Synanarthrura celtica Bird, 2004, sp. nov.

Synanarthrura celtica sp. nov. (Figs. 17–18)

Anarthruropsis sp.A: Holdich & Bird, 1985: 443 table 1.

Anarthrura sp.1: Holdich & Bird, 1989: tables III, IV and appendices as taxon ‘25’.

Material examined. Holotype: BIOGAS VI Stn DS86, neuter, (MNHN). Paratypes: SMBA Stn SBC160, five mancae­II, three neuters (NHM 1988:539).

Description. Neuter/non­ovigerous female. Body (Fig. 17 A) fairly stout, 5.5 times longer than broad. Length 1.7–2.46 mm. Cephalothorax relatively large, 18 % of body length, as wide as long, tapering for rostral third, and with shallow caudal medial cleft. Pereonites 1 and 2 narrower caudally; pereonites 3–6 with rounded corners, 0.36, 0.47, 0.58, 1.0, 1.0 and 0.77 times as long as broad respectively. Pleon 15% of body length, slightly narrowing caudally into pleotelson, epimera with marginal seta. Pleotelson (Fig. 17 B) just over half as long as broad, subrectangular apart from small apical process, bearing group of three setae on each caudolateral margin and four terminal setae.

Antennule (Fig. 17 C) three­quarters length of cephalothorax, article­1 2.6 times longer than broad, article­2 twice as long as article­3, article­4 with six terminal setae and one aesthetasc, other setation as figured. Antenna (Fig. 17 D) nearly three­quarters length of antennule, article­2 half as long as article­3, both with a small dorsal seta, article 4 with ‘pseudoarticulation’ bearing a sensory seta, with three distal setae, article­6 small with five unequal setae.

Labrum (Fig. 17 E–F) ovoid in lateral view, elongate and laterally compressed. Labium (Fig.17 G) simple, but with median cleft. Mandibles (Figs. 17 E–F) small, with broad crenulate incisor process and an apparently sharply acuminate molar process. Maxillule endite (Fig. 17 H) with five unequal spiniform setae, one of which is broader than others and may be derived from two fused setae, with some delicate distal setae. Maxilliped (Fig. 18 B) basis with seta at base of palp; endites long and conical, with setose distal margin; palp with small article­1 and large article­2 bearing one long seta and two stouter serrate setae; article­3 largest, with three large plumose setae and smaller medial seta; article­4 (Fig. 18 B) subrectangular, with five long plumose setae and fringe of smaller distal setae. Epignath (Fig. 17 J) linguiform.

Cheliped (Fig. 17 K) pseudocoxa 1.3 times longer than broad; basis with dorsal seta; merus with one ventral seta; carpus with dorsal margin twice as long as free ventral margin, with proximal and distal setae, ventral margin with rounded triangular process and one seta; chela (Fig. 18 A) with dactylus and fixed finger bent in opposition, propodus with lateral ridge; fixed finger with weakly convex incisive margin with complex dentition, with three guard setae and seta at articulation with dactylus; terminal spine slightly deflexed, elongate cone­shaped; dactylus strongly curved and tapered, with large anterior spiniform seta.

Pereopod­1 (Fig. 18 C) basis curved, 4.5 times longer than broad; ischium with one seta; merus with two unequal setae; carpus subrectangular, slightly expanded distally, with four distal setae; propodus four times longer than broad, with small dorsal setae and thin bifid distoventral seta; dactylus and unguis as long as propodus, dactylus with accessory seta. Pereopods 2–3 (Fig. 18 C, pereopod 3 not figured) with shorter basis, merus and carpus.

Pereopods 4–6 (Figs. 18 E–F, pereopod­6 not figured) basis broad, 2.5 times longer than broad; ischium with two setae; merus with two spiniform setae; carpus subrectangular, twice as long as broad, with three spiniform setae with complex tips, and one smaller bifid seta; propodus two­thirds length of carpus, with two (pereopods 4–5) or three (pereopod­6) ventrodistal spiniform setae and one long dorsodistal spiniform seta; dactylus and unguis shorter than propodus.

Pleopod (Fig. 18 G) endopod small and rectangular, with five terminal plumose setae; exopod possibly two­articled, proximal bearing a seta, and distal with seven distal plumose setae.

Uropod (Fig. 18 H) about as long as pleotelson, exopod nearly half as long as endopod, with three distal and terminal setae; endopod 5.5 times longer than broad, with one distal and four terminal setae.

Type locality. South Biscay Slope, 1950 m.

Etymology. Latin celtica alludes to known distribution off the Celtic fringe of the British Isles and France.

Remarks. A rarely collected lower bathyal/upper abyssal species known only from the type locality and the Porcupine Seabight Justification for the inclusion of this species is its similarity to Anisopechys crinitus sp. nov. together with the possibility that it could be recorded from the more northern part of the Atlantic Margin.