small, broadly subtriangular, tapering distally, with two delicate sensillae.

Antennule ( Fig. 22A): long, six-segmented. Segment 1: with a tiny seta near the anterodistal margin. Segment 2: longest, about 2.8 times longer than wide. Segment 4: with long aesthetasc (22- M m long) fused at base with seta. Distal segment: with seven naked setae (one of which spatulate), and apical acrothek consisting of short aesthetasc (13- M m long) and two slender setae. Armature formula: 1-[1], 2-[6 + 1 plumose], 3-[4], 4-[(1 + ae)], 5-[1], 6-[7 + acrothek].

Antenna ( Fig. 22B): coxa small, without ornamentation. Allobasis: about 2.4 times as long as maximum width; original segmentation marked by partial transverse surface suture; without spinular ornamentation. Exopod: one-segmented, elongate, with a naked apical seta (slightly longer than exopod). Free endopod with two spinular rows on anterior surface; lateral armature consisting of two short spines; apical armature consisting of two spines and three geniculate setae, strongest of which with spinules around geniculation and fused basally to tiny accessory seta.

Mandibular palp: two-segmented ( Fig. 22C, D); basis elongate with one lateral seta; endopod with one inner, one outer, and three apical setae (two fused at base); all armature elements naked. Gnathobase: with few sharp teeth distally and one naked seta at dorsal corner.

Maxillule and maxilla: as in O. peteraxi .

Maxilliped ( Fig. 22E): syncoxa, small and unarmed. Basis: elongate and unarmed. Endopod: with small accessory seta and slightly curved claw bearing subterminal spinule.

P1 ( Fig. 23A): intercoxal sclerite, long and narrow. Praecoxa: triangular and naked. Coxa: without ornamentation. Basis: with spinular row near base of endopod; anterior surface with a small inner seta. Exopod: three-segmented, condensed; exp-1 and exp-2 with spinules around outer margin; exp-1 longest, with strong, naked outer spine; exp-2 without outer element; exp-3 with two naked setae, one short, and one long geniculate seta. Endopod: two-segmented, longer than exopod, not prehensile; enp-1 2.2 times longer than wide, with a short serrate inner seta at about halfway along the segment length, and with few spinules along outer margin; enp-2 longer than wide, with a short outer and a long inner geniculate seta.

P2–P4 ( Fig. 23B–D): intercoxal sclerites naked. Praecoxae: small and naked. Coxae: without ornamentation. Bases: generally smaller than coxae, with a spinular row near the base of the endopod and with few spinules along the outer margin; anterior surface with a pore in P4; outer basal seta absent (P2), plumose (P3), or naked (P4). Exopods: three-segmented; segments with spinular ornamentation, as illustrated; inner distal seta of exp-3 sparsely bipinnate, all other elements unipinnate; P3–P4 exp-3 with anterior pore. Endopods: twosegmented, enp-2 very small; P2–P4 enp-1 about 3.5, 3.4, and 3.8 times longer than their respective distal segments, with few spinules along outer margin, as illustrated. P2 enp-2: without inner seta. P2–P3 enp-2: with a sparsely bipinnate apical seta. P4 enp-2: with large, apically serrate seta, fused at base, and minute seta at outer distal corner. Spine and seta formula as follows:

Exopod Endopod P2 0.0.021 0.010

P3 0.0.021 0.010

P4 0.0.021 0.020

Fifth legs ( Figs 21C, 23E): closely set together, but not touching in ventral midline. Baseoendopod and exopod: fused, forming a squarish plate; anterior surface with two pores; distal margin with two pinnate setae (inner one twice the length of the outer one) and long, naked outer seta; outer basal seta, long and plumose.

Genital field positioned near anterior margin of genital double-somite ( Fig. 21C). Genital apertures fused, forming median common slit; closed off by fused P6 forming operculum, with two minute spinous processes on either side; copulatory pore located midventrally, close to genital slit, and flanked by paired secretory pores; seminal receptacles difficult to discern.

Male: Total body length from tip of rostrum to posterior margin of caudal rami: 295 M m. Body ornamentation ( Fig. 24A, B): essentially as in female. Sexual dimorphism: in antennule, genital segmentation, P3 endopod, P5, and P6. Spermatophore length: approximately 18 M m.

KEY TO SPECIES Although some variability has been noted for O. peteraxi , we consider 0.020 and 0.010 as the normal formulae for P2–P3 endopods, respectively (as found in the Chilean population; Mielke, 1987). 1. P4 enp-2: with two well-developed setae ............................................................................................... 2.

P4 enp-2: with vestigial outer seta.......................................................................................................3. 2. P2 enp-2: with inner spine over twice the length of the outer spine; P 5 female with five setae ...... O. intermedia .

P2 enp-2: with both elements equally long; P 5 female with four setae ......................................... O. orientalis . 3. P 5 male: with innermost element setiform and defined at base................................................... O. peteraxi . *

P 5 male: with innermost element spiniform and fused to segment ................................. O. nichollsi sp. nov. *