Pseudotanais (Pseudotanais) tympanobaculum Błażewicz-Paszkowycz, Bamber & Cunha, 2011, sp. nov.

Pseudotanais (Pseudotanais) tympanobaculum sp. nov.

Figs 26–28

Type material. 1Ƥ, Holotype (BMNH.2010.422), 12ƤƤ (2 with empty brood-pouches), paratypes (BMNH.2010.423-432), 2 further females, dissected, Station CA 546, Captain Arutyunov mud-volcano, 35º39.692’N 07º20.046’W, 1345 m depth, mud-breccia and gas-hydrate, TV-grab, 0 6.08.2004, coll. MRC.

Other records. 2 specimens, Stn CA 393, Captain Arutyunov mud-volcano, 35º39.740’N 07º19.942’W, 1327 m depth, mud-breccia, TV-grab, 09.07.2002; 1 specimen, Stn Ki 528, Kidd mud-volcano, 35º25.304’N 06º43.972’W, 489 m depth, mud-breccia and H2S, TV-grab, 03.08.2004; 1 specimen, Stn CA 543, Captain Arutyunov mud-volcano, 35º39.688’N 07º19.981’W, 1345 m depth, mud-breccia and H2S, Gravity corer, 06.08.2004; 26 specimens, Stn CA 547, Captain Arutyunov mud-volcano, 35º39.701’N 07º20.037’W, 1344 m depth, mudbreccia and gas-hydrate, TV-grab, 06.08.2004; 2 specimens, Stn CA 548, Captain Arutyunov mud-volcano, 35º39.708’N 07º20.034’W, 1345 m depth, mud-breccia and H2S, Kasten-corer, 06.08.2004; 21 specimen, Stn Ki 559, Kidd mud-volcano, 35º24.777’N 06º43.782’W, 552 m depth, mud, Boxcorer, 08.08.2004; 2 specimens, Stn Ki 561, Kidd mud-volcano, 35º25.602’N 06º44.099’W, 526 m depth, mud, Boxcorer, 08.08.2004; 21 specimens, Stn Mer 576, Mercator mud-volcano, 35º17.657’N 06º39.129’W, 428 m depth, mud, Boxcorer, 26.07.2005; 2 specimens, Stn Bom 597, Bonjardim mud-volcano, 35º27.563’N 09º00.030’W, 3061 m depth, mud-breccia, TV-grab, 02.08.2005; all coll. MRC.

Description: body (Fig. 26 A, B) compact, holotype 2.4 mm long, four times as long as wide. Cephalothorax trapezoidal, two-thirds as long as wide, as long as pereonites 2 and 3 together, single setae in anterolateral corners, rostrum eyelobes and eyes absent. Pereonites naked; pereonite 1 shortest by far, pereonite 2 2.5 times as long as pereonite 1, pereonite 3 three times as long as pereonite 1, pereonites 4 and 6 subequal, four times as long as pereonite 1, pereonite 5 longest, five times as long as pereonite 1 (all pereonites respectively 7.7, 3.4, 3.2, 2.1, 1.7 and 1.9 times as wide as long). Pleonites becoming narrower posteriorly, each pleonite about 6.5 times as wide as long and bearing pleopods. Pleotelson semicircular but extended into blunt posterior apex, 2.5 times as long as each pleonite, nearly twice as wide as long, naked.

Antennule (Fig. 27 A) proximal article 4.5 times as long as wide, much longer than distal two articles together, with simple mesial seta, one longer and one shorter distal simple setae and two penicillate distal setae; second article 2.5 times as long as wide, 0.4 times as long as first article; third article nearly half as long as second article, distally with three simple, two bifurcate and one penicillate setae and one aesthetasc.

Antenna (Fig. 27 B) proximal article compact, naked; second article almost as wide as long, with small dorsodistal spine; third just longer than second, naked; fourth article longest, six times as long as wide, with four distal setae; fifth article 0.4 times as long as fourth, with one distal seta; sixth article minute with five distal setae.

Labrum (Fig. 27 C) rounded, naked. Left mandible (Fig. 27 D) with wide, crenulate lacinia mobilis, right mandible (Fig. 27 E) with crenulated upper margin; pars molaris of both mandibles acuminate with two or three fine subdistal denticles. Labium (Fig. 27 H) simple, bilobed, naked. Maxillule (Fig. 27 F) with nine distal spines and two fine setae, palp (Fig. 27 Fʹ) with two distal setae. Maxilla (Fig. 27 G) simple, ovoid, naked. Maxilliped (Fig. 27 I) first palp article naked, second article with one outer and two inner finely setulose setae, third article with two inner setae, fourth article with three inner, two distal and one outer subdistal setae; basis fused, naked; endites almost completely fused, distally with single seta and slight oval tubercle. Epignath (Fig. 27 J) elongate, distally pointed.

Cheliped (Fig. 28 A) with rounded, naked basis 1.4 times as long as wide; merus subtriangular, naked; carpus 1.6 times as long as wide, with single mid-dorsal and midventral setae; propodus 1.7 times as long as wide, with comb-row of one longer and eight shorter setae near base of dactylus; fixed finger 0.75 times as long as propodus, with one ventral seta and three setae adjacent to cutting edge; dactylus with small proximal seta, cutting edge with central fine spinule. Chela not forcipate.

Pereopod 1 (Fig. 28 B) coxa naked; basis slender, 5.5 times as long as wide with one mesial seta; ischium compact, with small ventral seta; merus 0.24 times as long as basis and with small ventrodistal seta; carpus as long as merus, naked; propodus nearly as long as carpus and merus together, with one dorsodistal seta; dactylus with distal seta and distinct slender unguis twice as long as dactylus, both together 1.45 times as long as propodus. Pereopod 2 (Fig. 28 C), coxa similar to but stouter than pereopod 1, basis 5.2 times as long as wide, with one ventroproximal seta; merus 0.35 times as long as basis and with slender, blunt ventrodistal spine; carpus as long as merus, with dorsodistal seta and blade-like ventrodistal spine; propodus 1.5 times as long as carpus, with ventrodistal spine; dactylus with slightly longer unguis together two-thirds as long as propodus. Pereopod 3 (Fig. 28 D) similar to but more compact than pereopod 2, merus ventrodistally with two spines and one small seta.

Pereopod 4 (Fig. 28 E) basis stout, 2.7 times as long as wide; ischium with two ventral setae; merus 0.4 times as long as carpus and with one ventrodistal spine; carpus with one simple and one blade-like spines, and two small ventrodistal setae; propodus 0.8 times as long as carpus, with two ventrodistal spines and dorsodistal spine longer than dactylus plus unguis; dactylus and unguis short, 0.6 times as long as propodus. Pereopod 5 (Fig. 28 F) as pereopod 4, but additional ventrodistal spine on carpus, single ventrodistal spine but additional dorsodistal seta on propodus. Pereopod 6 (Fig. 28 G) as pereopod 5, but stouter.

Pleopods (Fig. 28 H) all alike, with naked basis, slender endopod shorter than exopod and with four distal plumose setae, exopod with five distal plumose setae.

Uropods (Fig. 28 I) biramous, both exopod and endopod of two segments, setose as figured; exopod almost as long as endopod.

Male unknown.

Etymology. from the Latin tympanum – a drum, and baculum – a stick, thus drum-stick (noun in apposition), a term for the stout back legs of edible phasianid birds, the present species being characterized by stout bases on the posterior pereopods.

Remarks. The Pseudotanaidae of the northeast Atlantic was comprehensively analyzed by Bird and Holdich (1989), who included a key to the species then known. With its blade-like carpal spines on pereopods 2 to 6 (characteristic of the nominate subgenus Pseudotanais), distally-bifurcate setae on the antennule, one ventral seta on the non-forcipate chela, short inferodistal spines on the propodus of pereopods 2 and 3, and subequal uropod rami, of the species in that key P. tympanobaculum sp. nov. is closest to P. (P.) spicatus Bird & Holdich, 1989, recorded from the Rockall Trough, Porcupine Seabight and Abyssal Plain and Bay of Biscay at depths between 2227 and 4829 m. However, unlike the present species, P. (P.) spicatus has a small dorsodistal spine on the third article of the antennule, more inner setae on the second and third maxilliped palp articles, more complex and dendritic denticulation on the mandibular pars molaris, a one-segmented uropod endopod, many more setae on the pleopod rami, and, on the posterior pereopods, much more slender bases and a stouter, fused dactylus and unguis.

Of the two similar species described since 1989 (non-forcipate members of the nominate subgenus, with subequal uropod rami), Pseudotanais (P) baresnauti Bird, 1999 (q.v.) (from a Caribbean cold seep), which shares a naked merus with P. tympanobaculum, has subequal anterior pereonites, a simpler pars molaris, a small dorsodistal spine on the third article of the antennule, and more slender posterior pereopod bases; P. nipponicus McLelland, 2007 (q.v.) (from the Kurile-Kamchatka Trench) has more, or more complex setation on the maxilliped (palps, bases and endites) and maxillule, and particularly on the pereopod bases.

Indeed, other than the Antarctic species Pseudotanais (P.) nordenskioldi Sieg, 1977, only P. (P.) denticulatus Bird & Holdich, 1989 approaches P. tympanobaculum in having wide bases to the posterior pereopods, but in that species the bases are still 3.3 to 4 times as long as their greatest width.

The new species was collected from the Captain Arutyunov mud-volcano (type-locality), in the deep-water field within the Portuguese margin, at depths from 1327 to 1345 m, from the Kidd and Mercator mud-volcanoes in the El Arraiche field on the Moroccan margin, at 428 to 552 m depth, and from the Bomjardim mud-volcano in the western Moroccan field at 3061 m, on muddy-substrata.