Onychopontia nichollsi Sak & Huys & Karaytuğ 2008, 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. *