Obesutanais depilator, Błażewicz-Paszkowycz, Magdalena & Bamber, Roger N., 2011

Błażewicz-Paszkowycz, Magdalena & Bamber, Roger N., 2011, Tanaidomorph Tanaidacea (Crustacea: Peracarida) from Mud-Volcano and Seep Sites on the Norwegian Margin, Zootaxa 3061, pp. 1-35 : 20-25

Obesutanais depilator sp. nov.

( Figs 12–14)

Material examined. Holotype, Ƥ (MNHN-IU-2010-2850), Vicking, PL277-7, ASPI 7, PP-V16 HMMV, 72°00.336ʹN 14°42.749ʹE, 1263 m, 06/06/2006. Paratypes: 1Ƥ (3 slides, dissected) (MNHN-IU- 2010-2851), Vicking, PL277-7, ASPI 2, PP-V16 HMMV, 72°00.336ʹN 14°42.741ʹE, 1264 m, 06/06/2006; 1Ƥ (MNHN-IU- 2010- 2852), Vicking, PL277-7, CL8, PP-V16 HMMV, 72°00.335ʹN 14°42.757ʹE, 1262 m, 06/06/2006; 1Ƥ (MNHN-IU- 2010-2853), Vicking, MTB-5, HMMV, 72°00.177ʹN 14°43.958ʹE, 1272 m, 07/06/2006; 2ƤƤ (MNHN-IU- 2010- 2854), ARK 22-1, PL170-7, CL12, HMMV, 72°00.34ʹN 14°43.22ʹE, 1259 m, 03/07/2007.

Description of female. Body ( Fig. 12) compact, holotype 1.4 mm long, about six times as long as wide. Cephalothorax subrectangular, with slight blunt rostrum, naked, eyes absent but rounded eyelobes present. Six free pereonites; pereonites 1 to 3 subequal, shorter than posterior pereonites, 0.3 times as long as cephalothorax; pereonites 4 and 5 subequal in length, just over twice as long as pereonite 1; pereonite 6 shorter, 0.7 times as long as pereonite 5. Five free subequal pleonites bearing pleopods; each pleonite one-third as long as pereonite 6. Pleotelson subrectangular, three times as long as last pleonite, with rounded extension mid-posteriorly.

Antennule ( Fig. 13 A) proximal article 2.7 times as long as wide, 1.5 times as long as distal two articles together, tapering, with inner and outer mesial penicillate setae, two fine outer setae in proximal half and one simple and two penicillate outer-distal setae; second article 1.3 times as long as wide, tapering, one-quarter as long as first article, with two simple distal setae and one inner distal penicillate seta; third article tapering, extended by inner distal triangular apophysis, twice a slong as second article, with five simple and one penicillate distal setae and one aesthetasc.

Antenna ( Fig. 13 B) of six articles, proximal article compact, fused to cephalothorax, naked; second article swollen, twice as long as first article, with dorsodistal seta and dorsal microtrichia; third article as long as first article, with dorsodistal seta; fourth article longest, curved, 3.8 times as long as third article, 4.3 times as long as wide, with three penicillate and three simple distal setae and dorsal microtrichia; fifth article 1.5 times as long as third with one distal seta; sixth article one-quarter as long as fifth with four distal setae.

Labrum ( Fig. 13 C) rounded, hood-shaped, densely setose. Left mandible ( Fig. 13 D) with four rounded teeth on pars incisiva, wide, subtly-crenulate lacinia mobilis, right mandible ( Fig. 13 E) without lacinia mobilis, pars incisiva bifurcate; pars molaris of both mandibles with stout, rounded marginal “teeth”. Labium ( Fig. 13 H) simple, bilobed, outer lobe with marginal microtrichia, inner lobe with outer distal setules, without palp. Maxillule ( Fig. 13 F) endite with eight distal spines and marginal microtrichia, palp not recovered. Maxilla ( Fig. 13 G) subovoid, naked. Maxilliped ( Fig. 13 I) palp first article naked, second article with one fine outer distal and two simple and one finely-denticulate inner setae ay distal corner, third article with two distally-denticulate and one simple inner setae and one simple distal seta exceeding tip of fourth article, fourth article with five distally-denticulate distal setae and one outer subdistal simple seta; basis with single, long seta exceeding margin of endites; endites distally with two setae and two oval tubercles, outer margin setulose.

Cheliped ( Fig. 14 A) with stout rounded basis 1.25 times as long as wide with one dorsal seta; merus subtriangular with single ventral seta; carpus with rounded dorsoproximal extension, 1.6 times as long as wide, with two mid-ventral setae and one fine more distal seta, single proximal and distal dorsal marginal setae; propodus large, longer than carpus, palm 1.1 times as long as wide with single seta adjacent to dactylus insertion, fixed finger as long as palm with two ventral setae, three setae on crenulate cutting edge; dactylus with fine proximal seta.

Pereopod 1 ( Fig. 14 B) coxa without apophysis, with seta; basis slender, 7.5 times as long as wide, with proximal dorsal row of fine setules; ischium compact, with one ventral seta; merus 0.4 times as long as basis, with single dorsodistal and ventrodistal setae; carpus 1.4 times as long as merus with two dorsodistal setae; propodus 1.1 times as long as carpus, with single smaller ventrodistal and longer dorsodistal setae, and slight dorsodistal pointed apophysis; dactylus half as long as slender unguis, both curved, together 0.9 times as long as propodus. Pereopod 2 ( Fig. 14 C), similar in proportions to pereopod 1, but ventrodistal setae on merus and carpus longer than their respective articles, dorsodistal setae on carpus and merus more than half as long as their respective articles, dactylus with distal seta. Pereopod 3 ( Fig. 14 D) stouter, basis 4.2 times as long as wide, with few ventral microtrichia; ischium with one ventral seta; merus 0.7 times as long as carpus, with one ventrodistal seta and distal crown of fine spinules; carpus with one ventral and one dorsal distal setae, and one small ventrodistal spine; propodus 1.6 times as long as carpus, with smaller ventrodistal and longer dorsodistal setae, and slight dorsodistal pointed apophysis; dactylus with longer unguis 0.6 times as long as propodus.

Pereopod 4 ( Fig. 14 E) coxa fused; basis three times as long as wide, with dorsal and ventral marginal rows of fine spinules; ischium with one ventral seta; merus and carpus subequal in length, merus with two short ventrodistal spines and ventral fields of microtrichia; carpus with three short finely-denticulate curved distal spines and fine dorsodistal seta, dorsal, outer and inner rows of microtrichia; propodus 1.6 times as long as carpus, with denticulate dorsal margin, two fine ventrodistal spines, one strong dorsodistal seta more than twice as long as dactylus plus unguis, and dorsal penicillate seta in proximal half; dactylus stout with ventrodistal apophysis, nearly four times as long as distinct bifurcate unguis, together one-third as long as propodus. Pereopod 5 ( Fig. 14 F) similar pereopod 4, but basis with two penicillate and two simple setae, dactylus with setulose ventral margin. Pereopod 6 ( Fig. 14 G) as pereopod 4, but basis with dorsal marginal spinules only, propodus with three dorsodistal setae.

Pleopods ( Fig. 14 H) all alike, with naked basis, endopod shorter and narrower than exopod, endopod and exopod without setae on inner margin, endopod with three distal plumose setae, exopod with six distal and one proximal plumose setae.

Uropod ( Fig. 14 I) biramous, basis naked; exopod of one segment with single mid-length seta and one longer and one shorter distal setae; endopod twice as long as exopod, with two flaccid blunt setae in proximal half and two penicillate and one shorter and four longer simple setae distally.

Male unknown.

Etymology. From the Latin depilis – without hair, this species being distinguished from the generotype by not having fields of setules on the bases of the pereopods (noun in apposition).

Remarks. The only previously-described species of Obesutanais is O. sigridae Larsen et al., 2006 , from 1675 to 1710 m depth on the Mid-Atlantic Ridge in the Lucky Strike hydrothermal-vent field, although a second species was noted (but not described) by Larsen (2006, as Typhlotanais sp.) from 3232 m on the Gorda Ridge, part of the Juan de Fuca Ridge hydrothermal-vent system in the north-east Pacific. As well as its gross morphology, characterizing features of that genus shown also by the present species are the bifurcate unguis on pereopods 4 to 6, the large gap between the proximal seta and the distal setae on the pleopod exopod, and the long ventrodistal seta on the merus and long ventrodistal and dorsodistal setae on the carpus of pereopod 2. Unusually, both species also show a much shorter merus-carpus-propodus on pereopod 3 than on pereopod 2 (not cited as a diagnostic character by Larsen et al. 2006).

Obesutanais depilator sp. nov. is distinguished from O. sigridae in having no “pseudo-articulation” and slen- der rather than “thick” setae on the uropod endopod, fewer marginal setae and a shorter distal seta on the antennular proximal article, two (rather than one) distal oval tubercles on the maxilliped endite, and it is without the dense scattering of setules over the bases of the pereopods.

Błażewicz-Paszkowycz et al. (2011) speculated that the genus Obesutanais might be endemic to chemicallyreduced habitats, and the discovery of O. depilator on the Håkon Mosby Mud Volcano would seem to confirm this. Obesutanais depilator was taken at a depth of 1263 m, amongst bacterial mats on the HMMV.

Figures

FIGURE 13. Obesutanais depilator sp. nov., female, A, antennule; B, antenna; C, labrum; D, left mandible; E, right mandible; F, maxillule endite; G, maxilla; H, labium; I, maxilliped. Scale lines = 0.1 mm.

FIGURE 14. Obesutanais depilator sp. nov., female, A, cheliped; B to G, pereopods 1 to 6 respectively; H, pleopod; I, uropod. Scale lines = 0.1 mm.