Tridentella brandtae, 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 : 53-58

Tridentella brandtae sp. nov.

( Figs 9–11 )

Material examined. Holotype: ď (10.5, slightly damaged), Indonesia, Banda Sea, Kei Is, 05°26’S, 132°38’E, 24 October 1991, stn. DW13, 417– 425 m, Baruna Jaya 1 ( MNHN Is.5988).

Paratypes: ď (9.4 mm), Ψ (ovig. 11.8 mm), same data as holotype ( MNHN Is.5989).

Description: Body 2.6 times as long as greatest width, dorsal surfaces polished in appearance, widest at pereonite 5, lateral margins subparallel. Rostral point absent. Eyes separated by about 40% width of head, each eye made up of ~8 transverse rows of ommatidia, each row with ~6–8 ommatidia, eye colour black. Pereon without transverse impressed line on pereonites; pereonite 1 and coxae 2–3 each with posteroventral angle rounded; coxae 5–7 with entire oblique carina; posterior margins of pereonites 5–7 with irregular, weak submarginal nodules. Pleon with pleonite 1 visible in dorsal view; 3–5 posterior margin with irregular small nodules; 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 not extending beyond posterior margin of pleonite 5, rounded. Pleotelson 0.7 as long as anterior width, dorsal surface without longitudinal carinae; surface weakly nodular; posterior margin weakly crenulate, posterior margin sub-truncate, without median point, without RS.

Antennule peduncle articles 1 and 2 distinct, articulated; article 2 0.7 as long as article 1, posterodistal angle not produced; articles 3 and 4 1.4 times as long as combined lengths of articles 1 and 2; article 3 4.8 times as long as wide, posterodistal angle not produced; flagellum with 11 articles, extending to anterior of pereonite 1. Antenna peduncle article 4 2.4 times as long as wide, 2.6 times as long as article 3, inferior margin with 0 plumose setae, and 0 short simple setae; article 5 1.2 times as long as article 4, 3.0 times as long as wide, inferior margin with 0 pappose setae, anterodistal angle with cluster of 2 short simple setae (distal margin with 3 pappose setae); extending to posterior of pereonite 3.

Frontal lamina pentagonal, longer than greatest width, lateral margins concave, anterior margins concave, anterior margin forming median point. Mandible incisor biscuspid; molar process with abundant setae (with marginal spines); palp article 2 with 24 distolateral setae, article 3 with 19 RS. Maxillule with 5 terminal RS (and 4 small sub-terminal RS). Maxilla distomesial margin with 3 serrated scales. Maxilliped palp article 2 mesial margin with 1 slender seta, lateral margin distally with 0 slender setae, article 3 mesial margin with 2 slender setae, lateral margin with 1 slender seta, article 4 mesial margin with 6 slender setae, lateral margin with 4 slender setae, article 5 distomesial margin with 5 setae, lateral margin with 2 setae; endite extending beyond distal margin of palp article 3, with 0 long circumplumose setae.

Pereopod 1 basis 2.5 times as long as greatest width, superior distal angle with cluster of 0 acute simple setae; ischium 0.6 as long as basis, inferior margin with 0 setae, superior distal margin with 1 RS; merus inferior margin with 3 RS (stout molariform), set as single row, superior distal angle with 2 setae; carpus inferior margin with 2 RS (minute; and 1 slender seta); propodus 1.7 times as long as wide, inferior margin with 4 RS (small, large RS opposing base of dactylus); propodal palm weakly concave; dactylus 0.6 as long as propodus. Pereopod 2 more slender than pereopod 1; ischium inferior margin with 5 stout RS (3 minute, 2 large), superior distal margin with 1 RS; merus inferior margin with 4 stout RS, set as two groups, superior distal margin with 2 acute RS; carpus inferodistal angle with 1 RS (large, blunt; about as long as carpus inferior margin). Pereopod 2 propodal palm 13 RS (in two rows of 8 marginal and 5 submarginal). Pereopod 3 similar to pereopod 2. Pereopod 6 similar to pereopod 7. Pereopod 7 basis 2.2 times as long as greatest width, superior margin strongly convex, inferior margin with 3 palmate setae (or more); ischium 0.7 as long as basis, inferior margin with 4 RS, superior distal angle with 4 RS, inferior distal angle with 4 RS; merus 0.5 as long as ischium, 1.4 times as long as wide, inferior margin with 3 RS, superior distal angle with 6 RS, inferior distal angle with 5 RS; carpus 0.4 as long as ischium, 1.1 times as long as wide, inferior margin with 1 RS, superior distal angle with 18 RS, inferior distal angle with 6 RS; propodus 0.5 as long as ischium, 2.4 times as long as wide, inferior margin with 6 RS (set as 1, 1, 2 and 2, increasing in size distally), superior distal angle with 2 slender setae, inferior distal angle with 3 RS.

Penes flat articulating lobes, penial openings separated by 5% of sternal width, penial process 2.7 times as long as basal width.

Pleopod 1 exopod 1.7 times as long as wide, lateral margin weakly convex, distally broadly rounded, mesial margin strongly convex, with PMS from distal one-third, with ~36 PMS; endopod 1.6 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 ~18 PMS; peduncle 2.3 times as wide as long; mesial margin with 4 coupling hooks. Pleopod 2 appendix masculina basally widest, 1.0 times as long as endopod, distally narrowly rounded (with apical 'nipple'). Pleopods 2–5 peduncle distolateral margin with small acute RS, pleopods 3–5 endopods without distomesial serrate scales.

Uropod peduncle ventrolateral margin with 0 RS, lateral margin without medial short acute RS, posterior lobe about one-half as long as endopod; rami not extending beyond pleotelson, marginal setae in single tier, apices narrowly rounded. Endopod apically shallowly bifid; lateral margin weakly convex; distal lateral margin without RS, mesial margin weakly convex, with 3 RS. Exopod not extending to end of endopod, 2.5 times as long as greatest width, apically shallowly and equally bifid; lateral margin weakly convex, without RS; mesial margin straight, distally convex, with 1 RS.

Female: Similar to males, but lack the large robust seta at the inferodistal angle of the carpus of pereopods 2 and 3; the posterior pereopods seem less robust than in the male.

Size: Approximately 9 to 12 mm.

Variation: Robust setae: pleotelson always without RS. Uropod exopod mesial margin with 1 RS (all), lateral margin without RS. Uropod endopod mesial margin with 2–4 RS, with 2 RS most frequent (3 times) and 4 occurring once on the smallest specimen; lateral margin without RS.

Pereopods 2 and 3: Male pereopods 2 and 3 with prominent, blunt robust seta and inferodistal angle of carpus, this being larger in the large male; in the female the robust setae is no larger than the meral robust setae.

Remarks: Tridentella brandtae sp. nov. can be identified by the largely unornamented dorsal surfaces, the posterior margins of pereonites 5 and 6 and of pleonites 3–5 having very weak nodules; the dorsal surface of the pleotelson has very weakly developed low nodules (only just visible in lateral view); the pleotelson posterior margin is subtruncate, weakly medially indented and lacking a medial point; the inferior margin of the propodus of pereopods 2 and 3 with a double row of robust setae; and uropods with even margins, weakly bifid and rounded apices, rami without robust setae on the lateral margins, and only one robust seta on the mesial margin of the exopod, 2–4 robust setae on the mesial margin of the endopod. Males are further characterised by the presence of a large bluntly rounded robust seta at the inferodistal angle of the carpus.

The only similar species is the briefly described Tridentella japonica Thielemann, 1910 . Thielemann’s description and figures are of insufficient detail to allow comparisons between the two species, and the collections holding the types are believed to have been destroyed in World War II (O. Coleman, personal communication). Apparent differences between the two species are, in T. japonica , the clypeus being relatively long (vs a thin band in T. brandtae ), the uropodal endopod posterior margin straight (vs convex). Other potential differences cannot be assessed, but if the drawings are accurate a further difference would be the lack of weak dorsal nodules on T. japonica . Without a redescription from the type material T. japonica can only be considered as nomen dubium.

Distribution: Banda Sea, Indonesia; depth of 417–425 metres.

Etymology: Named in honour of Professor Angelika Brandt, recognising her great contribution to knowledge of the marine Isopoda .

Figures

FIGURE 9. Tridentella brandtae sp. nov. B – G, holotype; A, H, I, male paratype. A, dorsal view; B, lateral view; C, frons; D, head; E, pleonites, lateral view; F, pleotelson, posterior margin; G, sternite 7 showing penial processes; H, antennule; I, antenna peduncle.

FIGURE 10. Tridentella brandtae sp. nov. A – G, male paratype; H and I, holotype. A, mandible; B, molar process margin; C, maxilla; D, maxilla apex; E, maxillule apex; F, maxilliped; G, uropod; H, pleopod 1; I pleopod 2.

FIGURE 11. Tridentella brandtae sp. nov. A – E, holotype; F, G, male paratype; H, female paratype. A, pereopod 1; B, pereopod 1, merus inferior margin, ventral view; C, pereopod 2; D, pereopod 7; E, pereopod 7, carpus distal margin; F, pereopod 2; G, pereopod 6, carpus distal margin; H, pereopod 2 female, distal articles.