Macrolabrum mansoris, Bamber, 2009

Bamber, Roger N., 2009, Two new species of shell-inhabiting tanaidaceans (Crustacea, Peracarida, Tanaidacea, Pagurapseudidae, Pagurapseudinae) from the shallow sublittoral off Vanuatu, Zoosystema 31 (3), pp. 407-418 : 412-417

Macrolabrum mansoris n. sp.

( Figs 3 ; 4 )

TYPE MATERIAL. — Holotype: Vanuatu, SANTO 2006 , stn DB63, Aégé Island , 15°26.5’S, 167°15.50’E, 21 m depth, 25.IX.2006, 1 ♀ with 16 mancae in shell (MNHN-Ta 958) . Paratypes: same data as holotype, 1 ♀ with 17 mancae in shell (MNHN-Ta 959) ; 1 ♂, 1 brooding ♀ ( BMNH.2007.962-963) ; 8 ♀♀ (5 brooding); 2 ♂♂, 2 other specimens, paratypes (MNHN-Ta960); 2 ♀♀ (one with oostegites), 1 ♂, dissected (coll. R. Bamber). — Stn FB52, Malo Island (Kili Kili), 15°28.2’S, 167°15.0’E, 7 m depth, 5.X.2006, 6 ♂♂, 4 ♀♀, 11 other specimens (MNHN-Ta 961) .

TYPE LOCALITY. — Off Vanuatu, 15°26.5’S, 167°15.50’E, 21 m depth.

ETYMOLOGY. — Mansoris – Latin, a guest or sojourner, noun in apposition.

DESCRIPTION OF FEMALE

Body typical of a pagurapseudid, pleon skewed to right and curved under pereon; small, holotype about 3.8 mm long. Cephalothorax ( Fig. 3A ) square with straight anterior margin, rostrum represented by truncate extension with medial and lateral tubercles; single simple seta behind ocular lobe, followed by row of five plumose lateral setae. Eyelobes distinguished, eyes present as group of black-pigmented ocelli. Epistome large, exceeding tip of rostrum. Six free pereonites; pereonite 1 shortest, one-third length of cephalothorax, with three anterolateral plumose setae; pereonite 2 1.2 times as long as pereonite 1, with paired anterolateral plumose setae; pereonites 3 to 6 subequal, 1.5 times as long as pereonite 2, with paired anterolateral plumose setae. Pleon of five free subequal pleonites, each pleonite about 0.8 times as long as posterior pereonites and bearing three mid-lateral plumose setae. Pleonites 1 and 2 only bearing pleopods. Pleotelson ( Fig. 3B ) subrectangular, 1.5 times as long as pleonite 6, as long as its maximum width, with paired plumose lateral setae, paired simple dorsolateral setae and paired posterodorsal setae as figured. No apparent pigmentation (in preserved material).

Antennule ( Fig. 3C ) proximal peduncle article 4.3 times as long as wide, with row of inner blunt spine-like apophyses accompanied by plumose setae, no distal apophysis; second peduncle article 0.4 times as long as first; third article as long as second, fourth article 0.3 times as long as third. Main flagellum of three segments, with single aesthetascs on each segment; accessory flagellum of one slender segment, distally not quite reaching distal edge of second segment of main flagellum.

Antenna ( Fig. 3D ) with two basal articles fused into wide proximal peduncle article, without apophyses, bearing single inner and outer plumose setae and two inner simple setae; second article just longer than wide; third peduncle article twice as long as second, fourth three-times as long as second. Flagellum of two segments, distal segment with four distal setae.

Labrum ( Fig. 3F ) bilobed, rounded, sparsely setose. Left mandible ( Fig. 3E ) with fine denticulations on outer margin, inner margin finely setose; five rounded denticulations on pars incisiva, robust lacinia mobilis with three rounded denticulations, setiferous lobe with four variously crenulate setae, pars molaris (not figured) round, blunt, corrugated; palp of three articles, proximal article with long, plumose inner seta and row of fine denticulations; second article longest, twice as long as proximal article, with five shorter and five longer inner setae in two rows; third article just longer than first, with six progressively longer setae in distal half, two distal setae much longer than article. Right mandible as left but without lacinia mobilis. Labium ( Fig. 3G ) marginally denticulate, palp with two distal setae. Maxillule ( Fig. 3H ) inner endite with four simple distal setae, outer endite with nine distal spines, outer margins sparsely setose; palp of two articles, distally with four simple setae. Maxilla damaged in preparation, with rostral row of about 20 simple setae, fixed endite with trifurcate, simple and bifurcate setal groups. Maxilliped ( Fig. 3J ) basis with two inner plumose setae; proximal palp article with two spine-like apophyses on outer margin, distal apophysis with plumose seta, distal margin with two plumose setae, inner margin with one plumose seta; second article with proximal apophyses and three plumose setae on outer margin, three plumose setae along inner margin and plumose and simple setae on inner-distal expansion; third article with eight simple setae on inner-distal expansion; distal article with five finely-denticulate inner-marginal setae, single distal and paired outer subdistal setae all plumose along their basal half; endite (not figured) with finely setose outer margin, row of simple linguiform distal spines becoming shorter towards inner margin, two subdistal plumose setae, three coupling-hooks. Epignath ( Fig. 3I ) large, inner lobes conspicuous, margins and distal spine finely setose.

Chelipeds ( Fig. 4A ) with compact basis 1.45 times as long as wide, with two fine dorsoproximal spines, proximal, medial and distal ventral marginal spines and ventrodistal plumose seta; exopodite absent. Merus subrectangular, with ventrodistal spine-like apophysis, single ventral plumose seta and inner row of plumose setae. Carpus elongate, 2.7 times as long as wide, widening distally, with mid-ventral spinelike apophysis, sparse marginal setae, and group of three more robust plumose setae dorsoproximally. Propodus slender, 1.5 times as long as wide, setose as figured; fixed finger with row of small rounded “teeth” interspersed with fine setules on cutting edge; moveable finger (dactylus) slender. Left cheliped marginally more robust than right.

Pereopod 1 ( Fig. 4C ) longest, with stout basis 1.9 times as long as wide, dorsal margin bearing 13 plumose setae but no apophyses, ventral margin with three proximal and one distal simple setae; exopodite present ( Fig. 4D ), large, distal article with 14 plumose setae. Ischium one-quarter as long as basis, with two simple ventral setae.Merus 0.8 times as long as basis, with paired dorsodistal simple setae, ventral margin with five plumose and numerous simple setae. Carpus just shorter than merus, with ventral and distal simple setae. Propodus 1.4 times as long as carpus, with three ventral spines, sparse dorsal setae, three ventrodistal setae one of which twice as long as other two. Dactylus curved, almost as long as propodus, with fine ventral setae, unguis slender, sharp, 0.4 times as long as dactylus.

Pereopods 2 to 6 similar to each other, progressively shorter, each about one-half to one-third as long as pereopod 1; merus, carpus and propodus bearing “sucker-like” spines, generally in three ventral rows. Pereopod 2 ( Fig. 4E ) basis stout, 1.6 times as long as wide, with plumose ventrodistal seta; ischium with four ventrodistal plumose setae; merus 1.7 times as long as carpus, with single dorsal and ventral distal plumose setae; propodus 1.2 times as long as carpus with dorsal penicillate seta and two distal simple setae; dactylus and unguis appearing fused into hook-like claw. Pereopod 3 as pereopod 2, but ischium with only two plumose setae, carpus 1.6 times as long as merus.

Pereopod 4 ( Fig. 4F ) basis 1.5 times as long as wide, with three dorsal plumose setae, ventrodistal plumose seta and shorter simple seta; ischium with three ventrodistal setae; carpus 1.3 times as long as merus with two ventral plumose setae; propodus one-third as long as carpus. Pereopod 5 as pereopod 4 but with plumose setae on ventral margin of basis, penicillate seta mid-dorsally on basis. Pereopod 6 ( Fig. 4G ) basis with three plumose ventral setae and one submarginal dorsal plumose seta; merus and carpus with one and four dorsal plumose setae respectively; propodus with two slender distal spines.

Pleopods ( Fig. 4H ) only present on pleonites 1 and 2, biramous, basis with three ventral plumose setae; exopod with nine plumose setae, endopod with naked dorsal margin and six plumose setae.

Uropod ( Fig. 4I ) biramous, basis with one simple and one plumose outer setae and fine dorsodistal seta; endopod longer than basis, of three segments increasing in length, first and second segments with one and two distal setae respectively, third segment with three robust distal setae and one penicillate seta; exopod nearly as long as proximal two segments of endopod, of two segments subequal in length with two distal setae.

Male closely similar to female, chelipeds significantly dimorphic, one being much larger than the other ( Fig. 4B ); of six males with two attributable chelipeds each, four had the right cheliped larger, two the left. Smaller cheliped substantially similar to that of female. Larger cheliped ( Fig. 4B ) merus with two robust, plumose setae adjacent to ventral apophysis; carpus only 1.7 times as long as wide, with spine-like apophysis subdistally on dorsal margin; propodus massive, 1.5 times as long as carpus, with numerous distal simple setae as figured, fixed finger with blade-like cutting edge, dactylus with spinules along cutting edge.

REMARKS

Within the Pagurapseudinae , the features of pronounced cheliped dimorphism in the male, conspicuous epistome exceeding anterior margin of cephalothorax, the basis of pereopod 1 conspicuously wider than subsequent articles, large plumose setae on the maxilliped palp, and robust distal setae or spines on the uropod endopod are all characteristic of the genus Macrolabrum (see Guţu 1997; Bamber 2007).

Of the seven species of Macrolabrum described previously (see Guţu 1997; Bamber 2005, 2007), only three ( M. distonyx Bamber, 2007 , M. rugosus Guţu, 1997 and M. trichopteroides Băcescu, 1976 ) show fusion of the basal peduncle articles of the antenna, but the last two of these both have a twosegmented endopod and one-segmented exopod to the uropod, while M. rugosus is without pleopods. Macrolabrum distonyx , from deep water off New Caledonia, has a three-segmented endopod and two-segmented exopod to the uropod, but that species has a triangular, denticulate rostrum, only two segments in the main flagellum of the antennule, much shorter antennal articles, less setation of the mandibular palps and pleopods, a more robust smaller cheliped and more denticulations on the outer margin of the maxilliped palp, inter alia.

No other species of Macrolabrum has the form of rostrum shown by M. mansoris n. sp., or three segments in the main flagellum of the antennule.

Figures

FIG. 3. — Macrolabrum mansoris n. sp.: A, cephalothorax and pereonites 1 and 2, dorsal; B, pleonite 5 and pleotelson, dorsal; C, antennule; D, antenna; E, left mandible; F, labrum and epistome; G, labium; H, maxillule; I, epignath; J, maxilliped. Scale bar: A, B, 0.6 mm; C, D, 0.3 mm; E-J, 0.2 mm.

FIG. 4.— Macrolabrum mansoris n.sp.:A, female cheliped;B, male cheliped;C, pereopod 1; D, exopodite of pereopod 1; E, pereopod 2; F, pereopod 4; G. pereopod 6; H, pleopod; I, uropod, ventral. Scale bar: A-C, 0.4 mm; D-I, 0.2 mm.