Tridentella memikat, 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 : 44-49

Tridentella memikat sp. nov.

( Figs 1–4 )

Material examined. All material Kei Is., Banda Sea, Indonesia; coll. KARUBAR expedition.

Holotype: ď (32 mm), 07°40’S, 132°27’E, 28 October 1991, stn. CP38, 620– 666 m, Baruna Jaya 1 ( MNHN Is.5983).

Paratypes: ď (18.0 mm, immature), 3 Ψ (non-ovig. 18.0, 18.5 [mouth dissection], 27 [uropod] mm), 3 mancas (14.0, 15.0, 15.5 mm), 3 pre-mancas (10.8, 11.0, 11.2 mm), same data as holotype ( MNHN Is.5984). ď (33 mm, damaged [main dissection]), 4 Ψ (non-ovig. 20, 24, 29, 40 mm), 05°15’S, 132°59’E, 25 October 1991, stn. CP20, 769– 809 m, Baruna Jaya 1 ( MNHN Is.5985). Ψ (15 mm, non-ovig., damaged), 05°14’S, 133°00’E, 25 October 1991, stn. CC21, 688– 694 m, Baruna Jaya 1 ( MNHN Is.5986).

Description. Body 2.2 times as long as greatest width, dorsal surfaces smooth, widest at pereonite 6, lateral margins weakly ovate. Rostral point present, weakly developed. Eyes separated by about 54% width of head, each eye made up of ~8 transverse rows of ommatidia, each row with ~13 ocelli, eye colour black. Pereon with transverse impressed line on pereonites 2–7; pereonite 1 and coxae 2–3 each with posteroventral angle acute, posteriorly produced; coxae 5–7 with entire oblique carina; posterior margins of pereonites 5–7 smooth. Pleon with pleonite 1 largely concealed by pereonite 7; 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, narrowly rounded; not extending beyond posterior margin of pleonite 5, posterolateral margin of pleonite 4 rounded; pleonite 5 with posterolateral angles free, not overlapped by lateral margins of pleonite 4. Pleotelson 0.7 as long as anterior width, dorsal surface without longitudinal carinae; lateral margins convex, posterior margins weakly crenulate, posterior margin converging to caudomedial point, without median point, with 0 RS.

Antennule peduncle articles 1 and 2 distinct, articulated; article 2 1.0 times as long as article 1, posterodistal angle produced to an acute point (posterior margin blade-like); articles 3 and 4 1.6 times as long as combined lengths of articles 1 and 2; article 3 3.0 times as long as wide, posterodistal angle produced to an acute point; flagellum with 26 articles, extending to posterior of pereonite 1. Antenna peduncle article 4 1.9 times as long as wide, 2.0 times as long as article 3, inferior margin with 0 plumose setae, and 0 short simple setae; article 5 1.3 times as long as article 4, 2.4 times as long as wide, inferior margin with 0 pappose setae, anterodistal angle with cluster of 10 short simple setae; flagellum with 32 articles, extending to pereonite 5.

Frontal lamina pentagonal, longer than greatest width, lateral margins concave, anterior margins concave, anterior margin narrowly rounded. Mandible incisor uni-cuspid; molar process with abundant setae; palp article 2 with ~40 distolateral setae, article 3 with ~30 RS. Maxillule with 5 terminal RS (and 6 small sub-terminal RS). Maxilla distomesial margin with 6 serrated scales. Maxilliped palp article 2 mesial margin with 0 slender setae, lateral margin distally with 0 slender setae, article 3 mesial margin with 6 slender setae, lateral margin with 7 slender setae, article 4 mesial margin with 18 slender setae, lateral margin with 10 slender setae, article 5 distomesial margin with 8 setae, lateral margin with 7 setae; endite extending beyond distal margin of palp article 3, with 3 long circumplumose setae.

Pereopod 1 basis 2.8 times as long as greatest width, superior distal angle with cluster of 0 acute setae; ischium 0.4 as long as basis, inferior margin with 5 setae (very small), superior distal margin with 0 RS (1 slender seta); merus inferior margin with 3 RS, set as single row, superior distal angle with 2 setae; carpus inferior margin with 0 RS; propodus 1.7 times as long as wide, inferior margin with 3 RS (very minute, scarcely visible acute); dactylus 1.0 as long as propodus, inferior margin strongly concave. Pereopod 2 ischium inferior margin with 2 stout RS (widely separate, 1 ventral, 1 mesial), superior distal margin with 1 RS (and 1 slender seta); merus inferior margin with 6 stout RS, set as two groups, superior distal margin with 2 acute RS; carpus inferodistal angle with 2 RS (1 large, 1 minute; and single seta). Pereopod 3 similar to pereopod 2. Pereopod 6 similar to pereopod 7. Pereopod 7 basis 2.6 times as long as greatest width, superior margin weakly convex, inferior margin with 0 palmate setae; ischium 0.5 as long as basis, inferior margin with 3 RS (set as 1 and 2), superior distal angle with 5 RS, inferior distal angle with 9 RS; merus 0.9 as long as ischium, 1.3 times as long as wide, inferior margin with 6 RS (set as 1, 2 and 3), superior distal angle with 8 RS, inferior distal angle with 7 RS; carpus 0.7 as long as ischium, 1.2 times as long as wide, inferior margin with 3 RS (set singly), superior distal angle with ~25 RS, inferior distal angle with 5 RS; propodus 1.0 times as long as ischium, 3.4 times as long as wide, inferior margin with 4 RS (set singly), superior distal angle with 0 slen- der setae (1 RS), inferior distal angle with 2 RS.

Penes flat articulating lobes, penial openings separated by 13% of sternal width, penial process 1.4 times as long as basal width (apex broadly rounded).

Pleopod 1 exopod 1.6 times as long as wide, lateral margin straight, distally broadly rounded, mesial margin strongly convex, with PMS from distal one-third; endopod 1.9 times as long as wide, distally broadly rounded, lateral margin weakly concave, with PMS from on distal margin only, mesial margin with PMS from distal one-third; peduncle 2.7 times as wide as long; mesial margin with 6 coupling hooks. Pleopod 2 appendix masculina with parallel margins, 1.0 times as long as endopod, distally acute (with small apical lobe). Pleopods 2–5 peduncle distolateral margin without prominent acute RS; pleopods 3–5 endopods without distomesial serrate scales.

Uropod peduncle ventrolateral margin with 2 RS, lateral margin with medial short acute RS, posterior lobe about one-third as long as endopod; rami extending to pleotelson apex, marginal setae in single tier, apices broadly rounded. Endopod apically not bifid; lateral margin straight, proximal lateral margin with 0 RS; distal lateral margin with 0 RS, mesial margin strongly convex, with 9 RS. Exopod not extending to end of endopod, 3.8 times as long as greatest width, apically not bifid; lateral margin weakly convex, with 11 RS; mesial margin weakly convex or weakly concave, with 4 RS.

Female: Similar to male but for the sexual characters.

Variation: Robust setae: pleotelson (n =11) always without RS. Uropod setation far from uniform, and pattern is only loosely as stated in the description. Uropod exopod mesial margin (n =22) with 3–5 RS, 3 (36%), 4 (55%) or 5 (9%), lateral margin (n =20) with 7–13 RS, 11 (45%) or 12 (20%) most frequent; uropod endopod mesial margin (n=22) with 7–12 RS, 7 (18%), 8 (50%) or 9 (14%) most frequent, 0 and 12 each occurring once, lateral margin (n=20) with only 0+3 (45%) or 0+2 (40%), 1+3 occurring twice, 0+4 once. There is no discernable difference between males and females; the number of RS are frequently different on the left and right rami, as well as between individuals; in smaller or juvenile individuals the apex of the pleotelson is more evident ( Fig. 1 G) than in the larger (> 30 mm) specimens ( Fig. 1 F).

Pereopods 2 and 3: Males of several species of Tridentella have a large, conical robust seta at the inferodistal angle of pereopods 2 and 3. Development and maturity changes have not been recorded in the genus, but this difference is not solely due to size. The two large specimens recorded here are of similar size, and both have equally developed penial processes and appendix masculina, but only one has the large carpal robust setae, and furthermore has more robust setae on the inferior margins of pereopods 1–3 ( Figs 3 A and C, 3B and D).

Size: Adult males 32 and 33 mm; non-ovigerous females 15–40 mm (mean = 21 mm); mancas 14.0– 15.5 mm.

Remarks: The large size, broadly rounded pleotelson posterior margin, complete lack of dorsal ornamentation and antennule peduncle articles 2 and 3 each with the posterodistal angle being produced, distinguishes Tridentella memikat sp. nov. from all other species in the family.

Distribution: Banda Sea Indonesia, at depths from 620 to 809 metres.

Etymology: The epithet is an Indonesian word meaning engross or fascinating (noun in apposition).

Figures

FIGURE 1. Tridentella memikat sp. nov. A – D, F, I, holotype; J, K, ♂ 33 mm and E, G and H, & 27 mm, paratypes. A, dorsal view; B, lateral view; C, head; D, frons; E, pleonites, lateral view; F, pleotelson, holotype; G, pleotelson, & paratype; H, pleotelson posterior margin, apex; I, penial processes, in situ; J, antennule; K, antenna peduncle.

FIGURE 2. Tridentella memikat sp. nov. Paratype ♂ 33 mm. A, mandible; B, mandibular molar process; C, maxillule; D, maxillule apex; E, maxilla; F, maxilla apex; G, maxilliped; H, maxilliped endite, apex; I, maxilliped palp articles 4 and 5.

FIGURE 3. Tridentella memikat sp. nov. A, B, G, holotype, remainder paratype ♂ 33 mm. A, pereopod 1; B, pereopod 2; C, pereopod 1; D, pereopod 2; E, pereopod 3; F, pereopod 1 dactylus; G, pereopod 7.

FIGURE 4. Tridentella memikat sp. nov. Paratype ♂ except F, paratype & 27 mm. A – D, pleopods 1 – 3, 5; E, uropod exopod, ventral view; F, G, uropods dorsal view.