Tridentella magna, 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 : 112-116

Tridentella magna sp. nov. Figs 10–13

Holotype: ♂ (36 mm), New Caledonia, Ride des Loyauté , Mont K, 24°43.49’S, 170°07.70’E, 24 November 1993, BATHUS 3, stn, DW778, 750 – 760 m, N.O.“ Alis ”, Bouchet, Richer de Forges-IRD & Warén coll. (MNHN-IU- 2017-21).

Description: Body 2.1 times as long as greatest width, dorsal surfaces smooth, widest at pereonites 5 and 6, lateral margins ovate. Head anterior margin with raised ridge and posteriorly with 3 low submarginal tubercles, rostral point absent. Eyes separated by about 0.6% width of head, each eye made up of ~9 transverse rows of ommatidia, each row with ~14 ommatidia, eye colour black. Pereon with transverse impressed line absent on all pereonites; pereonite 1 and coxae 2–3 each with posteroventral angle acute, posteriorly produced and with small distinct produced point; coxae 5–7 with entire oblique carina; posterior margins of pereonites 5–7 smooth. Pleon with pleonite 1 largely concealed by pereonite 7; pleonites 3–5 posterior margin smooth; posterolateral angles of pleonite 2 rounded, not posteriorly produced; pleonite 3 with posterolateral margins not extending to posterior margin of pleonite 4, rounded; posterolateral margins of pleonite 4 not extending beyond posterior margin of pleonite 5, rounded; pleonite 5 with posterolateral angles free, not overlapped by lateral margins of pleonite 4. Pleotelson 0.8 times as long as anterior width, dorsal surface without longitudinal carinae; surface smooth; lateral margins convex, smooth; posterior margin weakly crenulate (very weak indentations distally), posterior margin converging to caudomedial point, with small distinct 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 produced to an acute point; articles 3 and 4 1.2 times as long as combined lengths of articles 1 and 2; article 3 2.7 times as long as wide, posterodistal angle not produced (with 'exopod', Fig. 11C ); flagellum with 22 articles, extending to middle of pereonite 1. Antenna peduncle article 4 1.3 times as long as wide, 1.4 times as long as article 3, inferior margin with 0 plumose setae, and 4 short simple setae; article 5 1.3 times as long as article 4, 2.6 times as long as wide, inferior margin with 1 pappose setae, anterodistal angle with cluster of 7 short simple setae; extending to middle of pereonite 5.

Frontal lamina pentagonal, longer than greatest width, lateral margins diverging strongly and abruptly towards anterior, anterior margins concave. Maxilliped palp article 2 mesial margin with 2 slender setae, lateral margin distally with 0 slender setae, article 3 mesial margin with 8 slender setae, lateral margin with 8 slender setae, article 4 mesial margin with 14 slender setae, lateral margin with 14 slender setae, article 5 distomesial margin with 10 setae, lateral margin with 4 setae; endite extending beyond distal margin of palp article 3, with 1 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 0 setae, superior distal margin with 0 RS and 1 simple seta; merus inferior margin with 5 RS (two tiny, 3 large), set as single row, superior distal angle with 2 setae; carpus inferior margin with 0 RS; propodus 1.9 times as long as wide, inferior margin with 1 RS at base of dactylus; propodal palm straight; dactylus 0.7 times as long as propodus. Pereopod 2 more slender than pereopod 1. Pereopod 2 ischium inferior margin with 1 stout acute RS, superior distal margin with 1 RS; merus inferior margin with 6 stout RS, set as two groups, superior distal margin with 3 acute RS (short, acute); carpus inferodistal angle with 1 RS (massive, 0.6 times as long as carpus). Pereopod 2 propodal palm with 3 RS (2 minute RS on palm, 3rd opposing dactylus). Pereopod 3 similar to pereopod 2. Pereopod 4 intermediate in form between pereopods 3 and 5. Pereopod 6 similar to pereopod 7. Pereopod 7 basis 2.9 times as long as greatest width, superior margin weakly convex, inferior margin with 0 palmate setae; ischium 0.4 times as long as basis, inferior margin with 2 RS (small), superior distal angle with 5 RS, inferior distal angle with 5 RS; merus 0.9 times as long as ischium, inferior margin with 6 RS (set as three pairs), superior distal angle with 12 RS, inferior distal angle with 10 RS; carpus 0.9 times as long as ischium, 0.7 times as long as wide, inferior margin with 6 RS (set as 3 pairs), superior distal angle with 11 RS, inferior distal angle with 11 RS; propodus 1.2 times as long as ischium, 3.1 times as long as wide, inferior margin with 9 RS (set as 3 pairs), superior distal angle with 3 slender setae, inferior distal angle with 3 RS.

Penes flat articulating, distally rounded lobes, penial openings separated by 12% of sternal width, penial process 1.5 times as long as basal width.

Pleopod 1 exopod 1.6 times as long as wide, lateral margin straight, distally broadly rounded, mesial margin weakly convex, with PMS from distal one-third, with ~74 PMS; endopod 1.9 times as long as wide, distally broadly rounded, lateral margin weakly concave, with PMS on distal margin only, mesial margin with PMS from distal half, endopod with ~37 PMS; peduncle 2.4 times as wide as long; mesial margin with 9 coupling hooks. Pleopod 2 exopod with ~90 PMS, endopod with ~45 PMS; appendix masculina with parallel margins, 1.2 times as long as endopod, distally bluntly rounded. Pleopod 3 exopod with ~105 PMS, endopod with ~45 PMS.

Uropod peduncle ventrolateral margin with 2 small acute RS, lateral margin without medial short acute robust seta, posterior lobe about less than one-third as long as endopod; rami extending to pleotelson apex, apices acute. Endopod apically not bifid; lateral margin weakly convex, proximal lateral margin with 1 RS; distal lateral margin with 3 RS, mesial margin straight, with 7 RS. Exopod not extending to end of endopod, 3.9 times as long as greatest width, apically not bifid; lateral margin weakly convex, with 11 RS; mesial margin sinuate, proximally concave, with 3 RS.

Female: Not known.

Remarks: Tridentella magna sp. nov. is characterized by its large size (largest species in the family at 36 mm compared to a size range of 6.9–18.0 mm for all other species, with only the four large species described or mentioned herein exceeding 25 mm in total body length), unornamented pleon and pleotelson, the head anterior margin with a distinct sub-marginal and three low sub-marginal nodules posteriorly, and antennula peduncle article 2 with the posterodistal angle produced and acute.

Tridentella memikat Bruce, 2008 (Banda Sea, Indonesia) is the only similar species, sharing the large adult size (32, 33 mm), lack of ornamentation, and antennula morphology, together with closely similar frontal lamina, pereopods and pleopods. Tridentella magna differs from T. memikat most obviously in the cephalic ornamentation and the shape of the uropodal endopod, which in T. magna has a very short mesial margin and wide nearly straight posterior margin; in contrast T. memikat has a long mesial margin with a clear point of inflection to the posterior margin.

There are two other large species in the family, Tridentella recava Bowman, 1986 (northwestern Atlantic; up to 26 mm) and Tridentella tanimbar Bruce, 1986 (Banda Sea, Indonesia; 31 mm). Both these smooth-bodied species have the pleotelson apex deeply incised and a short and wide clypeus and are not likely to be confused with Tridentella magna sp. nov.

Etymology: From the Latin magnus, alluding to the large size in relation to other species of the family.

Figures

FIGURE 10. Tridentella magna sp. nov., holotype male (36 mm, MNHN-IU-2017-21). A, habitus, dorsal view; B, habitus, lateral view; C, head, dorsal view; D, frons; E, pleonites; F, pleotelson; G, distal margin of pleotelson; H, penial processes.

FIGURE 11. Tridentella magna sp. nov., holotype male (36 mm, MNHN-IU-2017-21). A–C, antennula, viewed from various angles; D, flagellum of antennula; E, antenna; F, maxilliped; G, distal seta of basis.

FIGURE 12. Tridentella magna sp. nov., holotype male (36 mm, MNHN-IU-2017-21). A, pereopod 1; B, carpus–dactylus of pereopod 1;C, pereopod 2; D, pereopod 7.

FIGURE 13. Tridentella magna sp. nov., holotype male (36 mm, MNHN-IU-2017-21). A, pleopod 1; B, pleopod 2; C, pleopod 3; D, uropod, in situ; E, right exopod, in situ.