Aega rickbruscai, 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 : 196-202

AEGA RICKBRUSCAI SP. NOV. ( FIGS 40–44 , 63 )

Material examined

Type material all from New Caledonia.

Holotype: ♂ (44 mm), 18∞50.0¢S, 163∞14.5¢E, 20.ix.1985, stn 0199, MUSORSTOM IV, 595 m ( MNHN Is.5806).

Paratypes: ♂ (50 mm, part dissected), 18∞53.80¢S, 163∞14.10¢E, 20.ix.1985, stn 0200, MUSORSTOM IV, 535 m ( MNHN Is.5805) . ♂ (29 mm), 19∞45.30¢S, 158∞46.30¢E, 19.x.1986, stn 0364, MUSORSTOM V, 675 m ( MNHN Is.5808) . ♀ (ovig. 59 mm, damaged), 19∞37.70¢S, 158∞43.90¢E, 21.x.1986, stn 0380, MUSORSTOM V, 555–570 m ( MNHN Is.5807) . 2 ♂ (24, 25 mm), 2 ♀ (non-ovig. 43, 47 mm), 19∞40.85¢S, 158∞46.10¢E, 21.x.1986, stn 0383, MUSORSTOM V, 615– 600 m ( MNHN Is.5804) .

Non-type: ♂ (44 mm), Cavalli Sea Mount , off northern North Island, New Zealand , 34∞07.21¢S,

174∞05.64¢E, 16.iv.2002, 554– 549 m, coll. Steve O’Shea on R.V. Kaharoa (KAH 0204/27; NIWA 3444).

Description

Body 2.0 times as long as greatest width, dorsal surfaces smooth (finely punctate), widest at pereonite 5, lateral margins ovate. Rostral point projecting anteriorly, not ventrally folded. Eyes large, medially united, anterior clear field 11% length of head, posterior clear field 34% length of head; each eye made up of ~25 transverse rows of ommatidia, each row with ~12–14 ommatidia; eye colour dark brown. Pereonite 1 and coxae 2–3 each with posteroventral angle with small distinct produced point; 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 0.9 times as long as anterior width, dorsal surface without longitudinal carina; lateral margins convex, smooth, posterior margin with elongate medial point, with 0 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, article 3 3.1¥ LW; flagellum with 11 articles, extending to mid-point of eye. Antenna peduncle article 2 inferior surface with distinct longitudinal suture; article 4 2¥ LW, 1.4 times as long as combined lengths of articles 1–3, without deep longitudinal groove (with longitudinal depression), inferior margin with 1 plumose seta, and 0 short simple setae; article 5 not markedly wider or flatter than article 4, 0.9¥ L article 4, 2.3¥ LW, inferior margin with 2 plumose setae, anterodistal angle with cluster of 5 short simple setae; flagellum with 22 articles, extending to posterior of pereonite 1.

Frontal lamina flat, longer than greatest width, oval (rounded-ovate in shape), anterior margin rounded, with small median point, posterior margin not abutting clypeus.

Mandible molar process absent; palp article 2 with 8 distolateral setae (3 long), palp article 3 with 36 setae. Maxillule with 9 terminal RS. Maxilla medial lobe with 4 RS (2 hooked, 2 straight); lateral lobe with 3 RS. Maxilliped endite with 2 apical setae; palp article 2 with 3 RS (small hooked); article 3 with 4 recurved RS (plus 1 straight); article 4 with 6 hooked RS (4 large, 2 small); article 5 partly fused to article 4, with 6 RS (3 hooked, 3 straight).

Pereopod 1 basis 2 times as long as greatest width; ischium 0.5¥ L basis, inferior margin with 0 RS, superior distal margin with 3 RS (long acute); merus inferior margin with 8 RS, set as 2 groups (of 6 and 2), superior distal angle with 6 RS (long acute); carpus 0.5¥ L merus, inferior margin with 0 RS (with distal flange); propodus 1.3 times as long as proximal width, inferior margin with 0 RS, propodal palm with large distal lobe, dactylus smoothly curved, 1.6¥ L propodus. P2 ischium inferior margin with 1 RS (inferior distal angle with 4 slender acute RS), superior distal margin with 4 RS; merus inferior margin with 12 RS, set as single row, superior distal margin with 1 acute RS; carpus similar in size to that of P1, inferodistal angle with 0 RS, propodus without large club-shaped distal RS. P3 similar to P2 (longer, with more acute RS on inferior margin of ischium); propodus without large club-shaped distal RS. P6 similar to P7. P7 basis 3.2 times as long as greatest width, inferior margin with 14 palmate setae (medial and lateral margins with 5 and 9, respectively); ischium 0.6¥ L basis, inferior margin with 12 RS (set as row of 7 long and 5 short marginal RS), superior distal angle with 7 RS, inferior distal angle with 9 RS (2 long and 8 short); merus 0.8 L ischium, 1.7¥ LW, inferior margin with 8 RS (3 long acute and 1 short RS and 4 short submarginal RS), superior distal angle with 8 RS, inferior distal angle with 7 RS (3 short, 4 slender and long); carpus 0.9¥ L ischium, 2.8¥ LW, inferior margin with 5 RS (set as 3 long and 2 short), superior distal angle with 9 RS, inferior distal angle with 10 RS; propodus 0.8¥ L ischium, 4.3¥ LW, inferior margin with 5 RS (3 long and 2 short), superior distal angle with 7 slender setae (simple and palmate, including 1 RS), inferior distal angle with 4 RS.

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

Pleopod 1 exopod 1.8¥ LW, distally narrowly rounded with strongly oblique medial margin, lateral margin distally concave, medial margin strongly convex, with PMS from base; endopod 1.8¥ LW, distally subtruncate, lateral margin strongly concave (widest distally, proximally concave), with PMS from on distal margin only, medial margin with PMS from distal half; peduncle 1.8¥ WL, medial margin with 14 coupling hooks. Pleopod 2 appendix masculina with straight margins, 0.6¥ 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 0.75¥ 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 or broadly rounded (endopod narrow, exopod broad). Endopod apically not bifid, lateral margin proximally convex, with prominent excision positioned about threequarters along ramus, proximal lateral margin with 2 RS, distal lateral margin with 5 RS, medial margin weakly convex (appearing straight), with 5 RS. Exopod extending beyond end of endopod, 2.5 times as long as greatest width, apically not bifid; lateral margin weakly convex, with 11 RS; medial margin convex, with 6 RS.

Female

Males and non-ovigerous females appear entirely similar with the exception of the sexual characters. The single ovigerous female differs in having the eyes very narrowly separated, the dorsal surface of the head notably depressed, and the RS on the merus of P1 notably elongate and acute. Five pairs of oostegites are present, on sternites 1–5.

Size

Males measured 24–50 mm (mean = 34 mm), nonovigerous females 43 and 47 mm, and the single ovigerous female 59 mm.

Variation

Robust setae: pleotelson without RS. Uropod exopod medial margin (n = 16) 4 (12%), 5 (44%), 6 (44%), lateral margin 9 (25%), 10 (44%), 11 (31%); uropod endopod (n = 16) medial margin 5 (56%), 6 (37.5%) or 7 once, lateral margin with 2 + 5 (25%), 2 + 5 (56%), 2 + 6, 1 + 5 and 3 + 5, all once. There is no discernible difference between males and females, nor does the number of RS increase with the size of the specimen, some of the smaller specimens having more RS than the larger.

P1–3 had slightly variable counts for the RS on the inferior margin of the merus: P1 had 6 + 2 (81%), P2 had 12–14 with 12 (69%) and 13 (25%) most frequent, P3 had 13–15 with 13 (37.5%) and 14 (50%) and 15 (12.5%).

All material from New Caledonia is pale cream in colour. The recently collected specimen from New Zealand is pale orange-brown, with sparse brown chromatophores; the colour is darkest on the lateral margins of the pleon. The eyes of this specimen are a dark red–brown.

Remarks

Aega rickbruscai sp. nov. is readily identified by the huge eyes with very little anterior free space, the ovate and anteriorly acute frontal lamina, pereopod 1 merus inferior margin usually with 8 robust setae (set as 6 + 2), pereopods 2 and 3 merus inferior margin with a single row of 12–14 and 13–15 robust setae, respectively, pereopods 5–7 with long robust setae on the inferior margin and the wide uropodal exopod very obviously extend beyond the endopod apex.

Aega rickbruscai is distinguished from the very similar and fully sympatric (both species were taken together at one station) A. musorstom sp. nov. by the lack of a propodal blade on pereopods 1–3 as well as the propodus of pereopods 2 and 3 being more slender than that of pereopod 1. In addition, A. rickbruscai is larger, the anterior margin of the frontal lamina forms an indistinct point, the uropodal exopod is wider and the number of robust setae on the uropodal rami, while overlapping, is fewer. Aega rickbruscai has a narrower range of variation in the number of robust setae on pereopods 1–3. Character states that are shared by these two species include the pleotelson lacking robust setae, the ischium of pereopods 2 and 3 being provided with long acute setae, a similar pattern of setation on pereopods 1–3, long acute robust setae on pereopods 4–7, and similar uropod shape and setation.

Aega rickbruscai is also similar to A. hamiota sp. nov., both having very large eyes, long acute robust setae on pereopods 4–7 and wide uropodal rami, but is readily distinguished by lacking long acute robust setae on the superior margins of the ischium, merus and carpus of pereopods 4–7, a less wide uropodal exopod and by the lack of robust setae on the pleotelson.

Prey

Not known.

Distribution

Known only from New Caledonia and northern New Zealand; at depths between 535 and 615 m.

Etymology

Named for Richard C. Brusca, in recognition of his contributions to knowledge of the Isopoda , and in acknowledgement of his monographs on the East Pacific Aegidae ( Brusca, 1983; Brusca & France, 1992).

Figures

Figure 40. Aega rickbruscai sp. nov. A–E, holotype, remainder ♂ paratype 50 mm. A, dorsal view. B, lateral view. C, head, dorsal view. D, frons. E, antenna peduncle. F, antenna peduncle, articles 1–3, ventral view. G, antennule. H, sternite 7 showing penial openings.

Figure 41. Aega rickbruscai sp. nov. Male paratype. A, mandible. B, mandible palp article 3. C, maxillule. D, maxillule apex. E, maxilla. F, maxilla, apex detail. G, maxilliped. H, maxilliped palp articles 2–4. I, maxilliped palp article 5, dorsal view.

Figure 42. Aega rickbruscai sp. nov. A, E, holotype, remainder ♂ paratype 50 mm. A–E, pereopods 1–3, 6 and 7, respectively. F, pereopod 2, mesial surface, distal angle of ischium.

Figure 43. Aega rickbruscai sp. nov. A, B, holotype. C–E, male paratype. F, G, ovigerous female paratype. A–E, pleopods 1–5, respectively. F, dorsal view of head. G, pereopod 1, distal articles.

Figure 44. Aega rickbruscai sp. nov. Male paratype. A, uropod. B, uropod exopod, ventral view. C, uropod endopod apex. D, uropod exopod apex.

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).