Meromonakantha irregularis ( Hansen, 1913 )

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 : 16-20

Meromonakantha irregularis ( Hansen, 1913)

( Figs 9–11 )

Typhlotanais irregularis Hansen 1913 , 36–38; pl. 3, figs 5a–c.

Material examined. 2ƤƤ, 1 juvenile (MNHN-IU- 2010-2844), Vicking, PL272-2, ASPI 8, G11 Nyegga, 64°39.980ʹN 05°17.351ʹE, 733 m, 26/05/2006; 1Ƥ (MNHN-IU- 2010-2845), Vicking, PL277-7, ASPI 2, PP-V16 HMMV, 72°00.336ʹN 14°42.741ʹE, 1264 m, 06/06/2006; 1Ƥ (MNHN-IU- 2010-2846), Vicking, PL277-7, ASPI 3, PP-V16 HMMV, 72°00.335ʹN 14°42.732ʹE, 1264 m, 06/06/2006; 1Ƥ (one dissected) (MNHN-IU- 2010-2847), Vicking, PL277-7, ASPI 4, PP-V16 HMMV, 72°00.336ʹN 14°42.723ʹE, 1263 m, 06/06/2006; 1Ƥ (MNHN-IU- 2010-2848), Vicking, PL277-7, ASPI 8, PP-V16 HMMV, 72°00.336ʹN 14°42.746ʹE, 1263 m, 06/06/2006; 1Ƥ (3 slides dissected) (MNHN-IU- 2010-2849), Vicking, PL277-7, ASPI 6, PP-V14 HMMV, 72°00.335ʹN 14°42.746ʹE, 1263 m, 06/06/2006.

Description of female. Body ( Fig. 9 A, B) small, holotype 1.4 mm long, 6.1 times as long as wide. Cephalothorax trapezoidal, just longer than maximum width, shorter than pereonites 1 and 2 combined, with slight blunt rostrum, naked, eyes and eyelobes absent. Six free pereonites; pereonite 1 trapezoidal, wider anteriorly, 0.6 times as long as cephalothorax; pereonites 2, 3, 5 and 6 subequal in length, 0.9 times as long as pereonite 1; pereonite 4 longest, 1.1 times as long as pereonite 1 (all pereonites respectively 1.8, 1.8, 1.7, 1.2, 1.3 and 1.3 times as wide as long). Pleon of five free subequal pleonites bearing pleopods; each pleonite 4.4 times as wide as long, with one stout dorsolateral seta on each side. Pleotelson subrectangular, twice as wide as long, less than twice as long as last pleonite, with rounded extension bearing two setae mid-posteriorly ( Fig. 11 I).

Antennule ( Fig. 10 A) of three articles, proximal article 1.6 times as long as wide, 1.3 times as long as distal two articles together, tapering, with mesial and distal pairs of one penicillate and one simple setae; second article just longer than wide, tapering, 0.3 times as long as first article, with three simple distal setae; third article tapering, extended by inner distal triangular apophysis, with four distal setae and one aesthetasc.

Antenna ( Fig. 10 B) of six articles, proximal article compact, fused to cephalothorax, naked; second article twice as long as wide, 1.3 times as long as first article, with stout dorsodistal seta; third article as long as first article, 1.5 times as long as wide, with stout dorsodistal seta; fourth article longest, curved, three times as long as third article, 5.5 times as long as wide, with three penicillate and one simple distal setae; fifth article half as long as fourth with one distal seta; sixth article minute with four distal setae.

Left mandible ( Fig. 10 C) with three rounded teeth on pars incisiva, wide, crenulate lacinia mobilis, right mandible ( Fig. 10 D) without lacinia mobilis, pars incisiva bifurcate; pars molaris of both mandibles stout, crenulated with strong, rounded tooth-like marginal tubercles. Labium ( Fig. 10 G) simple, bilobed, finely setose, without palp. Maxillule ( Fig. 10 E) with eight distal spines, palp not retrieved. Maxilliped ( Fig. 10 F) palp first article naked, second article with one fine outer distal and three stouter inner setae, third article with four inner setae, longest seta exceeding tip of fourth article, fourth article with five distal and one outer subdistal seta; basis with single, long seta not reaching margin of endites; endites distally with two small setae and two oval tubercles, outer margin setulose.

Cheliped ( Fig. 11 A) basis in situ not reaching anterior edge of pereonite 1, rounded, as long as wide, with one dorsal seta; merus subtriangular with single ventral seta; carpus with rounded dorsoproximal extension, twice as long as wide, with two mid-ventral setae; propodus large, palm 1.3 times as long as wide and as long as basis, single seta adjacent to dactylus insertion, fixed finger as long as palm with two ventral and one inner setae, two setae on cutting edge which bears three teeth in distal half; dactylus with fine proximal seta.

Pereopod 1 ( Fig. 11 B) coxa without apophysis; basis slender, 7.5 times as long as wide, with dorsal penicillate seta; ischium compact; merus one-quarter as long as basis, naked; carpus 1.5 times as long as merus with two distal setae; propodus 1.4 times as long as carpus, with smaller ventrodistal and longer dorsodistal setae, and slight dorsodistal pointed apophysis; dactylus with longer slender unguis, both together three-quarters as long as propodus. Pereopod 2 ( Fig. 11 C), coxa similar to pereopod 1, basis 7.4 times as long as wide, with dorsal penicillate seta; ischium with one ventral seta; merus 0.8 times as long as carpus, with one ventrodistal seta; carpus with two ventral, one medial and one dorsal distal setae; propodus 1.4 times as long as carpus, with smaller ventrodistal and longer dorsodistal setae, and slight dorsodistal pointed apophysis; dactylus with longer unguis 0.7 times as long as propodus. Pereopod 3 ( Fig. 11 D) similar to pereopod 2.

Pereopod 4 ( Fig. 11 E) coxa fused; basis stouter, four times as long as wide; ischium with minute seta; merus and carpus subequal, merus with two short finely-denticulate ventrodistal spines, carpus with three short finelydenticulate ventrodistal spines and fine dorsodistal seta; propodus 1.4 times as long as carpus, with two short finely-denticulate ventrodistal spines, one dorsodistal seta and dorsal penicillate seta in distal half; dactylus and shorter unguis not fused, slightly curved, 0.6 times as long as propodus. Pereopod 5 ( Fig. 11 F) as pereopod 4, but basis with two penicillate setae, merus and carpus more compact. Pereopod 6 ( Fig. 11 G) as pereopod 5, but propodus with three dorsodistal setae.

Pleopods ( Fig. 11 H) all alike, with naked basis, endopod shorter than exopod, endopod and exopod without setae on inner margin, outer margins with respectively 7 and 11 plumose setae, proximal seta of each ramus separated from others.

Uropod ( Fig. 11 I) biramous, basis naked; exopod of one segment with single mid-length seta and one longer and one shorter distal setae; endopod longer than exopod, with vestigial articulation, two distal penicillate setae on proximal pseudosegment, three penicillate and four subequal simple setae distally.

Remarks. Meromonakantha irregularis was described originally (as Typhlotanais irregularis ) from the Iceland- Faeroe-Jan Meyen region at depths from 536 to 1939 m. The present material is recognizable as Hansen’s species despite his original description and figures being somewhat limited. Notable characters highlighted by Hansen (1913) are the one-segmented uropod exopod reaching the middle of the distal segment of the endopod, the first pereonite more than half as long as the carapace, the rounded posterior pereonites, the proportions of the articles of the antennules and antennae, and the proportionately large chela with fingers as long as the palm.

We have taken advantage of the present material to present a detailed description of the female of this species (Hansen, ibid., records a subadult male). Its occurrence on the Nyegga seep-site and the Håkon Mosby Mud Volcano was at depths between 763 and 1263 m respectively, on reduced sediments. Distribution of this species in the Rockall-Iceland-Faeroe region is collated by Bird (2001); Just (1970) and Brandt (1977) also recorded this species from off the coasts of Greenland.

The genus Meromonakantha was reviewed most recently by Błażewicz-Paszkowycz (2007).

Genus Obesutanais Larsen, Bła ż ewicz-Paszkowycz & Cunha, 2006

Figures

FIGURE 9. Meromonakantha irregularis (Hansen, 1913), female, A, dorsal; B, lateral. Scale lines = 0.1 mm.

FIGURE 10. Meromonakantha irregularis (Hansen, 1913), female, A, antennule; B, antenna; C, left mandible; D, right mandible; E, maxillule endite; F, maxilliped; G, labium. Scale lines = 0.1 mm.

FIGURE 11. Meromonakantha irregularis (Hansen, 1913), female, A, cheliped; B to G, pereopods 1 to 6 respectively; H, pleopod; I, uropod. Scale lines = 0.1 mm.