Aega musorstom, 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 : 190-196

AEGA MUSORSTOM SP. NOV. ( FIGS 35–39 , 64 )

Material examined

Holotype: ♂ (33 mm), off New Caledonia, 18∞57.0¢S, 163∞12.6¢E, 19.ix.1985, Stn 0170, 480 m, coll. MUSORSTOM IV ( MNHN Is.8503).

Paratypes: All material from New Caledonia . 2 ♂ (35 [dissected], 39 mm), 2 ♀ (non-ovig. 32, 31 mm), same data as holotype ( MNHN Is. 5792) . 3 ♂ (29, 35, 37 mm), MUSORSTOM IV, 18∞55.8¢S, 163∞13.87¢E, 20.ix.1985, Stn 0201, ‘ Synagonopi sp. 1’, 490 m, coll. MUSORSTOM IV ( MNHN Is. 5796) . 4 ♂ (26, 27, 31, 35 mm), 18∞56.6¢S, 163∞13.7¢E, 18.ix.1985, Stn 0179, 475 m, coll. MUSORSTOM IV ( MNHN Is. 5802) . ♂ (22 mm), 18∞58.0¢S, 163∞59.3¢E, 20.ix.1985, Stn 0202, 560 m, coll. MUSORSTOM IV ( MNHN Is. 5797) . ♂ (29 mm), 19∞40.85¢S, 158∞46.10¢E, 21.x.1986, stn 0383, MUSORSTOM V, 615– 600 m ( MNHN Is. 5799) . ♂ (21 mm), 20∞44.95¢S, 160∞53.67¢E, 22.x.1986, Stn 0389, 500 m, coll. MUSORSTOM V ( MNHN Is. 5801) . ♀ (non-ovig. 36 mm), 19∞36.43¢S, 158∞43.41¢E, 18.x.1986, Stn 0355 580 m, coll. MUSORSTOM V ( MNHN Is. 5795) . ♂ (26 mm), 2 ♀ (non-ovig. 31, 33 mm), Loyalty Islands, 21∞05.13¢S, 167∞32.11¢E, 21.ii.1989, Stn CP 467, 575 m, coll. MUSORSTOM VI ( MNHN Is. 5793) . ♂ (29 mm), Loyalty Islands, 21∞03.56¢S, 167∞32.25¢E, 21.ii.1989, Stn CP 465, 575 m, coll. B. Richer de Forges, MUSORSTOM VI ( MNHN Is. 5800) . ♂ (25 mm) Chesterfield Islands, 20∞50.69¢S, 160∞55.25¢E, 21.vii.1988, Stn DE 15¢, 580– 590 m, coll. CORAIL 2 ( MNHN Is. 5798) . ♂ (31 mm), ♀ (non-ovig. 36 mm), Chesterfield Islands, 20∞48.14¢S, 160∞57.14¢E, 21.vii.1988, Stn Cp 17, 580– 590 m, coll. B. Richer de Forges, CORAIL 2 ( MNHN Is. 5794) .

Description

Body 2.0–2.4 times as long as greatest width, dorsal surfaces sparsely 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 35% length of head; each eye made up of ~26 transverse rows of ommatidia, each row with ~12–14 ommatidia; eye colour pale 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 1.0 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 2.9¥ LW; flagellum with 11 articles, extending to posterior margin of eye. Antenna peduncle article 2 inferior surface without distinct longitudinal suture; article 4 1.8¥ LW, 1.4 times as long as combined lengths of articles 1–3, without deep longitudinal groove, 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, 2.1¥ LW, inferior margin with 2 plumose setae, anterodistal angle with cluster of 2 short simple setae (and 1 plumose seta); flagellum with 20 articles, extending to middle of pereonite 1.

Frontal lamina flat, longer than greatest width, oval (rounded-ovate in shape), anterior margin rounded, without small median point, posterior margin not abutting clypeus.

Mandible molar process absent; palp article 2 with 8 distolateral setae, palp article 3 with 32 setae. Maxillule with 8 terminal RS (falcate). Maxilla medial lobe with 3 RS; lateral lobe with 4 RS (2 recurved, 2 straight and finely serrate). Maxilliped endite with 1 apical seta; palp article 2 with 3 RS (small hooked); article 3 with 4 recurved RS (hooked and 1 straight); article 4 with 5 hooked RS; article 5 partly fused to article 4, with 6 RS (straight, 3 stout and 3 acute).

Pereopod 1 basis 2.1 times as long as greatest width; ischium 0.6¥ L basis, inferior margin with 0 RS (2 simple setae), superior distal margin with 0 RS (2 small simple setae); merus inferior margin with 7 RS, set as single row or 2 groups (of 5 and 2), superior distal angle with 5 RS (slender simple setae); carpus 0.5¥ L merus, inferior margin with 0 RS (formed into thickened ridge); propodus 1.3 times as long as proximal width, inferior margin with 0 RS, propodal palm with distal blade (rectilinear, extending from the entire length of the propodus inferior margin), dactylus smoothly curved, 1.7¥ L propodus. P2 ischium inferior margin with 5 RS (slender acute), superior distal margin with 2 RS (slender acute); merus inferior margin with 12 RS, set as 2 rows (irregular double row), superior distal margin with 5 acute RS (long); carpus similar in size to that of P1, inferodistal angle with 0 RS, propodus without large club-shaped distal RS. P3 similar to P2 (ischium inferior margin with 8 long acute RS, merus inferior margin with 13 stout RS); propodus without large club-shaped distal RS. P6 similar to P7 (but more robust and shorter, with more and longer RS; basis 2.6¥ LW). P7 basis 3.2 times as long as greatest width, inferior margin with 22 palmate setae (medial and lateral margins with 10 and 12, respectively); ischium 0.5¥ L basis, inferior margin with 12 RS (set as row of 7 long and 5 short marginal RS), superior distal angle with 8 RS, inferior distal angle with 7 RS (2 of which are long and acute); merus 0.9¥ L ischium, 2.2¥ LW, inferior margin with 7 RS (3 long acute and 1 short RS and 3 short submarginal RS), superior distal angle with 5 RS, inferior distal angle with 14 RS; carpus 0.9¥ L ischium, 2.6¥ LW, inferior margin with 5 RS (set as a loose cluster of 2 and 3 RS), superior distal angle with 7 RS, inferior distal angle with 12 RS; propodus 0.8¥ L ischium, 2.5¥ LW, inferior margin with 4 RS (set as 1, 1 and 2), superior distal angle with 6 slender setae (simple), inferior distal angle with 4 RS.

Penes opening flush with surface of sternite 7; penial openings separated by 4% of sternal width.

Pleopod 1 exopod 2.2¥ LW, distally narrowly rounded with strongly oblique medial margin, lateral margin distally concave, medial margin strongly convex (distally narrowed), with PMS from base; endopod 2¥ LW, distally subtruncate, lateral margin sinuate (widest distally, proximally concave), with PMS from 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 bluntly rounded. Endopods of pleopods 3–5 each with mediodistal point (small); pleopods 2–5 peduncle distolateral margin without prominent acute RS.

Uropod peduncle ventrolateral margin with 3 RS, posterior lobe about 0.6¥ 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 two-thirds along ramus, proximal lateral margin with 3 RS, distal lateral margin with 4 RS, medial margin weakly convex, with 6 RS. Exopod extending beyond end of endopod, 2.7 times as long as greatest width, apically not bifid; lateral margin weakly convex, with 12 RS; medial margin convex, with 6 RS.

Female

Similar to males.

Size

Males 21–39 mm (mean = 30 mm), females 26–36 mm (mean = 33 mm); no ovigerous females present in the material examined.

Variation

Robust setae: pleotelson without RS. Several uropodal rami were damaged, so the total number counted varies and is given for each margin. Uropod exopod medial margin (n = 23) 4 (13%), 5 (22%), 6 (52%) and 7 (13%), lateral margin (n = 18) 11 (33%), 12 (50%), 13 (11%); uropod endopod (n = 23) medial margin 5 (22%), 6 (22%) or 7 (13%), lateral margin with 2 + 4 (22%), 3 + 4 (17%), 2 + 5 (26%) and 3 + 5 (35%). There is no discernible difference between males and females, nor does the number of RS increase with the size of the specimen. Of 13 specimens counted only 2 had symmetrical RS for the lateral margin of the endopod for both rami.

P1–3 had slightly variable counts for the RS on the inferior margin of the merus: P1 had 6 + 2 (74%), P2 had 11–15, with 11 (35%) and 12 (45%) most frequent, P3 had 13–15, with 13 (39%) and 14 (44%) most frequent.

Remarks

The huge united eyes with almost no anterior free space between the eyes and the rostrum separates A. musorstom sp. nov. from most others of the genus. Aega musorstom can be separated from similar large- eyed species by the large rectilinear blade on the palm of pereopods 1–3, together with the ovate frontal lamina, long robust setae on the merus of pereopod 1, long acute robust setae on the inferior margin of the ischium of pereopods 2 and 3, long acute robust setae on the ischium-carpus of pereopods 5–7, the uropodal exopod being distinctly larger than the endopod, the uropod endopod with a shallow excision and the pleotelson posterior margin lacking robust setae.

Aega trulla sp. nov., also from the tropical southwestern Pacific, has even larger eyes and a similar propodal blade on pereopods 1–3, but is readily separated by the rounded coxae on pereonites 2 and 3 and the presence of robust setae on the pleotelson.

The very similar and fully sympatric (both species were taken together at one station) A. rickbruscai is readily separated 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. See remarks for that species.

Prey

Only one fish association noted: ‘ Synagonopi sp. 1’, probably a species of Synagrops Günther, 1887 (Acropomatidae) .

Distribution

All records in the vicinity of western New Caledonia including the Coral Sea region of the Chesterfield Archipelago and the Loyalty Islands; at depths from 475 to 615 m.

Etymology

Named in honour of MUSORSTOM, the collecting programme. Its staff have made a major contribution to knowledge of the marine fauna of the region; noun in apposition.

Figures

Figure 35. Aega musorstom sp. nov. A–F, holotype, remainder ♂ paratype 35 mm. A, dorsal view. B, lateral view. C, head, dorsal view. D, frons. E, pleotelson apex, ventral view. F, sternite 7 showing penial openings. G, antennule. H, antenna.

Figure 36. Aega musorstom sp. nov. Paratype ♂ 35 mm. A, mandible. B, mandible palp article 3 detail. C, maxillule apex. D, maxillule. E, maxilla. F, maxilla apex. G, maxilliped. H, maxilliped palp articles 2–5. I, maxilliped palp article 5.

Figure 37. Aega musorstom sp. nov. A, holotype, remainder ♂ paratype 35 mm. A–C, pereopods 1–3, respectively.

Figure 38. Aega musorstom sp. nov. Paratype ♂ 35 mm. A, pereopod 6. B, pereopod 7.

Figure 39. Aega musorstom sp. nov. A, B, holotype, remainder ♂ paratype 35 mm. A, pleopod 1 and detail of coupling hooks. B, pleopod 2. C, uropod. D, uropod exopod, ventral view. E, uropodal exopod, apex. F, uropod endopod, apex.

Figure 64. Distributions of: Aega musorstom sp. nov. (•), A. trulla sp. nov. (*), A. umpara sp. nov. (O) and A. warna sp. nov. (-).