Aega magnifica, (DANA, 1853)

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 : 220-229

AEGA MAGNIFICA ( DANA, 1853) ( FIGS 57–60 )

Pterelas magnificus Dana, 1853: 769 ; 1853 (Atlas), pl. 51, fig. 4a–g.

AEga magnifica – Schioedte & Meinert, 1879: 363, pl. 8, figs 14-19.

Aega magnifica – Bovallius, 1885: 8, pl. 2, figs 11–17; Dollfus, 1891: F56, pl. 8, fig. 1, 1b; Giambiagi, 1925: 233; Menzies, 1962: 117, fig. 38D–I.

Aega (Aega) magnifica – Brusca, 1983: 9, 11.

Material examined

Neotype (here designated): ♂ (18.5 mm), Bahia Inutil (c. 53∞37¢S, 69∞36¢W), Patagonian Archipelago , 23.i.1896, stn 626, 36– 55 m, shell debris, collected by Nordenskjöld’s Expedition till Eldslandet och Patagonien, 1895–96 ( SMNH 5907 ).

Non-type material: LUND UNIVERSITY CHILE EXPEDITION 1948–49 ( Menzies, 1962): 2 ♀ (non-ovig. 29, 30 mm) , Golfo de Ancud , Estero Huito, central part, 41∞43.83¢S, 73∞10.25¢W, 5.xii.1948, stn M20, very fine sand mixed with mud, 15 m ( SMNH 46250 ); ♀

(ovig. 28 mm, with 2 mancas), Golfo de Ancud, Canal Calbuco, between Punta Meimen and Punta, 41∞48.83¢S, 73∞09.67¢W, 15.xii.1948, stn M21, small stones, 25 m ( SMNH 46249); ♀ (non-ovig. ~ 19 mm, previously dissected, in 2 pieces, one P1 missing), Golfo de Ancud , between Isla Quenu and Isla Chidguapi, 41∞49.67¢S, 73∞10.00¢W, 3.v.1949, stn M27, coarse sand with shells, 45 m ( SMNH 46248 ) ; ♀ (non-ovig. 23 mm), Golfo de Ancud , south of Isla Quellin, from rocks, vii.1949 ( SMNH 46251 ). (All coordinates converted to decimal degrees to 2 places.) EUGENIE EXPEDITION: 3 ♀ (non-ovig. 18, 20, 21 mm), Magellan Strait , Atlantic, coll. Eugenie Expedition 1851– 1853 (no other data but ‘det. H.J. Hansen’) ( SMNH 46239 ) ; ♀ (non-ovig. 25 mm), Magellan Strait , Atlantic, without station number (‘utan nummer’), coll. Eugenie Expedition 1851–1853 ( SMNH 46240 ) ( Bovallius, 1885, reported one specimen from this expedition) . NORDENSKJÖLD’S EXPEDITION till Eldslandet och Patagonien, 1895–96 : 2 ♀ (non-ovig. 23 mm, ovig. 22 mm, both somewhat anteriorly posteriorly crushed), Punta Arenas, Patagonian Archipelago, 5.xii.1895, stn 341, shell debris ( SMNH 46247 ) . 3 specimens (19, ~20, ~ 17 mm, all damaged), Bahia Inutil , Patagonian Archipelago, 23.i.1896, stn 63718, 27 m, shell debris ( SMNH 46243 ) . Manca (9.5 mm), Voilier Cove, Patagonia, 54∞53¢S, 69∞38¢W, 2.ii.1896, 18 m, sand and mud ( SMNH 46244 ) . ♂ (10.5 mm), Katanashuaia , Patagonia , channel between Oste and ??, 28 May? 1896 (stn 189), 18–22 m, stones and shell debris

( SMNH 46245). SVENSKA SUDOLAR EXPEDITION 1901–03: ♀ (non-ovig. 21 mm, partly dissected, appendages missing), Patagonian Archipelago , the east inlet of the Beagle Channel , 55∞10¢S, 66∞15¢W, 15.ix. 1902, 100 m, broken shells ( SMNH 46241 ). SWE- DISCHE EXPEDITION NACH DEN MAGEL- LANSLÄNDERN 1907–09: ♂ (19.0 mm), Otway Water, Pto Toro, Argentina, 15.iv.1908, 20– 30 m stones and shell debris ( SMNH 46246 ). MISSION SCIENTI- FIQUE DU CAP HORN. 1882–1883 (reported by Dollfus, 1891): ♂ (22 mm), ♀ (non-ovig. 28 mm), Baie Orange, Mis. Cap Horn 59–96 ( MNHN Is.2446). ♀? (21 mm), Baie Orange, Mis. Cap Horn ( MNHN Is.2447). ♂ (~ 16 mm), ♀ (ovig. ~ 23 mm), poor condition, dried out at some time in the past, no collection details ( MNHN Is.2448) .

Other material: ♀ (non-ovig. 17.5 mm), Straits of Magellan , ‘ Ichthye’ Kr. [part of Schioedte & Meinert’s (1879) material] ( ZMUC old collection, unreg.) . ♀ (ovig. 24 mm), manca (9.8 mm) off Gulf of San Mation, Patagonia, Argentina, Argentina, Rio Negro, U.S. Fish Commission Steamer Albatross stn 2768, 79 m ( USNM 22667 ) . ♀ (non-ovig. 33 mm), off coast off Patagonia, Argentina, U.S. Fish Commission Steamer Albatross stn 2770, 106 m ( USNM 22668 ) . ♀ (nonovig. not measured), Patagonian Shelf, 46∞19.0–17.5¢S, 65∞0.0–4.5¢W, 3.xi.1931, 107– 99 m, Discovery stn WS776 ( BMNH 2003.12 ) ; also 3 (2 and manca) Discovery stn WS776 (BMNH, 2003.13–15). ♀ (non-ovig. not measured), Patagonian Shelf, 47∞50.3¢S, 63∞57.0¢W, 20.iii.1931, 101– 114 m, Discovery stn WS797 ( BMNH 2003.16 ) . 1, Patagonian Shelf, 51∞44.5–46.0¢S, 66∞38.0–42.0¢W, 13.i.1931, 111– 118 m, Discovery stn 814 ( BMNH 2003.10 ) .

Type locality

That of neotype, namely Bahia Inutil , Fuegia, Chile, c. 53∞37¢S, 69∞36¢ W. Dana’s type locality was given only as ‘ Nassau Bay, Fuegia’ (Cape Horn, Chile). This location is approximately 54∞S, 68∞W (part of Isla de Navarino) .

Description

Body 2.5 times as long as greatest width, dorsal surfaces smooth, widest at pereonite 6, lateral margins subparallel. Rostral point projecting anteriorly, not ventrally folded. Eyes small, combined widths less than 50% width of head, separated by about 38% width of head; each eye made up of ~13 transverse rows of ommatidia, each row with ~8 ommatidia; eye colour black. Pereonite 1 and coxae 2–3 each with posteroventral angle rounded, or 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 to but not beyond posterior margin of pleonite 5; 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 carina; lateral margins sinuate (weakly), smooth, posterior margin converging to caudomedial point, with 14 RS.

Antennule peduncle articles 1 and 2 flattened, article 2 anterodistal lobe not extending beyond mid-point of article 3 (with blade-like anterior margins); articles 3 and 4 0.7 times as long as combined lengths of articles 1 and 2, article 3 2.2¥ LW; flagellum with 13 articles, extending to anterior of pereonite 1. Antenna peduncle article 2 inferior surface with distinct longitudinal suture; article 4 1.5¥ LW, 1.0 times as long as combined lengths of articles 1–3, without deep longitudinal groove, inferior margin with 0 plumose and 0 short simple setae; article 5 not markedly wider or flatter than article 4, 1.1¥ L article 4, 2.1¥ LW, inferior margin with 7 plumose setae, anterodistal angle with cluster of 2 short simple setae (plumose); flagellum with 22 articles, extending to middle of pereonite 3.

Frontal lamina flat, wider than long, lateral margins parallel, anterior margin rounded, with small median point, posterior margin not abutting clypeus.

Mandible molar process absent; palp article 2 with 13 distolateral setae (biserrate, plus 3 simple submarginal), palp article 3 with 27 setae. Maxillule with 7 terminal RS (3 large, 4 small and slender). Maxilla medial lobe with 3 RS (2 biserrate); lateral lobe with 3 RS. Maxilliped endite with 2 apical seta; palp article 2 with 5 RS (straight); article 3 with 7 recurved RS (5 hooked, 1 long and 1 short straight); article 4 with 5 hooked RS (4 large, 1 small); article 5 partly fused to article 4, with 4 RS (2 straight, 2 curved).

Pereopod 1 basis 2.1 times as long as greatest width (widest basally); ischium 0.4¥ L basis, inferior margin with 0 RS (with 1 subdistal seta), superior distal margin with 2 RS; merus inferior margin with 3 RS, set as distal group (plus 1 slender seta), superior distal angle with 1 RS (small); carpus 0.6¥ L merus, inferior margin with 0 RS; propodus 1.3 times as long as proximal width, inferior margin with 0 RS, propodal palm with distal blade, dactylus smoothly curved, 2.1 L propodus. P2 ischium inferior margin with 0 RS (with subdistal slender seta), superior distal margin with 2 RS; merus inferior margin with 11 RS, set as in 2 groups (row of 9 with distal pair set dorsal to row), superior distal margin with 1 acute RS; carpus similar in size to that of P1, inferodistal angle with 1 RS (small), propodus without large club-shaped distal RS. P3 similar to P2; propodus without large clubshaped distal RS. P6 similar to P7. P7 basis 2.9 times as long as greatest width, inferior margin with 12 palmate setae; ischium 0.6¥ L basis, inferior margin with 7 small RS (set as 1, 1, 1, 1 and 3), superior distal angle with 4 RS, inferior distal angle with 7 RS; merus 0.9¥ L ischium, 2.5¥ LW, inferior margin with 7 RS (set as 1, 2 and 4), superior distal angle with 13 RS, inferior distal angle with 7 RS; carpus 1.0¥ L ischium, 3.1¥ LW, inferior margin with 4 RS (set as 1 and 3), superior distal angle with 7 RS, inferior distal angle with 7 RS; propodus 0.8¥ L ischium, 4¥ LW, inferior margin with 3 RS (set as 1, 2 and 1), superior distal angle with 3 slender setae (2 simple, 1 palmate), inferior distal angle with 4 RS.

Penes opening flush with surface of sternite 7; penial openings separated by 10% of sternal width.

Pleopod 1 exopod 2.1¥ LW, distally narrowly rounded, medial margin weakly oblique, lateral margin straight, medial margin strongly convex, with PMS from distal half; endopod 2.1¥ LW, distally subtruncate, lateral margin strongly concave, with PMS from distal margin only, medial margin with PMS from distal half; peduncle 1.7¥ WL, medial margin with 10 coupling hooks. Pleopod 2 appendix masculina with straight margins, 0.9¥ 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 with endopod and exopod coplanar (weakly oblique), rami extending to pleotelson apex, marginal setae dense, in several tiers (weakly so), apices acute. Endopod apically subbifid, medial process prominent, lateral margin proximally convex or distally straight, without prominent excision, proximal lateral margin with 2 RS, distal lateral margin with 2 RS, medial margin straight, with 6 RS. Exopod not extending to end of endopod, 3.6 times as long as greatest width, apically not bifid; lateral margin weakly convex, with 10 RS; medial margin straight, distally convex, with 2 RS.

Variation

Robust setae: many specimens have some degree of damage to the pleotelson apex, therefore only the ranges for RS are indicative. Pleotelson (n = 10) 12–14 RS with 12 (50%) most frequent, 13 (30%) and 7 + 7 (20%). Uropod exopod medial margin (n = 15) with 2 (80%) or 3 (30%) RS, lateral margin (n = 14) with from 9 to 12, with 10 (42.8%) and 11 (50%) most frequent; uropod endopod (n = 21) medial margin varied from 5 to 7, with 5 (80.9%) most frequent 6 (14.3%) and 7 once, lateral margin usually with 2 + 2 (71.4%) also 1 + 1 (once), 2 + 3 (twice) and 3 + 2 (3 times).

Pereopod RS are highly consistent with the merus of P1 (n = 25) with a distal row of 3 (100%); P2 merus (n = 26) with 7 + 2 (69.2%), 8 + 2 (26.9%) and 9 + 2 (once); and P3 merus (n = 27) with 9 + 2 (77.8%) most frequent, with 8 + 2, 9 + 3, 10 + 2 and 10 + 3 all occurring at least once.

Colour pattern is rarely recorded for aegids in large part due to the lack of patterning. Most of the specimens examined here have, despite their age, a persistent pattern of dark brown patches on the lateral margin of pereonites (most noticeable on pereonites 5, 6 and 7) and on the anterolateral corners of the pleotelson; there is some colour on the coxae but this is weaker than that shown on the pereonites and pleotelson.

Size

Males (n = 5) 10.5–22 mm, mean 17.2 mm; nonovigerous females (n = 11) 18–29 mm, mean 22.8 mm;

ovigerous females (n = 3) 22–28 mm, mean 24.3 mm (3 damaged specimens omitted from calculations).

Remarks

This species is excluded from the A. deshaysiana group by having relatively small eyes, uropods that extend to just beyond the posterior margin of the pleotelson, margins of the uropodal rami provided with a dense multitiered row of plumose marginal setae, and coplanar uropodal rami. In addition, the anterior margins of the antennule peduncle articles 1 and 2 are anteriorly expanded with a blade-like edge.

Species recognition is easily made on the basis of the relatively small eyes in conjunction with pereopods 1–3 having a large propodal blade and the shape of the coxae of pereonites 2 and 3 which have a somewhat lobate posterodorsal margin; the setation of the anterior pereopods is characteristic and distinctive in that on the inferior margin of pereopod 1 merus there is a distal cluster of 3 robust setae, there being no robust setae proximal to these, and on the inferior margin of the merus of pereopods 2 and 4 there is a ventral row of robust setae with a distal pair of setae set more dorsally. Confirmation of identity can be made using the shape and setation of the pleotelson and uropods.

Aega falklandica Kussakin, 1967 , is perhaps the most similar species to A. magnifica , and there is the potential that these two species have distributions that overlap. Aega falklandica is readily separated from A. magnifica , as are all other species of Aega known from the South Atlantic, by the lack of a prominent propodal blade on the propodus of pereopods 1–3. The status of A. falklandica in relation to A. punctulata Miers, 1881 (‘from the Straits of Magellan’) and A. edwardsi Dollfus, 1891 (Orange Bay, Cape Horn) is entirely uncertain given that all three of these species are in need of redescription and clearly lack a blade or lobe on the propodal palm of pereopods 1–3. Aega punctulata is described by Miers (1881) as having the posterior segments covered in setae.

It is well known that Dana’s South Pacific crustacean type material ‘was lost on the fatal bar’ when the sloop Peacock sank at the mouth of the Colombia River in 1841 (information from a hand-written account from Dana’s note books, dated 1857, of the fate of his material). Most of this material was from the tropical and equatorial Pacific, and while Dana’s notes do not mention that the Fuegian material was lost there has never been any evidence to suggest that any isopod types survived the disaster. The subsequent records of A. magnifica are consistent, and the species differs from all others by virtue of the spoonshaped blade on the propodus of pereopod 1 together with the relatively small eyes. Given that there are other species that are similar A. magnifica , that this name has priority over most others, that it is now apparent that there are groups of morphologically very similar species within the genus Aega , and that although many species have restricted ranges, others (such as A. monophthalma [see Bruce, 2001] and A. alazon sp. nov., to name two) have extensive, possibly global, distributions, I have designated a neotype for A. magnifica ( Dana, 1853) .

Prey

No records. Distribution

Southern South America in the Atlantic region of the Straits of Magellan , Tierra del Fuego, to 41∞S in the Chilean Pacific ; recorded depths between 10 and 118 m.

Figures

Figure 57. Aega magnifica (Dana, 1853). Neotype. A, dorsal view. B, lateral view. C, head, dorsal view. D, frons. E, pleonite, lateral view. F, sternite 7 showing penial openings. G, frontal margin if head in anterior view. H, antennule. I, antennule peduncle, articles 1 and 2, ventral view. J, antenna peduncle, articles 1–3, ventral view. K, antenna.

Figure 58. Aega magnifica (Dana, 1853). Female, SMNZ46250. A, mandible. B, mandible palp article 3. C maxillule. D, maxillule apex. E, maxilla. F, maxilla, apex detail. G, maxilliped. H, maxilliped palp article 5, dorsal view. I, maxilliped palp articles 2–4.

Figure 59. Aega magnifica (Dana, 1853). Neotype. A–C, pereopods 1, 2 and 7, respectively. D, pereopod 1, ischium superior distal angle. E, posterior margin of pleotelson.

Figure 60. Aega magnifica (Dana, 1853). A, B and F, neotype, remainder female, SMNZ46250. A–E, pleopods 1–5, respectively. F, pleopod 1 peduncle, mesial margin, dorsal view. G, uropod. H, uropod exopod, ventral view. I uropod exopod apex. J, uropod endopod apex.