Anarthrura edentatus, Bird, Graham, 2004

Bird, Graham, 2004, Tanaidacea (Crustacea) of the Northeast Atlantic: non­filiform species of Anarthruridae Lang from the Atlantic Margin, Zootaxa 471, pp. 1-44 : 12-16

Anarthrura edentatus sp. nov. ( Figs. 3–5 )

Anarthrura sp.5: Holdich & Bird, 1989: tables III, IV and appendices as taxon ‘29’. Anarthrura sp.AM#5: Bird, 2001: 26 –27.

Diagnosis. Anarthrura with distinct pleonites. Cheliped fixed finger with smooth incisive margin. Uropod endopod three times as long as basal article.

Material examined. Holotype neuter ( NMSZ:1999.238.0275), AFEN 1998 Stn 54587#1. Allotype early preparatory male ( NMSZ:1999.218.2092), AFEN Stn 54592#2. Paratypes AFEN 1998 Stn 54587#1, one neuter ( NMSZ:1999.238.0276); SMBA Stn ES18, one manca­II, two neuters, one prep. male; SBC64, two mancae­II, one manca­III, two neuters, one prep. male; SBC65, two mancae­II, one neuter; SBC168, two mancae­II, three mancae­III, three neuters, one ovigerous female; SBC279, eight neuters, two prep. males, three incomplete specimens ( NHM 1988:551–557 and 1989:912:13 for SMBA material).

Also seen: IOS Stn 51403#2, one specimen; ‘Chain 106’ Stn 313, one specimen.

Description. Neuter/non­ovigerous female. Body ( Fig. 3 A) fairly slender, 6.6 times longer than broad. Length 1.40–1.98 mm (holotype 1.85 mm). Cephalothorax short, 17% of body length, with convex caudal margin and tapering rostral third; rostrum ( Fig. 3 B) small, and area behind attachment of antennules with lateral creases. Pereonites 1–6 weakly subhexagonal or subrectangular, 0.63, 0.78, 0.89, 1.0, 0.82, and 0.67 times as long as broad respectively. Pleon ( Fig. 3 C) short and weak, only 11% of body length, pleonites with low rounded sternites, that of pleonite­1 most prominent. Pleotelson ( Fig. 3 D) half as long as pleon, wider than long, and with round apex.

Antennule ( Fig. 3 E) just longer than cephalothorax; article­1 0.44 times total length, 2.7 times longer than broad, article­2 half as long as article­1, article­3 half length of article­2, article­4 just longer than article­2, setation as figured. Antenna ( Fig. 3 F) 84% length of antennule, article­2 1.5 times longer than broad, article­3 smaller, both without dorsal setae; article­4 about six times longer than broad, with two sensory and two long setae; article­5 0.6 times as long as article­4, with distal seta; article­6 small, with one thickened (fused?) and two small setae.

Labrum ( Fig. 3 G) small, conical, not readily visible in whole specimens. Mandibles ( Fig. 3 H) small, ovoid. Maxillule endite ( Fig. 3 J) with (at least) four terminal spiniform setae. Maxilla ( Fig. 3 J) elongate ovoid. Maxilliped ( Fig. 3 K) bases small, without setae; endites simple, each with a long medial seta and shorter lateral seta.

Cheliped ( Fig. 4 A) pseudocoxa 1.7 times longer than broad, with dorsodistal seta; basis subcylindrical, with dorsal seta; merus with ventral seta; carpus broadly oval, 1.5 times longer than broad, with two dorsal setae and two ventral setae; propodus longer than carpus, 2.4 times longer than broad, with long anterior spiniform seta; fixed finger with seta at articulation with dactylus, one ventral seta and three spiniform setae associated with incisive margin, terminal spine tapering, incisive margin convex without dentition; dactylus with strong anterior spiniform seta.

Pereopods 1–3 similar, coxa with seta; other setation sparse. Pereopod­1 ( Fig. 4 B) basis slender, 4.6 times longer than broad; ischium with seta; merus 2.75 times longer than broad, with one seta; carpus about twice as long as broad, with curved dorsodistal seta and small ventrodistal seta; propodus longer than carpus, with long distal seta; dactylus and unguis 1.8 times longer than propodus, dactylus with accessory seta and unguis tip slightly expanded, blunt (possibly with spinning pore?). Pereopod­2 ( Fig. 4 C) basis with sensory seta, merus and carpus shorter than in pereopod­1; dactylus and unguis shorter, 1.3 times longer than propodus; overall 86% of pereopod­1 length. Pereopod­3 ( Fig. 4 D) basis, merus, carpus and propodus shorter than pereopod­2, overall 72% of pereopod­1 length.

Pereopod­4 ( Fig. 4 E) basis 4.2 times longer than broad; ischium with one seta; merus twice as long as broad, with two ventral spiniform setae; carpus subrectangular, as long as merus, with three spiniform distal seta and a smaller dorsodistal seta; propodus as long as carpus but only half as broad, with two spiniform ventrodistal setae and a longer dorsodistal spiniform seta; dactylus and unguis about two­thirds length of propodus. Pereopods 5– 6 ( Figs. 5 A–B) as above but with long sensory seta on basis and pereopod­6 propodus with four distal spiniform seta.

Uropod ( Fig. 5 C) about twice as long as pleotelson, clearly visible from dorsal view; exopod twice as long as broad and half length of basal article, with three unequal distal and terminal setae; endopod 3.2 times longer than basal article and eight times longer than broad, one­articled although with appearance of a weak articulation near insertion of two large sensory setae, with four long distal and terminal setae and two weaker terminal setae.

Manca­II. Generally as above but with shorter pereonites and pereopods­6 absent. Length 0.98–1.20 mm.

Manca­III. Similar to manca­II but with larger pereonite­6 and with rudimentary pereopods­6. Length 1.20 mm.

Preparatory male. Generally similar to neuter/non­ovigerous female. Body fairly slen­ der, 6.5 times longer than broad. Pleon ( Fig. 5 E) 20% of body length. Antennule ( Fig. 5 F) broader than in neuter/non­ovigerous female. Pleopods ( Fig. 5 G) present, elongate­ovoid, without setae in early moult stage, later with terminal setae. Length 1.41–1.75 mm.

Type locality. AFEN Stn 54587#1, Hebrides Slope, 57o 05.50’N 9o 25.84’W, 1498m, sandy mud.

Etymology. Latin edentatus , ‘toothless’, referring to the smooth incisive margin of the cheliped fixed finger.

Remarks. It is unusual for tanaids to have a cheliped fixed finger devoid of teeth. It is a bathyal Anarthrura species from the North Feni Ridge, northern Rockall Trough and the Hebrides, Malin and Porcupine Slopes, 1206–1832m; two of the records describe the sediment as ‘sandy mud’.

Figures

FIGURE 3. Anarthrura edentatus. A, non­ovigerous female; B, rostral part of cephalothorax; C, pleon and pleotelson, lateral view; D, pleotelson and pleonite 5; E, antennule; F, antenna; G, labrum, lateral view; H, mandible; J, maxillule endite and maxilla; K, maxilliped palp and endite. Scale bar 1 mm (A, C), 0.5 mm (B, D), 0.25 mm (E – F), 0.17 mm (K), 0.1 mm (G – J).

FIGURE 4. Anarthrura edentatus. Non­ovigerous female A, cheliped; B – E, pereopods 1 – 4 respectively. Scale bar 0.25 mm (A – E).

FIGURE 5. Anarthrura edentatus. Non­ovigerous female A – B, pereopods 5 – 6, with enlargements of complex setae; C, uropod; preparatory male D, dorsal view; E, pleon and pleotelson, lateral view; F, antennule; G, pleopod, with rudimentary setae. Scale bar 1 mm (D – E), 0.25 mm (A – C, F – G).