Neoleptastacus supersetosus sp. nov.

(Figs 9–11)

https://zoobank.org/ 316E69F8-8817-4599-9126-F24A67BE3579

Pararenopontia poliseta —nomen nudum by Sak (2004: 273)

Type locality. Kuwait, Shuwaikh (29°21’41.8” N, 47°57’19.2” E) mid- and upper tide levels on public recreational beach within Kuwait Bay adjacent to the commercial port, surrounded by extensive urban development. Relatively steeply sloping sandy beach, bounded to seaward by extensive limestone flats.

Type material. Holotype ♀ (dissected on eight slides) (reg. no NHMUK 2024.1063) . Paratypes are one ♂ (dissected) and one ♀ and one ♂ preserved in alcohol (reg. nos NHMUK 2024.1064–1066). All specimens were collected from the type locality; leg. S. Livesey and N. O’Brien, 3 June 2004 .

Description of female. Total body length from tip of rostrum to posterior margin of caudal rami 225 μm (n = 1). Body (Fig. 9A) slender and cylindrical without clear distinction between prosome and urosome. Hyaline frills of thoracic somites weakly developed and smooth; those of genital double-somite and free abdominal somites strongly developed and consisting of rectangular digitate lappets (Figs 9A; 10A; 11C). Somites connected by well-developed intersomitic membranes. Somites bearing P2–P5, genital double-somite and second abdominal somite with internal semicircular reinforcements forming pattern as figured. Genital double-somite (Figs 9A; 10A) about as long as wide (measured in ventral aspect); with two ventral pores in posterior half (Figs 10A).

Anal somite (Fig. 10A; 11C, D) without paired, dorsally recurved, spinous processes; with two sensilla dorsally and few spinules either side of ventral midline.Anal operculum well developed, semicircular, without ornamentation; covering terminally positioned anal opening. Anal frill triradiate, distinctly incised (giving a spinulose appearance underneath anal operculum).

Caudal rami (Figs 10A; 11C, D) about 2.2 times longer than wide (measured in lateral view from anterior margin to apex of spinous process), distinctly tapering posteriorly with outer margin almost straight and inner margin distinctly convex; outer distal corner produced into short posteriorly directed, dorsally recurved spinous process; with pore ventrally near proximal margin (Fig. 10A) and dorsally at base of spinous process (Fig. 11C); inner margin with conspicuous spinules near base of seta VII (Fig. 11C). Armature consisting of seven setae; seta I small; setae II and III (displaced to dorsal surface) long and naked; seta IV short, naked, located between seta V and posterior spinous process; seta V long, naked, with proximal fracture plane; seta VI small, naked and located at inner distal corner; seta VII distinctly foliaceous and tri-articulate at base.

Rostrum (Fig. 11B) small, broadly subtriangular, tapering distally; apical part lobate and demarcated by bilateral constrictions; with two delicate sensilla.

Antennule (Fig. 11E) moderately long and slender, 6-segmented. Segment 1 with small seta near anterodistal margin. Segment 2 longest, about three times longer than wide. Segment 4 with long aesthetasc (L: 21 μm) fused at base with seta. Distal segment with seven setae (none distinctly spatulate) and apical acrothek consisting of short aesthetasc (L: 12 μm) and two setae. All setal elements naked except for plumose seta on dorsal surface of segment 2. Armature formula: 1-[1], 2-[7 + 1 plumose], 3-[4], 4-[(1 + ae)], 5-[1], 6-[7 + acrothek].

Antenna (Fig. 9B, C). Coxa small, without ornamentation (not figured). Basis and proximal endopodal segment forming incompletely fused allobasis, about 2.5 times as long as maximum width; original basis-endopod boundary marked by short transverse surface suture at level of exopodal articulation and by constriction at abexopodal side; proximal part representing original basis with single spinules at distal corner. Exopod one-segmented, unornamented and elongate, with a naked apical seta (about 1.2 times longer than exopod). Free endopodal segment with few lateral spinules proximally and transverse spinular row distally; medial armature consisting of two short spines (indicated by arrows in Fig. 9B); apical armature consisting of two naked spines and three geniculate setae, longest of which with spinules around geniculation and fused basally to naked accessory seta.

Mandible, maxillule, maxilla and maxilliped as in N. spinicaudatus (see Sak et al. 2008: Figs 16D, E; 17E, F).

P1 (Fig. 9D). Intercoxal sclerite wide and subrectangular. Praecoxa small, triangular and naked. Coxa wider than long, without ornamentation. Basis without spinular ornamentation; anterior surface with small naked seta near medial margin. Exopod two-segmented; segments with several spinules around outer margin; exp-1 unarmed; exp-2 with unipinnate outer spine and two geniculate setae distally. Endopod two-segmented, not prehensile, slightly longer than exopod; enp-1 about 1.4 times longer than enp-2, with a serrate inner seta arising from distal third and four coarse spinules along outer margin; enp-2 without spinules, distal margin with naked outer spine and geniculate inner seta.

P2–P4 (Fig. 9F–G). Intercoxal sclerites rectangular with deeply concave ventral margins. Praecoxae triangular, small and naked. Coxae wider than long and without ornamentation. Bases smaller than coxae; anterior surface with a pore; outer basal seta absent in P2, naked and long (P3) or short (P4) in remaining legs; without ornamentation except for spinular row near base of P4 endopod. Exopods three-segmented; segments with coarse spinular ornamentation along outer margin, as illustrated; outer spine of segments naked (except for P2 exp-2 sparsely unipinnate); exp-3 with an outer unipinnate spine, and two setae distally (both naked in P2, one unipinnate and one bipinnate in P3–P4); outer spine of P2 exp-2 very long, extending far beyond exp-3 and about as long as entire exopod; P4 exp-2 elongate, distinctly longer than exp-1; segments of P4 about equally long, exp-3 with inner serrate seta in distal quarter originating from posterior surface. Endopods one- (P2–P3) or two-segmented (P4); P2–P3 endopods with few coarse spinules along both inner and outer margin; P4 enp-1 elongate, 3.7 times as long as enp-2, with few spinules along outer margin; P4 enp-2 without ornamentation; P2 endopod with long, apically serrate, backwardly directed seta along inner margin and one long unipinnate seta apically; P3 endopod shorter than P2 endopod, with short, naked spine apically; apical margin of P4 enp-2 with long, distally serrate and basally fused, inner seta, and short naked outer seta. Spine and seta formula as follows:

Fifth legs (Fig. 10A) closely set together, but not touching in ventral midline. Baseoendopod and exopod fused, forming a subrectangular plate; with one pore on anterior surface and two pores along inner margin; inner distal corner with strong, bipinnate, spinous process (homologous to inner spine); distal margin with a minute outer seta, one long naked seta, and two short, subequally long (outer one slightly longer), naked spines; outer basal seta long and naked.

Sixth pair of legs (Fig. 10A) reduced, fused medially forming common genital operculum; armature represented by vestigial spiniform element on either side. Copulatory pore conspicuous (arrowed in Fig. 10A).

Description of male. Total body length from tip of rostrum to posterior margin of caudal rami 235 µm (n = 1). Body ornamentation essentially as in female except for internal semicircular reinforcements present only on somites bearing P2–P4 (Fig. 11A). Sexual dimorphism in antennule, genital segmentation and P6. Spermatophore length approximately 33 µm.

Antennule (Fig. 11F) 9-segmented, haplocer; geniculation between segments 7 and 8. Segment 1 with a slender naked seta; segment 2 longest and about 2.4 times longer than wide, with one plumose and seven naked setae; segment 3 with four setae and a spine; segment 4 an incomplete sclerite with one seta and one spiniform element; segment 5 with a long aesthetasc (40 µm) fused basally to slender seta; segment 6 with a seta; segment 7 with a seta and a spine; segment apparently unarmed; distal segment with six setae (none of which spatulate) and apical acrothek consisting of short aesthetasc (10 µm) fused basally to two slender setae. Armature formula: 1-[1], 2-[7 + 1 plumose], 3-[4 + 1 spine], 4-[(1 + 1 spine)], 5-[1 + (1 + ae)], 6-[1], 7-[1 + 1 spine], 8-[0], 9-[6 + acrothek].

Sixth legs (Fig. 10B) slightly asymmetrical, with smallest P6 closing off functional gonopore; each with a long outer seta and a short inner spine, both elements being naked.

Etymology. The specific epithet is derived from the Latin super, meaning over, and s(a)eta, s(a)etosus, meaning bristle, bristly, and refers to the supernumerary element on the P5 of both sexes.

Remarks. Neoleptastacus supersetosus sp. nov. is assigned to the trisetosus -group based on (1) the absence of paired spinous processes on the anal somite, (2) a well-developed anal operculum, (3) P1 exp-1 without outer spine and exp-2 with three setae/spines, (4) P2 exp-2 with very long outer setiform element extending far beyond distal margin of exp-3, (5) endopod P2–P3 1-segmented with inner seta and one distal spine on P2 and one distal spine on P3, and (6) outer seta of P4 enp-2 reduced. Within this group it is morphologically closest to N. trisetosus and N. panamensis sp. nov. with which it shares the 2-segmented condition of the P1 exopod. Characters that differentiate the new species from these two congeners include (1) somites bearing P2–P5, genital double-somite and second abdominal somite with internal semicircular reinforcements in ♀, and on somites bearing P2–P 4 in ♂, (2) inner spine of P5 fused to segment, forming spinous process in both sexes (vs delimited at base), and (3) male P6 with outer seta and inner spiniform element (vs outer seta only). An additional character that differentiates N. supersetosus sp. nov. readily from all known species of Neoleptastacus (and in fact all other Arenopontiidae) is the presence of a supernumerary setiform element on the P5 of both sexes.