Metapseudes wilsoni, Błażewicz-Paszkowycz & Bamber, 2007

Błażewicz-Paszkowycz, M. & Bamber, R. N., 2007, New apseudomorph tanaidaceans (Crustacea: Peracarida: Tanaidacea) from eastern Australia: Apseudidae, Whiteleggiidae, Metapseudidae and Pagurapseudidae, Memoirs of Museum Victoria 64, pp. 107-148 : 141-146

Metapseudes wilsoni sp. nov.

Figures 20–23

Material. Ovigerous female, holotype (NVM J23601) Australia, Victoria, eastern Bass Strait, 11.2 km E of eastern edge of Lake Tyers (37°51.25'S, 148°13.10'E), 32 m, 25/09/1990, (MSL-EG 27), Marine Science Laboratories. Paratypes: 117 specimens including males and ovigerous females (NVM J55751), 2 dissected on slides (NVM J55939); same locality as holotype.

Description of female. Body not particularly dorsoventrally flattened, holotype 2 mm long (tip of rostrum to posterior of pleotelson), 4.9 times as long as wide. Cephalothorax subrectangular, 1.35 times as long as wide, naked; anterior margin with conspicuous square rostrum. Eyelobes and eyes present, with black pigment. 6 free pereonites, lateral margins uniformly convex, with paired anterolateral setae on each side; pereonites 1 and 2 subequal, about one-third as long as cephalothorax; pereonite 3 longest, 1.25 times as long as pereonite 1; pereonites 4 and 5 slightly shorter, pereonite 6 shortest, 0.8 times as long as pereonite 1 (all pereonites respectively 2.2, 2.3, 1.8, 2.0, 2.0 and 2.5 times as wide as long). Pleon twice as long as pereonite 5, of 5 free subequal pleonites bearing pleopods plus pleotelson; pleonites some 9 times as wide as long, not laterally expanded, with paired dorsolateral and lateral setae. Pleotelson 0.75 times as long as wide, as long as pereonite 5, with single midlateral, subdistal and distal marginal setae on each side, and pair of middorsolateral setae.

Antennule peduncle article 1 stout, 3 times as long as wide, with conspicuous denticulations along inner and outer margins, outer margin with longer subdistal seta and groups of proximal, mesial and distal penicillate setae; inner margin with 2 simple setae in distal one-third; peduncle article 2 0.3 times as long as article 1, with inner proximal denticulations, inner, dorsal and outer distal setae, and outer distal group of penicillate setae; article 3 one-quater length of article 1, article 4 one-fifth as long as 2nd, with inner distal seta. Main flagellum of 2 segments, proximal segment with 3 simple distal setae, distal segment with 2 longer distal setae, 1 shorter subdistal seta and 2 aesthetascs; accessory flagellum of 2 segments.

Antenna peduncle article 1 with denticulate inner margin; article 2 distally denticulate on inner margin, naked, 0.7 times length of article 1; peduncle article 3 as long as article 2, with 1 inner distal penicillate seta; article 4 just longer than article 3, with 2 distal penicillate setae. Flagellum of 2 segments, distal segment with 2 shorter and 1 longer distal setae. Squama absent.

Mouth parts. Labrum not seen. Left mandible with narrow crenulated pars incisiva, lacinia mobilis as long as pars incisiva and distally crenulate, setiferous lobe with 4 simple setae, pars molaris elongate, stout, blunt with spinose extension at dorsal rim; mandibular palp of 3 articles, article 1 naked, article 2 as long as article 1 with dorsodistal seta, article 3 half as long as article 2 with 3 shorter and 1 longer distal setae, the longer as long as article 2. Right mandible as left. Maxillule inner endite with 4 setulate distal setae; outer endite with 9 distal spines, 2 shorter than the rest, outer margin finely setose; palp of 2 articles, article 2 one-third length of 1st and with 2 distal setae. Maxilla outer lobe of moveable endite with 2 subdistal and 4 distal simple setae; inner lobe of moveable endite distally with 7 simple setae; outer lobe of fixed endite distally with 3 simple outer setae and 3 trifurcate inner setae, subdistally with setulose seta; inner lobe of fixed endite with rostral row of 13 setae guarding 2 longer plumose setae. Labium with denticulate outer margin, palp elongate, with paired outer setae, fine distal setules and single distal spine. Maxilliped basis with simple inner distal seta; palp article 1 with outer distal spine on apophysis and single inner distal setulose seta; palp article 2 longer than wide, with sparse row of 6 simple and 2 setulose setae on inner margin, stout outer distal seta; palp article 3 0.6 times as long as wide, with 4 simple stout setae on inner distal margin; palp article 4 with 7 distallydenticulate distal setae. Endite with setulose distal and outer marginal setae, inner margin with fine setules, and 4 coupling hooks. Epignath elongate cup-shaped, with setulose distal spine.

Cheliped robust, basis as long as wide with small ventrodistal seta; exopodite absent. Merus subrectangular, ventrodistal shoulder with single seta. Carpus twice as long as wide, with simple dorsodistal seta, midventrally with paired simple setae among slight marginal crenulations. Chela fingers shorter than palm; palm with paired distal setae at articulation of dactylus; fixed finger with 3 ventral setae, cutting edge with sparse setae; dactylus with 3 distal setae, distal claw pointed.

Pereopods generally all somewhat similar.

Pereopod 1 basis compact, 2.7 times as long as wide, with simple setae and 2 triangular apophyses along dorsal margin, 2 fine setae on ventral margin; exopodite absent. Ischium naked. Merus 0.4 times as long as basis, with long inner distal seta and 1 outer distal spine. Carpus 0.8 times as long as merus, with 3 ventral spines, 2 dorsodistal spines and 3 distal simple setae. Propodus as long as merus, with 4 ventral spines, 2 stout dorsodistal spines, dorsodistal and ventrodistal simple setae, and mid-dorsal penicillate seta. Dactylus stout, with fine midventral denticulation; unguis short, slender, one-third length of dactylus.

Pereopod 2 similar to but more slender than pereopod 1, basis 3 times as long as wide, dorsally with single triangular apophysis, ischium with single ventrodistal seta, merus with single ventrodistal and dorsodistal setae, carpus with 5 ventral short spines in 2 rows, and 2 mid-distal short spines; propodus 2.3 times as long as wide, with 4 ventral, 1 mesial and 2 dorsodistal short spines, and 2 fine dorsal and 1 longer dorsodistal setae; dactylus with ventral seta; unguis stout.

Pereopod 3 similar to pereopod 2, but dorsal margin of basis with 2 apophyses; merus dorsodistally naked.

Pereopod 4 similar to pereopod 2, but propodus with mid-dorsal penicillate seta, and dorsodistal tuft of 2 simple and 5 finely denticulate setae, more conspicuous “heel” on dactylus.

Pereopod 5 as pereopod 2 but with dorsodistal spine on merus, fewer spines on carpus and propodus, more conspicuous “heel” on dactylus.

Pereopod 6 similar to pereopod 5, but carpus without spines but with 4 distal simple setae, propodus with distal tuft of 8 finely denticulate setae.

Pleopods all alike. Basis naked, both rami slender, subequal in length, with 2 (exopod) or 3 (endopod) distal setae.

Uropod basis elongate, with 1 longer and 1 shorter outer distal setae. Exopod of 2 segments, endopod of 4 segments, setose as figured.

Male. Generally as female, body shorter (4.6 times as long as wide). Cheliped dimorphic, proportionately larger, carpus 1.6 times as long as wide, chela nearly twice as long as carpus, propodal palm 1.45 times as long as wide, fixed finger excavate to give wide separation from dactylus, cutting edge distally denticulate and setulose; dactylus longer than carpus. Cheliped of subadult male transitional, dactylus cutting edge with proximal rounded apophysis.

Etymology. Named for Dr Robin Wilson of Museum Victoria, who undertook much of the Bass Strait sampling.

Remarks. The only genus of the Metapseudinae without an antennal squama is Metapseudes ; this genus is further distinguished from the others in having a simply setose trunk, no plumose setae on the basis of pereopod 1, and a simple rostrum. The only species previously known from this genus is M. aucklandiae Stephensen, 1927 , described from New Zealand in shallow waters ( Stephensen, 1927), and usefully redescribed from the type and other material by Gardiner (1973) (depth range 0–113 m). The 2 species have similar lateral dentition of the basal 2 articles of the antennule, rostrum, trunk setation, mouthpart morphology, pleopod and uropod morphology, no exopodites on the cheliped or pereopod 1 and, of course, no antennal squama.

The most evident difference between these species is that Metapseudes wilsoni sp. nov. has conspicuously more slender antennules and antennae (proximal antennule peduncle article of M. aucklandiae 1.6 times as long as wide) with more pronounced, pointed denticulations on the proximal antennule peduncle article, and 1 fewer article in the main flagellum of the antennule ( Stephensen, 1927, erroneously showed the 4th peduncle article split as 2 basal flagellar articles), but also 2 (rather than 1) distal setae on the maxillule palp, no indentation in the anterior margin of the rostrum, a more slender cheliped in the female (carpus of M. aucklandiae 1.7 times as long as wide), fewer dorsal apophyses on the pereopod bases, and a more slender pereopod 2 (propodus of M. aucklandiae about 1.2 times as long as wide).