Triaina isodonte, Just, Jean, 2009

Just, Jean, 2009, Triaina, a new genus in the Janirellidae Menzies, 1956 (Crustacea: Isopoda: Asellota), with two new species from south-eastern Australia, and a new diagnosis for the family, Zootaxa 1980, pp. 1-15 : 3-9

Triaina isodonte sp. nov.

Figs 1–4

Type fixation. Holotype, male, here designated. Australian Museum, AM P76939.

Type locality. Tasman Sea, off NE coast of Tasmania.

Material examined. Holotype, male, 7.5 mm (tip of pseudorostrum to apex of pleotelson), east of Swan Island, Tasmania, Australia, 40°45.94'S 149°01.62'E to 40°46.54'S 149°00.27'E, 2400–2500 m, light grey clay and mud, sledge, 10 December 1986, ORV Franklin, stn FR1086-4, Australian Museum, AM P76939.

Paratypes (14 specimens). Same data as holotype, AM P76941 (1 female). Same data as holotype, AM P76940 (2 females, 3 broken specimens). Tasmania, 48 km ENE of Cape Tourville, Freycinet Peninsula, 42°00.25'S 148°43.55'E to 41°57.77'S 148°42.08'E, 1264– 1130 m, gravel, lumps of sandy mud, WHOI epibenthic sled, G.C.B. Poore et al., 30 October 1988, ORV Franklin, stn SLOPE-81, Museum Victoria NMV J18674 (1 pleotelson). Tasmania, 54 km ENE of Cape Tourville, Freycinet Peninsula, 41°57.30'S 148°58.54'E to 41°56.86'S 148°56.97'E, 1770– 1735 m, coarse biogenic sand, WHOI epibenthic sled, G.C.B. Poore et al., 30 October 1988, ORV Franklin, stn SLOPE-82, NMV J18675 (1 juvenile male, 6 broken specimens).

Description. Head approximately 4 times wider than long, frontal margin a low even curve; pseudorostrum with 3 equal sized prongs reaching just beyond article 1 of antennulae; dorsal surface of head with 3 rounded humps, middle one the largest; lateral margins straight, with forward pointing triangular projection.

Pereonites 1–6 of equal width, 7 slightly less wide; 1–4 and 6 of subequal length, 5 and 7 slightly shorter; all pereonites dorsally with 2 transverse grooves, 1–4 with 2 dorsolateral humps each side; lateral margins 1–4 flattened, truncate, 2–4 with small incision, smallest and most anteriorly in 2; pereonite 5 anterolateral margins with deeper, narrow incision, anterior lobe acute, posterior lobe broad, laterally truncate; pereonites 6–7 similar to 5, but without incision. Pereonite 7 with mid-ventral pointed, posteriorly curved spine.

Pleotelson nearly as wide as pereonite 7, as long as pereonites 1 and 2 combined; lateral margins convex in proximal half, concave distally merging into projecting bifid corners; entire lateral margins and projections irregularly serrate; posterior projection broadly rounded, margin smooth, reaching beyond lateral corners by half its length.

Antennula of 9 articles, reaching to half length of antenna article 5, article 4 distinctly shorter than 3 and 5, 6–9 with single aestetasc. Antenna as long as head, pereonites 1–5 and half of 6 combined, flagellum of approximately 40 articles (41 in Fig. 1 cd); entire antenna with a few short simple setae.

Mouthparts. Upper lip rounded, asymmetrically notched apically. Mandible: lacinia mobilis of left mandible about as strong as incisor, with similar dentition; setal row on both side of approximately 10 setae, distal ones broad, serrate; palp articles 1 and 2 of subequal length, 2 with long hemiplumose setae distally, 2 and 3 with many cuticular combs on surface, 3 with dense row of stiff setae on concave margin. Lower lip with large rounded outer lobes set at 45° angle to midline; inner lobes small, rounded, adpressed in midline. Maxilla 1 outer plate with 12 strong setae, all but distalmost 2–3 serrate, lateral margin with tufts of fine setules in middle; inner plate with two short robust setae on apex surrounded by simple setae, lateral margin with scattered long setules. Maxilla 2 outer and middle lobes subequal, slender, curved; inner lobe broader, shorter, with rounded apex; outer lobe with 4 pectinate setae apically, lateral and medial margins with simple setae and setules; middle lobe apex as outer lobe, distal half of medial margin with dense row of stiff sharply pointed, microdentate setae; inner lobe with numerous simple setae distally, a single long hemiplumose seta on medial margin and many long setules more proximally. Maxilliped, epipod tapering distally, reaching to base of palp article 4, heavily covered with cuticular ridging, margins with fine setules; apex of endite concave with row of 5 broad fan-shaped setae surrounded by simpler setae; palp article 2 with cover of fine setules on ventrolateral surface.

Pereopod I shorter and more robust than succeeding legs; basis length 2.7 width; ischium expanded distally, 0.65 length of basis; merus 0.4 length of ischium, with short anterodistal triangular projection; carpus length 2.7 width, slightly tapering distally, posterior margin with row of 6 robust setae; propodus 0.6 length of carpus, with 4 robust setae along posterior margin; dactylus 0.7 length of propodus, main claw 0.4 length of dactylar body. Pereopods II–VII identical walking legs; basis length approximately 5 times width; ischium expanded dorsally in middle, length 0.54–0.60 length of basis; merus more slender than in pereopod I but of similar shape; carpus with parallel sides, length approximately 4 times width, with posterior row of short robust setae; propodus more slender than carpus, about 0.9 length of carpus, with posterior row of short robust setae; dactylus 0.4 length of propodus, main claw 0.4 length of dactylar body.

Male. Pleopod I length 3.2 proximal width, lateral margins straight, slightly tapering, apical lobes evenly rounded without corners, with dense fringe of simple setae; stylet guide groove opening distolaterally. Pleopod II protopod acutely pointed; stylet in retracted position reaching to tip of protopod, slightly curved. Pleopod III endopod subrectangular, part of lateral, distal and medial margins with dense cover of fine setules, apically with 3 plumose setae; exopod free part about half length of endopod, acutely pointed, lateral margin and distal half of medial margins fringed with long setules, apex with single simple seta. Pleopod IV exopod narrowly ovoid with pointed apex, as long as endopod, proximal 2/3 of lateral margin with fringe of long setules, apex with long plumose seta; endopod broadly oval, with a few tiny setules on apex. Pleopod V similar to but slightly larger than endopod pleopod IV, without apical setules. Female operculum ovoid, apex rounded.

Uropods not reaching apex of pleotelson posterior projection, ramus approximately twice length of protopod, with apical tuft of simple and penicillate setae.

Distribution. Eastern Tasmania, Australia, 1130–2500 m.

Remarks. Triaina isodonte sp. nov. differs from its only known congener, T. makridonte sp. nov. (see below), primarily by having all three prongs of the pseudorostrum of equal size (middle prong much longer than the two side prongs in T. makridonte ) and by having incisions in the lateral margin of pereonites 2–5 (lateral margins entire).

Etymology. The species name is composed of the Greek ɩσος (isos) meaning equal and δόνɩ (donte) meaning tooth, alluding to the near equal size of the three pseudorostral prongs.

Figures

FIGURE 1. Triaina isodonte sp. nov. Holotype, male. Lateral and dorsal views. an, antenna articles 1 – 4 with antennal scale; au, antennula; cd, dorsal view of head with antennula and antenna; co, oblique anterolateral view of head, antennula and antenna insertions indicated by hatching; cv, ventral view of head; up, uropod. Scale bar for both habitus illustrations: 1 mm.

FIGURE 2. Triaina isodonte sp. nov. Holotype, male. ll, lower lip; md r, right mandible; mx 1 and mx 2, maxilla 1 and 2; mxp, maxilliped.

FIGURE 3. Triaina isodonte sp. nov. Holotype, male, except F, female paratype. op, female operculum in situ, oblique view; pl 1 – pl 5, pleopods I – V; pt 1, ventral view of pleon with pleopods in place; pt 2, ventral view of pleon with pleopods removed, exposing anus.

FIGURE 4. Triaina isodonte sp. nov. Holotype, male. 1 – 7, pereopods I – VII.