Tridentella tanimbar, Bruce, Niel L, 2008

Bruce, Niel L, 2008, New species of Tridentella Richardson, 1905 (Isopoda: Cymothoida: Tridentellidae), tropical marine isopod crustaceans from the Banda Sea, Indonesia, Zootaxa 1734, pp. 43-58 : 49-53

Tridentella tanimbar sp. nov.

( Figs 5–8 )

Material examined. Holotype: ď (31 mm), Indonesia, Banda Sea, Tanimbar Is, 08°41’S, 131°18’E, 2 November 1991, KARUBAR stn. CP70, 413– 410 m, Baruna Jaya 1 ( MNHN Is.5987).

Description: Body 2.1 times as long as greatest width, dorsal surfaces smooth, sparsely punctate, widest at pereonite 6, lateral margins weakly ovate. Rostral point present, weakly developed. Eyes separated by about 46% width of head, each eye made up of ~16 transverse rows of ommatidia, each row with 7 or 8 ocelli, eye colour pale brown. Pereonites without transverse impressed line; pereonite 1 and coxae 2–3 each with posteroventral angle right-angled; coxae 5–7 with entire oblique carina; posterior margins of pereonites 5–7 smooth. Pleon with pleonite 1 visible in dorsal view; pleonites 3–5 posterior margin smooth; posterolateral angles of pleonite 2 forming acute point, not posteriorly produced; pleonite 3 with posterolateral margins not extending to posterior margin of pleonite 4, acute; clearly extending beyond posterior margin of pleonite 5, posterolateral margin of pleonite 4 acute; pleonite 5 with posterolateral angles overlapped by lateral margins of pleonite 4. Pleotelson 1.2 times as long as anterior width, dorsal surface without longitudinal carinae; surface smooth; lateral margins sinuate, posterior margin smooth, posterior margin with deep notch, with small distinct median point, without RS.

Antennule peduncle articles 1 and 2 distinct, articulated; article 2 1.2 times as long as article 1, posterodistal angle not produced; articles 3 and 4 1.7 times as long as combined lengths of articles 1 and 2; posterodistal angle not produced; flagellum with 32 articles, extending to pereonite 2. Antenna flagellum with 44 articles, extending to pereonite 5 or pereonite 6.

Frontal lamina lateral margins convex, not angled, longer than greatest width, lateral margins converging to anterior, anterior margins convex, anterior margin forming median point. Mandible incisor tricuspid; molar process with abundant setae; palp article 2 with 35–40 distolateral setae, article 3 with ~40 RS. Maxillule with 6 terminal RS (and 5 small sub-terminal RS). Maxilla distomesial margin with 6 serrated scales. Maxilliped palp article 2 mesial margin with 1 slender seta, lateral margin distally with 0 slender setae, article 3 mesial margin with 6 slender setae, lateral margin with 3 slender setae, article 4 mesial margin with 11 slender setae, lateral margin with 7 slender setae, article 5 distomesial margin with 12 setae, lateral margin with 2 setae; endite extending beyond distal margin of palp article 3, with 0 long circumplumose setae (1 small hooked RS).

Pereopod 1 basis 3.1 times as long as greatest width, superior distal angle without; ischium 0.3 as long as basis, inferior margin with 0 setae, superior distal margin with 1 RS; merus inferior margin with 4 RS (very small), set as two groups, superior distal angle with 1 setae; carpus inferior margin with 1 RS; propodus 2.4 times as long as wide, inferior margin with 0 RS; propodal palm weakly concave; dactylus 0.8 as long as propodus. Pereopod 2 more slender that pereopod 1; ischium inferior margin with 1 stout RS, superior distal margin with 1 RS (and 1 slender seta); merus inferior margin with 8 small stout RS, set as two rows, superior distal margin with 1 acute RS (and 1 slender seta); carpus inferodistal angle with 2 RS; propodal palm with 3 RS (minute, acute). Pereopod 3 similar to pereopod 2. Pereopod 6 similar to pereopod 7. Pereopod 7 basis 4.7 times as long as greatest width, superior margin weakly convex, inferior margin with 9 palmate setae; ischium 0.4 as long as basis, inferior margin with 5 RS (set as 1, 1 and 3), superior distal angle with 3 RS, inferior distal angle with 3 RS; merus 1.1 times as long as ischium, 3.4 times as long as wide, inferior margin with 5 RS (set as 1, 2 and 2), superior distal angle with 5 RS, inferior distal angle with 5 RS; carpus 0.9 as long as ischium, 2.9 times as long as wide, inferior margin with 4 RS (set as 1, 1 and 2), superior distal angle with 21 RS, inferior distal angle with 7 RS; propodus 0.8 as long as ischium, 4.8 times as long as wide, inferior margin with 4 RS (set as 1, 1 and 2), superior distal angle with 1 slender seta, inferior distal angle with 3 RS.

Penes flat articulating lobes, penial openings separated by 11% of sternal width, penial process 1.0 times as long as basal width.

Pleopod 1 exopod 1.6 times as long as wide, lateral margin strongly convex, distally broadly rounded, mesial margin strongly convex, with PMS from distal half; endopod 1.9 times as long as wide, distally broadly rounded, lateral margin strongly concave, with PMS from on distal margin only, mesial margin with PMS from distal one-third; peduncle 2.3 times as wide as long; mesial margin with 8 coupling hooks. Pleopod 2 appendix masculina basally widest, 0.8 as long as endopod, distally narrowly rounded. Pleopods 2–5 peduncle distolateral margin with small acute RS.

Uropod peduncle ventrolateral margin with 1 RS, lateral margin without medial short acute RS, posterior lobe about one-third as long as endopod (0.28); rami not extending beyond pleotelson, apices acute. Endopod apically shallowly bifid; lateral margin proximally convex or distally straight, proximal lateral margin with 3– 5 RS; distal lateral margin with 1 or 2 RS, mesial margin weakly convex, with 4 or 5 RS. Exopod not extending to end of endopod, 3.4 times as long as greatest width, apically shallowly and equally bifid; lateral margin weakly sinuate, with 10 RS; mesial margin straight, distally convex, with 3 or 4 RS.

Remarks: Tridentella tanimbar sp. nov. species bears a remarkable similarity to Tridentella recava Bowman, 1986 , on several characters, such as body shape, coxal morphology and the shape of the pleotelson and uropods, and the species can be considered ‘sister species’. The pleotelson is unique within the family in being prominently excavate with the margins forming two acute points on either side of the excavation. The mouthparts and pleopods of the two species are effectively the same and, while differing in details of the robust setae, the overall form of the pereopods and uropods is also the same. Despite this general similarity, T. tanimbar differs from T. recava in numerous details, the most obvious of which are: free lateral margins to pleonite 5 (laterally overlapped by pleonite 4 in T. recava ), more slender pereopods 2 and 3, lack of long slen- der robust setae on the inferior margins of pereopods 1–3, uropods not extending beyond the pleotelson, and a uropod exopod that is shorter than the endopod (0.87) and falls well short of the endopod apex in T. tanimbar compared to about as long (0.95) as the endopod and extends nearly to the endopod apex in T. recava .

Etymology: The epithet is the Indonesian name for the island near the type locality (noun in apposition).

Figures

FIGURE 5. Tridentella tanimbar sp. nov. Holotype. A, dorsal view; B, lateral view; C, head; D, frons; E, pleotelson apex; F,

FIGURE 6. Tridentella tanimbar sp. nov. Holotype. A, mandible; a, seta from molar process; B, maxillule; C, maxillule apex; D, maxilla; E, maxilla apex; F, maxilliped; G, maxilliped palp articles 4 and 5.

FIGURE 7. Tridentella tanimbar sp. nov. Holotype. A, pereopod 1; B, pereopod 1, merus inferior margin; C, pereopod 2;

FIGURE 8. Tridentella tanimbar sp. nov. Holotype. A – C, pleopods 1 – 3 respectively; D, uropod exopod, dorsal view; E, uropod exopod, ventral view; F, uropod endopod apex.