Macrolabrum distonyx, Bamber, 2007

Bamber, Roger N., 2007, New apseudomorph tanaidaceans (Crustacea, Peracarida, Tanaidacea) from the bathyal slope off New Caledonia, Zoosystema 29 (1), pp. 51-81 : 70-75

Macrolabrum distonyx n. sp.

( Figs 10-12 )

TYPE MATERIAL. — Holotype: New Caledonia, BIO- CAL, stn DW 66, 24°55.43’S, 168°21.67’E- 24°54.84’S, 168°21.99’E, 515- 505 m depth, 3.IX.1985, ♀ (MNHN- Ta929).

Paratypes:same data as holotype, 1 brooding ♀ (dissected) in a gastropod shell. — New Caledonia, BIOCAL, stn DW 77, 22°15.32’S, 167°15.40’E- 22°15.65’S, 167°15.49’E, 440 m depth, 5.IX.1985, 1 ♀, 2 specimens in gastropod shells (MNHN-Ta930) ; 1 brooding ♀ (NHM.2005.2715).

TYPE LOCALITY. — Off New Caledonia, 24°55.43’S, 168°21.67’E- 24°54.84’S, 168°21.99’E.

ETYMOLOGY. — From the Greek “ di ”, two, and “ stonyx ”, any sharp point, with reference to the two spine-like apophyses on the proximal antennal peduncle articles.

DESCRIPTION

Female

Body ( Fig. 10A ) typical of a pagurapseudid, pleon skewed to the right and curved under pereon; small, holotype about 3.25 mm long. Cephalothorax ( Fig. 10B ) subrectangular, as long as wide, with pronounced triangular rostrum with denticulate anterior margin, four lateral plumose dorsolateral setae behind on each side of cephalothorax, four pairs of simple setae middorsally; eyelobes conspicuous, eyes present, black. Epistome not protruding beyond anterior of rostrum. Six free pereonites; pereonites 1 to 3 subequal, pereonites 4 and 5 subequal, longer, pereonite 6 as long as pereonite 1; pereonites with one or two plumose setae on each lateral margin. Pleon of five free subequal pleonites, pleonites 1 and 2 only bearing pleopods, each pleonite about half as long as pereonite 5. Pleotelson ( Fig. 10C ) pentagonal, not as long as last two pleonites together, as wide as long, with single midlateral plumose seta, paired anterodorsal plumose setae and rows of three posterodorsal simple setae on each side.

Antennule ( Fig. 10E ) proximal peduncle article 3.8 times as long as wide, with numerous inner sharp apophyses and few outer sharp apophyses; second article 0.3 times as long as first, third article 0.9 times length of second, fourth article half length of second with minimal extension for accessory flagellum. Main flagellum of two segments subequal in length, distal segment narrower than proximal, each with single aesthetasc, distal segment with five distal setae; accessory flagellum of one segment, distally reaching just past proximal segment of main flagellum.

Antenna ( Fig. 10D ) with four-articled peduncle; elongate rectangular proximal article bearing inner distal plumose seta and outer distal spine-like apophysis; second article short, 1/4 as long as first, with outer distal spine-like apophysis; third article2.5 times as long as second, fourth article 1.3 times as long as third. Flagellum of two very small segments.

Labrum simple, rounded, distally setulose. Left mandible ( Fig.10F ) with quadricuspid pars incisiva, lacinia mobilis denticulate, setiferous lobe with five setae, pars molaris round, blunt, simple; palp of three articles, proximal article with long, plumose distal seta, second article longest with group of four inner subdistal setae, third article with two short and two long distal setae, each finely serrate in distal half. Right mandible as left but without lacinia mobilis.Labium ( Fig. 10G ) with denticulate outer margin, palp with single distal seta. Maxillule (not figured) typical for the genus, inner endite with four finely plumose distal setae, outer endite with 10 distal spines, outer margin sparsely setose, palp of two articles, distally with two setae. Maxilla (not figured) with rostral row of 11 setae and inner denticulate spine; fixed endite with two trifid and four simple setae and inner plumose seta; moveable endite lobes almost fused and with simple setae. Maxilliped endite with five slender distal spines and subdistal plumose seta; maxilliped basis naked; palp ( Fig. 11A ) proximal article with single plumose inner seta, outer margin with denticulate apophyses and with two plumose long setae; second article outer margin coarsely denticulate with two long plumose setae, inner margin dorsally with seven long plumose setae, marginally with five simple spines; third article with inner apophysis bearing one plumose and two longer and one shorter simple setae; distal article with one distal, five inner setae and two outer subdistal setae, all setae finely denticulate along proximal half. Epignath destroyed in dissection.

Right cheliped ( Fig. 11C ) with compact basis as long as wide, with paired subdistal, ventral plumose setae and two ventral marginal spines with finely bidenticulate margin towards distal end, spine-like apophyses dorsally, exopodite absent; merus quadrangular, subdistally with ventral denticulations, few setae; carpus compact, 1.5 times as long as wide, widening distally, with group of three proximal dorsal compound spines, marginal setae simple; propodus stout, quadrangular, 1.2 times as long as wide, with simple setae along ventral margin; fixed finger with five spines distally and large triangular apophysis proximally on cutting edge, moveable finger slender with proximal small triangular apophysis, distal bulge and small curved setae on cutting edge.

Left cheliped ( Fig.11D ) smaller than right cheliped, basis and merus similar to those of left cheliped; carpus more slender, 2.3 times as long as wide; propodus more slender, with denticulate ventral margin and hook-like spines on cutting edge of fixed finger.

Pereopod 1 ( Fig. 12A ) longest pereopod, basis twice as long as wide, dorsal margin extended as flange bearing eleven plumose setae, ventral margin with seven plumose setae; exopodite present, large, distal article with 16 plumose setae. Ischium with single long ventrodistal plumose seta. Merus as long as basis, ventral margin with six plumose setae alternating with six compound spines. Carpus shorter than merus, ventrally with three compound spines alternating with setae, distal seta not plumose. Propodus slender, longer than merus, with four ventral slender spines. Dactylus plus unguis slender, curved, 1.5 times as long as propodus, with three ventral spines with adjacent fine setae.

Pereopods 2 to 6 ( Fig. 12 ) similar to each other, progressively smaller, about 1/3 (pereopod 2) to 1/4 (pereopod 6) as long as pereopod 1; basis compact with single ventrodistal plumose seta, and additional two (pereopod 6) or three (pereopods 4 and 5) ventral plumose setae, single dorsal plumose setae on pereopods 3 to 5, two on pereopod 6; ischium with ventrodistal plumose seta and adjacent simple spine on pereopods 2 and 3. Merus, carpus and propodus bearing “sucker-like” spines and plumose setae as figured. Merus and carpus subequal on pereopods 2 and 3, carpus much longer than merus on pereopods 4 to 6. Propodus on all of these pereopods with distal seta with fine inner serrations, dactylus and unguis not fused into claw, dactylus with minute inner seta.

Pleopods ( Fig. 11B ) alike, biramous; basis with two dorsal plumose setae; exopod slender with five plumose setae, endopod almost circular with nine plumose marginal setae.Uropod( Fig.12G ) biramous, basis with one plumose and one simple outer seta; endopod longer than basis, of three segments, distal segment longer than proximal two, distally with plumose sensory seta and four stout spine-like setae; exopod of two segments, together as long as proximal two endopod segments, with two distal setae.

Male

Unknown.

REMARKS

Of the three gastropod-shell-inhabiting genera of the Pagurapseudinae , Pagurotanais Bouvier, 1918 is distinguished, inter alia, by the exopodite on pereopod 1 being reduced to one article or absent (see Guţu 1996a); Macrolabrum is distinguished from Pagurapseudes Whitelegge, 1901 by having an elongate epistome exceeding the anterior margin of the cephalon, large plumose setae on the maxilliped palp, and a serrated outer margin to the second article of that palp ( Guţu 1997). While these maxilliped features are present in M. distonyx n. sp., the epistome does not exceed the anterior margin of the cephalon. Guţu (1997) discussed the variability in this feature, and thus the difficulty in diagnosing these two genera. Generally, as here, Macrolabrum species show marked dimorphism in the chelae in the adult and have stout distal setae or spines on the uropod endopod.

Guţu (1997) produced a key to the five species of Macrolabrum then known: the only one of those species with pleopods, a two-segmented uropod exopod and a three-segmented uropod endopod is M. aenigmaticus Guţu, 1997 (from Bali, littoral), known only from juveniles. That species is distinct from M. distonyx n. sp. in its protruding epistome, its simple, distally bifurcate rostrum, and in having four segments in the main flagellum and two segments in the accessory flagellum of the antennule, inter alia.

The only species of Macrolabrum described since 1997 is M. impedimenta Bamber, 2006 , from southwestern Australia in 20 to 39 m depth. That species also has pleopods and one and two segments in the accessory and main flagella of the antennule respectively; however, M. impedimenta has a one-segmented uropod exopod and a two-segmented uropod endopod, simpler setation on the mandibular palp, and complete marginal rows of eight plumose setae on pereonite 1, as well as numerous differences in the setation of the pereopods (Bamber 2005).

The four-articled peduncle of the antenna in the present species is shared with M. rugosus Guţu, 1997 (other species having five articles); the proximal peduncle article in each of these species is elongate, and may represent the fusion of two articles. With a depth range of 440 to 515 m, the present species is by far the deepest recorded, the other six species having been taken in depths of less than 40 m.

Figures

FIG. 10. — Macrolabrum distonyx n. sp., ♀: A, holotype ♀, entire; B, cephalon, dorsal; C, pleotelson, dorsal; D, left antenna with detail of distal articles; E, left antennule; F, left mandible; G, labium. Scale bar: A, 0.7 mm; B, C, 0.4 mm; D, E, 0.3 mm; F, G, 0.1 mm.

FIG. 11. — Macrolabrum distonyx n. sp., ♀: A, maxilliped palp;B, second right pleopod (plumose nature of all setae not shown);C, right cheliped; D, left cheliped. Scale bar: A, B, 0.1 mm; C, D, 0.2 mm.

FIG. 12. — Macrolabrum distonyx n. sp., ♀: A, right pereopod 1, with detail of exopod;B-F, left pereopods 2-6 respectively; G, uropod. Scale bar: A, 0.2 mm; B-G, 0.1 mm.