Mesotanais pinguiculus Błażewicz-Paszkowycz, Bamber & Cunha, 2011, sp. nov.

Mesotanais pinguiculus sp. nov.

Figs 23–25

Type material. 1Ƥ, Holotype (BMNH.2010.418), 1Ƥ, 2 neuters, paratypes (BMNH.2010.419-421), Station JB391, Jesus Baraza mud-volcano, 35º35.439’N 07º12.264’W, 1105 m depth, carbonate clay and mud-breccia, TVgrab, 0 9.07.2002, coll. MRC

Other records. 3ƤƤ, same data as holotype; 10 specimens, Stn TTR 416, TTR mud-volcano, 35º21.87’N 06º52.00’W, 695 m depth, mud and corals, TV-grab, 17.07.2002; 3 specimens, Stn Mek 541, Meknès mud-volcano, 34º59.103’N 07º04.435’W, 703 m depth, mud- breccia and H2S, TV-grab, 05.08.2004; 2 specimens, Stn Mek 581, Meknès mud-volcano, 34º59.178’N 07º04.353’W, 700 m depth, mud- breccia, TV-grab, 28.07.2005; 3 specimens, Stn Mek 586, Meknès mud-volcano, 34º59.146’N 07º04.380’W, 701 m depth, mud-breccia, TV-grab, 28.07.2005.

Description of female: body (Fig. 23 A, B) relatively stout, cephalothorax and pleon narrower than pereon; holotype 2.3 mm long, 5.7 times as long as wide. Cephalothorax laterally convex, 1.4 times as long as wide, as long as pereonites 2 and 3 together, with small rostrum, small eyelobes present (Fig. 23 C, D) but eyes absent, single anterolateral seta above each eyelobe. Pereonites laterally-rounded; pereonites 1 and 2 with paired anterolateral setae; pereonite 1 shortest and narrowest, just wider than cephalothorax; pereonites 2, 3 and 6 subequal (1.4 times as long as pereonite 1); pereonite 5 longer (1.8 times as long as pereonite 1); pereonite 4 widest and longest, twice as long as pereonite 1 (all pereonites respectively 2.2, 1.9, 2.0, 1.4, 1.5 and 1.9 times as wide as long). Each pleonite about 4.5 times as wide as long, with paired lateral setae and bearing pleopods. Pleotelson narrower than pleon, pentangular, as long as last two pleonites together, 1.7 times as wide as long, with two distal setae.

Antennule (Fig. 24 A) slender; first article 1.3 times as long as rest of appendage with single simple and a few penicillate setae medially and distally; second article half as long as third article, with one simple and two penicillate setae distally; third article with one aesthetasc and six simple setae distally.

Antenna (Fig. 24 B) of seven articles, proximal article compact, naked; second article 1.4 times as long as wide, with single ventrodistal seta and slender dorsodistal spine; third article just shorter than second, with slender dorsodistal spine; fourth article longest, as long as first three articles together and 6 times as long as wide, with single simple and penicillate setae centrally and three of each distally; fifth article 0.4 times as long as fourth, with two distal setae; sixth article very short, with two distal setae; seventh article minute, with three distal setae.

Labrum (Fig. 24 C) smoothly rounded, naked. Left mandible (Fig. 24 D) with crenulated incisor and wide lacinia mobilis; right mandible incisor (Fig. 24 Dʹ) bifurcated distally with crenulated upper margin; molar wide, rounded in upper margin and smoothly square at lower margin. Labium (Fig. 24 F) bilobed, external lobe large and smooth; inner lobe smaller and distally hirsute. Maxillule (Fig. 24 E) endite relatively short (five times as long as wide), with setulose inner and outer margins and with nine short robust spines distally. Maxilla (Fig. 24 E) subtriangular. Maxilliped (Fig. 24 G) palp first article naked, second article with one outer and four inner setae, distal-most inner seta reaching distal margin of third palp article; third article with three proximal inner spinules, five marginal and two submarginal inner setae; fourth article with four distal, one inner and one subdistal setae; basis (not figured) with two unequal distal setae, shorter seta reaching distal edge of first palp article, longer seta just exceeding distal edge of second palp article; endites (Fig. 24 Gʹ) distally with one simple and one setulose inner setae and four robust spatulate spines. Epignath (Fig. 24 H) elongate, bipartite, with setose margin distally.

Cheliped (Fig. 24 I, Iʹ) with rounded, compact basis 1.2 times as long as wide; merus subtriangular with single ventral seta; carpus twice as long as wide, with three midventral setae, single proximal and distal dorsal setae; propodus elongate, as long as carpus, fixed finger with two ventral and three inner setae, cutting edge crenulate, setal row at base of dactylus of two setae; dactylus with proximal outer seta and two fine spinules on cutting edge.

Pereopod 1 (Fig. 25 A) longer than other pereopods, coxa with long seta; basis very slender, 11.3 times as long as wide, with single dorsoproximal seta; ischium compact with one ventral seta; merus 0.8 times as long as carpus, with single ventrodistal seta; carpus with two smaller ventrodistal setae, one longer dorsodistal seta more than half length of propodus; propodus as long as carpus and merus together, with two dorsodistal setae on slight mound, one ventrodistal seta; dactylus slender with single proximal seta, extending into slightly shorter slender unguis, the two together some 1.2 times as long as propodus. Pereopod 2 (Fig. 25 B) slender, similar to pereopod 1, basis 7.3 times as long as wide; merus 0.75 times as long as carpus, carpus with three small dorsodistal setae and single ventrodistal seta; dactylus and unguis together half as long as propodus. Pereopod 3 (Fig. 25 C) similar to pereopod 2, but carpus with three distal setae and ventrodistal spine.

Pereopod 4 (Fig. 25 D) basis less slender than those of anterior pereopods, 4.4 times as long as wide; ischium with two setae; merus 0.7 times as long as carpus, with two slender ventrodistal spines; carpus with outer, ventral and inner distal spines and one dorsodistal seta; propodus longer than carpus, with two slender distal spines, three distal setae as long as dactylus; dactylus and unguis together half as long as propodus. Pereopod 5 (Fig. 25 E) as pereopod 4, but basis with two penicillate setae and simple dorsoproximal seta. Pereopod 6 (Fig. 25 F) as pereopod 4, but basis with penicillate seta.

Pleopods (Fig. 25 G) all alike, with single dorsal plumose seta on basis; endopod shorter than exopod, and with single dorsal, single ventroproximal and 10 ventrodistal plumose setae; exopod with separated ventroproximal and 17 ventral plumose setae.

Uropod (Fig. 25 H) biramous, basis naked; exopod of two segments with weak articulation, proximal segment with single distal seta, second segment with three distal setae; endopod of four segments, proximal segment short, naked, weakly articulating, distal segments very slender, setose as figured.

Male: unknown.

Etymology. from the Latin pinguiculus – somewhat fat (diminutive of pinguis), referring to its having a lessattenuate body form than any of its congeners.

Remarks. The only known deep-water genera of the Leptocheliidae are Bathyleptochelia Larsen, 2003, and Mesotanais. Bathyleptochelia has eyes, no spines on the antennule articles 2 and 3, the dactylus and unguis of pereopods 4 to 6 fused into a claw, and a characteristic maxillule with only six distal spines. Mesotanais is the only leptocheliid genus without eyes (although eye-lobes are present), but dorsodistal spines are present on antennule articles 2 and 3, the unguis of the posterior pereopods is distinct, and the maxillule has nine distal spines. The present species thus accords with Mesotanais.

The six previously described species of Mesotanais are keyed out in Larsen & Shimomura (2007); M. pinguiculus sp. nov. is distinct from all of these (and thus fails at couplet 4 of the key) in having four spatulate spines distally on the maxilliped endite, all of the other species having either three or two. The present species, with its laterally convex pereonites and a body less than six times as long as wide, is also the least attenuate species, all others being long and slender in their habitus (from 6.6 to 9 times as long as wide) with a parallel-sided pereon.

These differences are not considered of sufficient significance to warrant attribution of this species to a new genus, rather that they reflect intrageneric variation.

Mesotanais pinguiculus shares the long dorsodistal seta on the carpus of pereopod 1 with only M. elongatus Sieg & Bird, 1989 and M. longisetosus Sieg & Heard, 1989; M. elongatus has two distal spatulate spines on the maxilliped endite and is nine times as long as wide, while M. longisetosus has very long distal setae on the antennule (longer than half the length of the antennule), has three distal spatulate spines on the maxilliped endite and is over eight times as long as wide; M. pinguiculus is also distinct in having proportionately longer distal spines on the merus and carpus of the pereonites than any other species.

There are now three species of Mesotanais recorded from this area of the North Atlantic, with the generotype M. dubius Dollfus, 1897 known from the Azores at 1287 m depth, while M. elongatus was found in the Strait of Gibraltar at 1255 m depth. Mesotanais styxis Larsen, Błażewicz-Paszkowycz & Cunha, 2006 is recorded from vents on the Mid-Atlantic Ridge (1709–1750 m), the remaining species being from the Gulf of Mexico (M. longisetosus, at 545–1386 m depth, and M. vadicola Sieg & Heard, 1989, at 22–865 m) and the west Pacific Ocean (M. birdi Larsen & Shimomura, 2007, at 186– 169 m).

Mesotanais pinguiculus was collected from the Jesus Baraza mud-volcano (type-locality) in the western Moroccan field at 1105 m, and from the TTR and Meknès mud-volcanoes on the Moroccan margin at depths from 695 to 703 m, on muddy-substrata.