Aega banda, Bruce, 2004

Bruce, Niel L., 2004, Reassessment of the isopod crustacean Aega deshaysiana (Milne Edwards, 1840) (Cymothoida: Aegidae): a worldwide complex of 21 species, Zoological Journal of the Linnean Society 142 (2), pp. 135-232 : 162-166

AEGA BANDA SP. NOV. ( FIGS 16 , 17 , 63 )

Material examined

Holotype: ♂ (30 mm), Kei Islands , eastern Banda Sea, Indonesia, 5∞29¢S, 132∞37¢E, 12.v.1922, stn 58, trawl, 290 m, mud, coll. Th. Mortensen, ‘ Danske Exped. til Kei-Øerne 1922’ ( ZMUC CRU3736 ).

Non-type: ♀ (non-ovig. 50 mm), North West Shelf , Western Australia, 17∞59.4¢S, 118∞18.4¢E, 28.i.1984, 406– 416 m, Sta. T 7, coll. A.J. Bruce on FRV Soela ( NTM Cr000590) .

Description

Body 2.5 times as long as greatest width, dorsal surfaces smooth, widest at pereonite 5, lateral margins weakly ovate. Rostral point projecting anteriorly, not ventrally folded. Eyes large, not medially united, separated by about 2% width of head; each eye made up of ~20 transverse rows of ommatidia, each row with ~10 ommatidia; eye colour faded, not known. Pereonite 1 and coxae 2–3 each with posteroventral angle rounded; coxae 5–7 with entire oblique carina. Pleon with pleonite 1 visible in dorsal view; pleonite 4 with posterolateral margins extending clearly beyond posterior margin of pleonite 5; pleonite 5 with posterolateral angles overlapped by lateral margins of pleonite 4. Pleotelson 1.1 times as long as anterior width, dorsal surface without longitudinal carina; lateral margins weakly convex (distally weakly sinuate), smooth, posterior margin with elongate medial point, with 12 RS.

Antennule peduncle articles 1 and 2 flattened, article 2 without anterodistal lobe; articles 3 and 4 0.7 times as long as combined lengths of articles 1 and 2; flagellum with 10 articles, extending to anterior of pereonite 1. Antenna peduncle article 2 inferior surface with indistinct groove; article 4 2.1¥ LW, 1.2 times as long as combined lengths of articles 1–3; article 5 not markedly wider or flatter than article 4, 0.9¥ L article 4, 2.7¥ LW; flagellum with 19 articles, extending to middle of pereonite 3.

Frontal lamina flat, longer than greatest width, lateral margins converging posteriorly, posteriorly rounded, anterior margin rounded, with small median point, posterior margin not abutting clypeus.

Maxilliped endite with 1 apical seta; palp article 2 with 3 RS (straight); article 3 with 5 recurved RS (and 1 straight); article 4 with 6 hooked RS; article 5 partly fused to article 4, with 4 RS (1 hooked, 3 straight).

Pereopod 1 basis 2.2 times as long as greatest width; ischium 0.5¥ L basis, inferior margin with 0 RS, superior distal margin with 2 RS; merus inferior margin with 4 RS, set as 2 groups (of 2 and 2), superior distal angle with 2 RS; carpus 0.6¥ L merus, inferior margin with 0 RS; propodus 1.4 times as long as proximal width, inferior margin with 0 RS, propodal palm with small distal lobe, dactylus smoothly curved, 1.4 L propodus. P2 ischium inferior margin with 2 RS, superior distal margin with 2 RS; merus inferior margin with 8 RS, set as single row, superior distal margin with 2 acute RS; carpus longer than that of P1, with inferodistal lobe, inferodistal angle with 1 RS (minute), propodus without large club-shaped distal RS. P3 similar to P2; propodus without large club-shaped distal RS. P6 similar to P7. P7 basis 3 times as long as greatest width, inferior margin with 16 palmate setae; ischium 0.6¥ L basis, inferior margin with 7 RS (set as 1, 1, 3, 1 and 1), superior distal angle with 6 RS, inferior distal angle with 5 RS; merus 0.9¥ L ischium, 2.1¥ LW, inferior margin with 8 RS (set as 1, 3, 1, 2 and 1), superior distal angle with 10 RS, inferior distal angle with 7 RS; carpus 1.1¥ L ischium, 3.7¥ LW, inferior margin with 4 RS (set as 2 and 2), superior distal angle with 6 RS, inferior distal angle with 7 RS; propodus 0.8¥ L ischium, 5.9¥ LW, inferior margin with 3 RS (set as 1 and 2), superior distal angle with 3 slender setae (plus 1 RS), inferior distal angle with 4 RS.

Penes opening flush with surface of sternite 7; penial openings separated by 6% of sternal width.

Pleopod 1 exopod 2.3 ¥ LW, distally narrowly rounded with strongly oblique medial margin, lateral margin distally concave, medial margin strongly convex, with PMS from base; endopod 2.2¥ LW, distally subtruncate, lateral margin sinuate (widest subdistally, proximally concave), with PMS from on distal margin only, medial margin with PMS from distal half; peduncle 1.6¥ WL, medial margin with 10 coupling hooks. Pleopod 2 appendix masculina with straight margins, 0.7¥ L endopod, distally narrowly rounded. Exopods of pleopods 1–5 each, with distolateral margin not deeply serrate; endopods of pleopods 3–5 each with mediodistal point; pleopods 2–5 peduncle distolateral margin without prominent acute RS.

Uropod peduncle ventrolateral margin with 2 RS, posterior lobe about two-thirds L endopod. Uropod rami not coplanar, exopod at angle of about 135 ∞ to endopod, rami not extending beyond pleotelson, marginal setae in single tier, apices narrowly rounded. Endopod apically not bifid, lateral margin proximally convex or distally straight, with prominent excision positioned about two-thirds along ramus, proximal lateral margin with 5 RS, distal lateral margin with 6 RS, medial margin weakly convex, with 5 RS. Exopod extending beyond end of endopod, 3.4 times as long as greatest width, apically not bifid; lateral margin straight, with 9 RS; medial margin sinuate, proximally concave, with 5 RS.

Female

Similar to male, perhaps growing to a substantially larger size.

Variation

Robust setae: range of the 2 specimens only. Pleotelson indicating a range from 5 + 5 to 6 + 6, possibly an additional terminal pair as both apices were crushed. Uropod exopod medial margin with 4 or 5 (once), lateral margin 8 or 9; uropod endopod medial margin varies from 4 to 7, lateral margin with 5 + 5 (both rami, Western Australian specimen), 6 + 5 and 7 + 5.

P1 setation of the merus with 2 + 2 (all); P2 merus 7 or 8 (once); P3 merus with 7 or 8.

Size

Male 30 mm, female 50 mm.

Remarks

The characters by which A. banda sp. nov. is most readily identified are the very narrowly separated eyes, relatively long antennule and antenna, slender uropodal rami, presence of ‘long’ robust setae on the posterior pereopods and the pattern of setation of the inferior margin of the merus of pereopods 1–3.

Aega banda is a species that, with casual examination, appears similar to many other species in the group. However, all other species are readily excluded by clear-cut differences in several characters. The narrow uropodal exopod eliminates A. hamiota sp. nov., A. musorstom sp. nov., A. rickbruscai sp. nov. and A. trulla sp. nov.; lack of a propodal blade on pereopods 1–3 eliminates A. birubi sp. nov., A. kixalles sp. nov., A. trulla and again A. musorstom ; the uropodal exopod extending distinctly beyond the endopod apex eliminates A. deshaysiana , A. kwazulu sp. nov., A. excisa , A. japonica sp. nov. and A. umpara sp. nov.; and finally the presence of long acute robust setae on the posterior pereopods eliminates the remaining species, A. antillensis A. alazon sp. nov. and A. warna sp. nov.

The specimen from tropical Western Australia, the only specimen of this group of species recorded from the eastern Indian Ocean, while much larger than the holotype, agrees well with most characters. It is excluded from the type series as the location is a considerable distance from the type locality and there are some minor differences, notably that the antennal flagellum is slightly shorter (not extending to pereonite 3, possibly a sex-related difference) and the pleotelson robust setae are more widely spaced. The arrangement of the robust setae of pereopods 1–3 is consistent with that expected within a species, and the arrangement and size of the robust setae of the posterior pereopods correspond strongly between the two specimens. The shape and proportions of the uropodal rami similarly correspond well with that of the holotype and the variation in numbers of robust setae on the uropodal margins falls within that shown by species for which there are good data (e.g. A. antillensis , A. deshaysiana , A. alazon sp. nov. and A. musorstom sp. nov.).

The description given here is abbreviated, taken only from the holotype, and dissection was minimized to avoid excessive mutilation of the specimen. The antennule, antenna, mouthparts other than the maxilliped, pleopods 3–5 and the uropods were not dissected off and where practical, examined and drawn in situ.

Prey

Not known.

Distribution

Eastern Indian Ocean off the north-west shelf of Western Australia to the Kei Islands, eastern Banda Sea, Indonesia; at depths ranging between 290 and 416 m.

Etymology

The epithet is taken from the Banda Sea. The Kei (or Kai) Islands are at the eastern end of this sea, part of the Moluku Archipelago and subregion of Indonesia); noun in apposition.

Figures

Figure 16. Aega banda sp. nov. Holotype, ZMUC CRU3736. A, dorsal view. B, lateral view. C, frons. D, head, dorsal view. E, sternite 7 showing penial openings. F, maxilliped palp. G, maxilliped palp, article 5.

Figure 17. Aega banda sp. nov. Holotype, ZMUC CRU3736. A, pereopod 1. B, pereopod 2. C, mediodistal angle of ischium. D, pereopod 7. E, pleopod 1. F, pleopod 2. G, uropod (in situ). H, uropod endopod, ventral view (in situ).

Figure 63. Distributions of: Aega banda sp. nov. (*), A. birubi sp. nov. (•), A. hamiota sp. nov. (-), A. kixalles sp. nov. (O) and A. rickbruscai sp. nov. (Ŧ).