Tridentella palmata, Bruce & Svavarsson, 2018

Bruce, Niel L. & Svavarsson, Jörundur, 2018, Three new species of Tridentella Richardson, 1905 (Isopoda: Cymothoida: Tridentellidae) from New Caledonia, Zootaxa 4399 (1), pp. 101-118 : 103-108

Tridentella palmata sp. nov. Figs 1–5

Material examined. All New Caledonia. Holotype: ♂ (5.9 mm), Iles, Loyaute, Lifou, Baie du Santal, 20°47.35’S, 167°05.70’E, 13 February 1989, MUSORSTOM VI, stn DW391, 340– 390 m, N.O.“ Alis ”, Bouchet, Métivier & Richer de Forges-IRD coll. (MNHN-IU-2017-17).

Paratypes: ♀ (ovig. 6.0 mm), Grand Passage, 19°04.0’S, 163°27.5’E, 18 September 1985, MUSORSTOM V, IV stn DW184, N.O. “ Vauban ”, 260 m, Bouchet & Richer de Forges-IRD coll. (MNHN-IU- 2017-18). ♀ (non-ovig. 7.0 mm, dissected), Côte est, 24°00.00’S, 166°35.710’E, 19 March 1999, BATHUS I, N.O.“Alis”, 315–327 m, Bouchet & Richer de Forges-IRD coll. (MNHN-IU- 2017-19).

Description: Body 2.5 times as long as greatest width, dorsal surfaces smooth, widest at pereonites 5 and 6, lateral margins weakly ovate. Head smooth, without ornamentation, rostral point absent. Eyes separated by about 20% width of head, each eye made up of ~9 transverse rows of ommatidia, each row with ~6–7 ommatidia, eye colour black. Pereon with transverse impressed line absent on pereonites 3–5; pereonite 1 and coxae 2–3 each with posteroventral angle right-angled (coxae 2 rather rounded); coxae 5–7 with incomplete oblique carina; posterior margins of pereonites 5–7 smooth. Pleon with pleonite 1 visible in dorsal view; pleonites 3–5 posterior margin smooth, flexed laterally; posterolateral angles of pleonite 2 forming acute point, not posteriorly produced; pleonite 3 with posterolateral margins not extending to posterior margin of pleonite 5, narrowly rounded; posterolateral margins of pleonite 4 clearly extending beyond posterior margin of pleonite 5, narrowly rounded. Pleotelson 0.6 times as long as anterior width, dorsal surface with paired submedian longitudinal carina (broad, very weak); surface smooth; lateral margins weakly convex, smooth; posterior margin weakly crenulate, posterior margin subtruncate, without median point, with 0 RS.

Antennula peduncle articles 1 and 2 distinct, articulated; article 2 0.9 times as long as article 1, posterodistal angle not produced; articles 3 and 4 1.2 times as long as combined lengths of articles 1 and 2; article 3 3.8 times as long as wide, posterodistal angle not produced; flagellum with 9 articles, extending to anterior of pereonite 1. Antenna peduncle article 4 1.7 times as long as wide, 1.5 times as long as article 3, inferior margin with 0 plumose setae, and 1 short simple setae; article 5 1.9 times as long as article 4, 2.4 times as long as wide, inferior margin with 0 pappose setae, anterodistal angle with cluster of 3 short simple setae; extending to posterior of pereonite 1.

Frontal lamina complex, 4.4 times as long as basal width, posterior two-thirds subparallel, then expanding abruptly, anterior margin subtruncate with distinct median point; longer than greatest width, lateral margins diverging strongly and abruptly towards anterior. Mandible incisor weakly tricuspid; molar process with abundant setae; palp article 2 with 7 distolateral setae, article 3 with 12 RS. Maxillula with 2 terminal low, rounded RS. Maxilla distomesial margin with 3 serrated scales. Maxilliped palp article 2 mesial margin with 1 slender setae, lateral margin distally with 0 slender setae, article 3 mesial margin with 2 slender setae, lateral margin with 0 slender setae, article 4 mesial margin with 3 slender setae, lateral margin with 1 slender setae, article 5 distomesial margin with 5 setae, lateral margin with 2 setae; endite extending beyond distal margin of palp article 3, with 3 long circumplumose setae.

Pereopod 1 basis 2.7 times as long as greatest width, superior distal angle with cluster of 0 acute simple setae; ischium 0.4 times as long as basis, inferior margin with 6 setae, superior distal margin with 2 RS; merus inferior margin with 5 RS (bluntly rounded), set as single row, superior distal angle with 2 setae; carpus inferior margin with 1 RS; propodus 1.9 times as long as wide, inferior margin with 2 RS; propodal palm weakly concave; dactylus 0.6 times as long as propodus. Pereopod 2 more slender than pereopod 1. Pereopod 2 ischium inferior margin with 4 stout RS, superior distal margin with 2 RS; merus inferior margin with 6 stout RS, set as two groups, superior distal margin with 2 acute RS; carpus inferodistal angle with 2 RS. Pereopod 2 propodal palm with 2 RS (third large RS opposing base of dactylus). Pereopod 3 similar to pereopod 2 (robust setae at base of dactylus larger than for pereopod 2). Pereopod 4 carpus with with 12 large RS; prododus with one large and 2 small RS large setae, dactylus elongate 2.4 times as long as propodus, 7.0 times as long as basal width, tip extending to carpus). Pereopod 6 similar to pereopod 7. Pereopod 7 basis 2.4 times as long as greatest width, superior margin convex, inferior margin with 5 palmate setae; ischium 0.6 as long as basis, inferior margin with 3 RS (two groups), superior distal angle with 1 RS, inferior distal angle with 3 RS; merus 0.8 as long as ischium, 1.4 times as long as wide, inferior margin with 2 RS, superior distal angle with 5 RS, inferior distal angle with 5 RS; carpus 0.7 as long as ischium, 1.4 times as long as wide, inferior margin with 2 RS, superior distal angle with 6 RS, inferior distal angle with 8 RS; propodus 1.1 as long as ischium, 2.5 times as long as wide, inferior margin with 2 RS, superior distal angle with 3 slender setae (+ 1 RS), inferior distal angle with 3 RS.

Penes flat articulating lobes, penial process 0.7 times as long as basal width.

Pleopod 1 exopod 1.6 times as long as wide, lateral margin weakly convex, distally broadly rounded, mesial margin straight, with PMS from distal one-third, with ~27 PMS; endopod 1.5 times as long as wide, distally broadly rounded, lateral margin straight, with PMS on distal margin only, mesial margin with PMS on distal margin only, endopod with ~11 PMS; peduncle 2.8 times as wide as long; mesial margin with 4 coupling hooks. Pleopod 2 exopod with ~ 33 PMS, endopod with ~ 15 PMS; appendix masculina basally swollen, 1.1 times as long as endopod, distally acute.

Uropod peduncle lateral margin without medial short acute robust seta, uropod peduncle posterior lobe about one-third as long as endopod; rami extending beyond pleotelson, marginal setae in single tier, apices broadly rounded. Endopod apically not bifid; lateral margin weakly convex, proximal lateral margin with 0 RS; distal lateral margin with 0 RS, mesial margin strongly convex, with 0 RS. Exopod not extending to end of endopod, 2 times as long as greatest width, apically not bifid; lateral margin weakly convex, with 0 RS; mesial margin convex, with 0 RS.

Female: Not known.

Size: 5.9–7.0 mm.

Remarks: Tridentella palmata sp. nov., while lacking obvious dorsal ornamentation that is present in several species is nonetheless a highly distinctive species. The eyes are large for the family, but the remarkably robust and heavily “spinose” pereopod 4, with an exceptionally elongate dactylus makes for ready identification. There are no evidently similar species, although Tridentella saxicola ( Hale, 1925) has a similar body form, pleotelson and uropods.

Etymology: From the Latin palm (inside of hand), alluding to the robust seta and long dactylus on pereopod 4.

Figures

FIGURE 1. Tridentella palmata sp. nov., A–C, E–J, holotype male (5.9 mm, MNHN-IU-2017-17); D, female paratype (7.0 mm, MNHN-IU-2017-19). A, habitus, dorsal view; B, posterior pereonites, dorsal view; C, habitus, lateral view; D, habitus, dorsal view; E, head, dorsal view; F, frons; G, pleonites; H, pleotelson and uropods; I, posterior margin of pleotelson; J, penial process.

FIGURE2. Tridentella palmata sp. nov., A–B, holotype male (5.9 mm, MNHN-IU-2017-17); C–F, female paratype (7.0 mm, MNHN-IU-2017-19).A, antennula (in situ), B,antenna (in situ); C, mandible; D, maxillula; E, maxilla, F, maxilliped.

FIGURE3. Tridentella palmata sp. nov., A–B, holotype male (5.9 mm, MNHN-IU-2017-17); C–F, female paratype (7.0 mm, MNHN-IU-2017-19). A, pereopod 1; merus–dactylus of pereopod 1, mesial view; C, pereopod 1; D, carpus–dactylus of pereopod 1;E, pereopod 2; F, pereopod 3.

FIGURE 4. Tridentella palmata sp. nov., female paratype (7.0 mm, MNHN-IU-2017-19). A, pereopod 4; B, carpus–dactylus of pereopod 4; C, carpus–dactylus of pereopod 4, ventral view, in situ; D, carpus–dactylus of pereopod 1, ventral view, in situ; E, pereopod 6; F, pereopod 7.

FIGURE 5. Tridentella palmata sp. nov., A–B, holotype male (5.9 mm, MNHN-IU-2017-19); C, female paratype (7.0 mm, MNHN-IU-2017-19).A, pleopod 1; B,pleopod 2; C, uropod.