Aega alazon, 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 : 156-162

AEGA ALAZON SP. NOV. ( FIGS 12–15 , 62 )

? Rocinela Deshayesiana – Studer, 1884: 22.

Aega antillensis – Hale, 1925: 176 (part); 1929: 254, fig. 248 (part); Kensley, 1975: 39; 1978, fig. 24A, B, 2001: 226 (part).

Aega deshayesiana – Nierstrasz, 1918: 108; 1931: 182 (part).

Aega ‘antillensis’ – Kensley, 1976: 290.

Aega deshaysiana – Nierstrasz, 1931: 182 (part); Hale, 1940: 295 (part, Gabo Is.); Sivertsen & Holthuis, 1980: 33; Kensley, 2001: 226 (part).

Material examined

Holotype: ♀ (57 mm), south of Port Elizabeth , South Africa, 34∞24.5¢S, 26∞12.7¢E, 12.x. 1992, 545 m, midwater trawl, coll. RV Africana (SAfM A43115).

Paratypes: 2 ♀ (51, 58 mm), south of Still Bay , South Africa, 35∞27¢S, 21∞40¢E, 28.v. 1988, 127 m, bottom trawl, coll. RV Africana (SAfM A43114 ) . ♀ (54 mm), south of Still Bay , South Africa, 35∞17¢S, 21∞32¢E, 27.v. 1988, 116 m, bottom trawl, coll. RV Africana (SAfM A43113 ) . ♂ (31 mm), imm (26 mm), off Cape Town , South Africa, 20.vi.1972, SST 84.A, coll. University of Cape Town Ecological Survey (SAfM A14622 ) ( Kensley, 1975?).

Non types. INDIAN OCEAN: ♀ (42 mm), Saint Paul Is , 4.i.1971, on Thyristes, coll. R. Vranchex ( MNHN Is. 2355) ( Kensley, 1976) ; ♀ (33 mm), Saint Paul Is , 4.i.1971, coll. R. Vranchex ( MNHN Is. 2356) ( Kensley, 1976) ; ♀ (49 mm), near Seychelles ( ZMA) ( Nierstrasz, 1918); SOUTH ATLANTIC : ♀ (33 mm), Tristan da Cunha Island, 13.i.1938, in a fishing boat ( University of Trondheim , Norway) ( Sivertsen & Holthuis, 1980). AUSTRALIA : ♀ (33 mm), Tasmania, 40∞58.20¢S, 143∞49.00¢E, 26.i. 1985, 550 m, coll. CSIRO R.V. Soela ( NMV J27710 ) . ♀ (33 mm), 37∞34¢S, 149∞55¢E, off Gabo Is., Vic , 8.xi. 1912, 146 m ( AM E4763 ) ( Hale, 1940) . ♂ (small, not measured), off Gabo Is., Vic , 366 m ( AM E4837 ) ( Hale, 1940) . ♀ (non-ovig. 47 mm), Fowlers Bay , South Australia (c. 31∞58¢S, 132∞35¢E), on large basking shark ( Cetorhinus maximus ), coll. C.A. Tait ( SAM C113 ) ( Hale, 1925) . ♀ (41 mm), 22 nm SSW of Cape Martin , South Australia, 37∞46.69¢S, 139∞42.99¢E, 15.xii.1987, 290– 350 m, trawled, coll. K. Gowlett-Holmes, T. Moran & P. Reilly ( SAM TC13990 ) . ♀ (38 mm), 23 nm SSW of Cape Martin , South Australia, 37∞50.71¢S, 139∞50.11¢E, 15.xii.1987, 150– 170 m, trawled, coll. K.L. Gowlett-Holmes, T. Moran & P. Reilly ( SAM TC13991 ) . ♀ (46 mm), south of Beachport , South Australia, 37∞45.00¢S, 139∞41.00¢E, 24.x. 1981, 370 m, coll. R. Wilson ( NMV J27713 ). NEW ZEALAND : ♀ (26 mm), off south-western South Island , 46∞29.1¢S, 166∞34.0¢E, 17.xi. 1986, 460 m, on skin of Genypterus blacodes , coll. B. Jones, FRD ( NMNZ Cr. 9264) . ♂ (29 mm), off south-western South Island , 47∞43.4¢S 167∞18.7¢E, 15.xi. 1986, 145 m, pectoral fin of Rexea solandri , coll. B. Jones ( NMNZ Cr. 9266) . 2 ♂ (32, 38 mm), ♀ (29 mm), North Otago, South Island , 1962, 45.7 m (as 25 fms), coll. J. Graham ( NMNZ Cr. 9263) . ♀ (56 mm), Oamaru, South Island , 4.i.1969, on dogfish, 73 m ( NMNZ Cr. 9267) . ♀ (56 mm), Pukaki Rise , off skate egg case of Bathyraja sp. (no other data), coll. J. Graham ( NMNZ Cr. 4968). NEW CALEDONIA : ♀ (23 mm), 23∞38.35¢S, 167∞42.68¢E, 30.x.1986, stn DW 77, 435 m, coll. MUSORSTOM ( MNHN Is. 5796) .

I have not seen the specimen identified as A. antillensis (cat. no. SST.84.A, 200 m, Still Bay, c. 35∞S, 22∞E) by Kensley (1975), presumably held at the Zoology Department, University of Cape Town.

Description

Body 2.8 times as long as greatest width, dorsal surfaces smooth, widest at pereonite 5, lateral margins subparallel. Rostral point projecting anteriorly, not ventrally folded. Eyes large, medially united, anterior clear field 21% length of head, posterior clear field 46% length of head; each eye made up of ~22 transverse rows of ommatidia, each row with ~9 ommatidia; eye colour dark brown. Pereonite 1 and coxae 2–3 each with posteroventral angle right-angled; 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– 1.2 times as long as anterior width, dorsal surface without longitudinal carina; lateral margins convex, smooth, posterior margin with elongate medial point, with 6–10 RS (?).

Antennule peduncle articles 1 and 2 flattened, article 2 anterodistal lobe not extending beyond mid-point of article 3; articles 3 and 4 0.7 times as long as combined lengths of articles 1 and 2, article 3 2.7¥ LW; flagellum with 9 articles, extending to posterior margin of eye. Antenna peduncle article 2 inferior surface with indistinct groove; article 4 1.9¥ LW, 1.3 times as long as combined lengths of articles 1–3, without deep longitudinal groove, inferior margin with 1 plumose setae, and 0 short simple setae; article 5 not markedly wider or flatter than article 4, 1.0¥ L article 4, 2.6¥ LW, inferior margin with 1 plumose seta, anterodistal angle with cluster of 2 short simple setae; flagellum with 19 articles, extending to posterior of pereonite 1.

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

Mandible molar process absent; palp article 2 with 6 distolateral setae, palp article 3 with 34 setae. Maxillule with 8 terminal RS. Maxilla medial lobe with 4 RS; lateral lobe with 3 RS. Maxilliped endite with 1 apical seta; palp article 2 with 4 RS; article 3 with 5 recurved RS (and 1 simple seta); article 4 with 6 hooked RS; article 5 partly fused to article 4, with 5 RS (2 recurved, 3 straight).

Pereopod 1 basis 2.1 times as long as greatest width; ischium 0.5¥ L basis, inferior margin with 0 RS, superior distal margin with 2 RS (acute); merus inferior margin with 3 RS, set as 2 groups (of 1 and 2), superior distal angle with 2 RS (slender); carpus 0.9¥ L merus, inferior margin with 0 RS; propodus 1.8 times as long as proximal width, inferior margin with 0 RS, propodal palm with small distal lobe, dactylus smoothly curved, 1.2¥ L propodus. P2 ischium inferior margin with 1 RS (distal), superior distal margin with 1 RS; merus inferior margin with 5 RS, set as 2 groups (of 3 and 2), superior distal margin with 2 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 (merus with single row of 7 RS); propodus without large club-shaped distal RS. P6 similar to P7 (with longer RS on inferior margin). P7 basis 2.9 times as long as greatest width, inferior margin with 6 palmate setae (or more); ischium 0.6¥ L basis, inferior margin with 5 RS (set as 1, 2 and 2), superior distal angle with 7 RS, inferior distal angle with 5 RS; merus 0.9¥ L ischium, 2.6¥ LW, inferior margin with 4 RS (set as 2 and 2), superior distal angle with 5 RS, inferior distal angle with 7 RS; carpus 0.8¥ L ischium, 2.9¥ LW, inferior margin with 2 RS (set as single cluster), superior distal angle with 3 RS, inferior distal angle with 6 RS; propodus 0.7¥ L ischium, 5.8¥ LW, inferior margin with 2 RS (set as single cluster), superior distal angle with 2 slender setae (1 simple, 1 palmate), inferior distal angle with 2 RS.

Pleopod 1 exopod 1.8¥ LW, distally narrowly rounded with strongly oblique medial margin, lateral margin straight (weakly oblique), medial margin strongly convex, with PMS from base; endopod 2¥ LW, distally rounded, lateral margin sinuate, with PMS from distal half, medial margin with PMS from distal half; peduncle 1.8¥ WL, medial margin with 8 coupling hooks. 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 (plus single seta), posterior lobe about one-half 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, with prominent excision positioned about four-fifths along ramus, proximal lateral margin with 2 RS, distal lateral margin with 4 RS, medial margin strongly convex, with 3 RS. Exopod extending beyond end of endopod, 2.8 times as long as greatest width, apically not bifid; lateral margin weakly convex, with 10 RS; medial margin sinuate, proximally concave, with 3 RS.

Male

Similar to female. Penes opening flush with surface of sternite 7; penial openings separated by 5% of sternal width. Appendix masculina with straight margins, 0.74¥ L endopod, distally narrowly rounded.

Variation

Robust setae: of the specimens examined only 2 had a sufficiently intact pleotelson to allow the RS to be counted, indicating a range from 3 + 3 to 4 + 4, perhaps more. Uropod (n = 15) exopod medial margin with 2–4, with 3 (43%) or 4 (47%) most frequent, lateral margin 9 (27%) or 10 (53%); uropod endopod (n = 15) medial margin varied from 2 to 6, with 3 (27%), 4 (40%) and 5 (17%) most frequent, the lateral margin RS are variable with the proximal RS at 2–5, distal RS 3–6, with 3 + 4 (15%), 4 + 4 (27%) and 4 + 5 and 5 + 5 (each 11.5%), 4 + 5 (10%) and 5 + 4 (5%). There is no discernible difference between males and females, nor does the number of RS increase with the size of the specimen.

P1 setation of the merus was consistent across its range with 1 + 2 RS (93%), 2 + 2 occurring only twice; P2 merus ranged from 5 to 7 RS, with 5 (28%) and 6 (65%) most common, 7 occurring twice; P3 merus with 6 (82%) or 7 (21%).

In occasional specimens (e.g. from New Zealand, NMNZ Cr.9267) the eyes are very narrowly separated.

Size

Males 29–38 mm (mean = 23.5 mm), females 21– 58 mm (mean = 37.8 mm); no ovigerous females present in the material examined.

Remarks

One of the most widespread and frequently collected of this group of species, and hence the species most frequently misidentified as A. deshaysiana , A. alazon sp. nov. presents a near consistent appearance throughout its range, though there is variation in the number of robust setae on the merus of the pereopods and on the uropodal endopod. Characters by which the species can be identified include the shape of the weakly lobate antennule peduncle article 2, fully united eyes, the shape of the frontal lamina which has a minute median point, the simple propodus on pereopod 1, the characteristic pattern of robust setae on the merus of pereopod 1 (1 + 2), 2 (2 + 3) and 3 (7 in a single row), the uropodal proportions (exopod longer than endopod, endopod lateral margin with distal part short, anterior part convex) and setation of the uropods which has a relatively distal excision on the endopod and the relatively short pleotelson which has a short median point.

Aega umpara sp. nov. and A. birubi sp. nov. are sympatric with A. alazon over part of their ranges. Aega umpara differs in having a more rectangular frontal lamina, in the disparate sizes of the robust setae on pereopod 1 merus (which are of a similar size in A. alazon ), uropodal exopod lacking PMS on the proximal one-third and the uropodal exopod apex not extending to the uropodal endopod apex (in A. alazon the exopod exceeds the endopod). These differences and some others are discussed in more detail under the remarks for A. umpara . Aega birubi is very similar but smaller and differs most notably in having distinctly carinate palms on pereopods 1–3, a consistently small acute propodal lobe, eyes that are scarcely in contact medially and minor but consistent differences in pereopod setation.

The single female from the Seychelles is provisionally retained under this species as it accords well on most characters. It differs slightly in that the eyes only just meet medially and the frontal lamina is posteriorly slightly wider.

Aega alazon is also very similar to the North Atlantic species A. antillensis , but can be reliably distinguished from that species in having a simple propodal palm on pereopods 1–3 and in the anterodistal angle of antennule peduncle article 2 forming a distinct small lobe.

Prey

Pink cusk-eel, Genypterus blacodes (Forster, 1801) , Ophidiidae ; the snake mackerels Rexea solandri

(Cuvier, 1832) and Thyristes sp., Gempylidae ; basking shark, Cetorhinus maximus (Gunnerus, 1765) .

Distribution

Southern Ocean from the South Atlantic and South Africa to New Zealand, extending northwards into the tropics of the Indian Ocean and south-western Pacific Ocean off the Seychelles and New Caledonia. Given the widespread records in the Indian Ocean , southwestern Pacific and southern South Atlantic, it would seem reasonable to expect this species to be found throughout the Southern Ocean; at depths between 46 and 550 m.

Etymology

Alazon (Greek), meaning wanderer or rover, alluding to the wide Southern Hemisphere distribution of this species.

Figures

Figure 12. Aega alazon sp. nov. A–D, holotype, E–G, ♀ paratype 51 mm (SafM A43114). A, dorsal view. B, lateral view. C, head, dorsal view. D, frons. E, antennule. F, antenna. G, antenna peduncle articles 1–3, ventral view. H, sternite 7 showing penial openings, ♂ paratype (SafM A14622).

Figure 13. Aega alazon sp. nov. Paratype ♀, 51 mm (SafM A43114). A, mandible. B, mandible palp article 3 detail. C, maxillule. D, maxillule apex. E, maxilla. F, maxilla apex, detail. G, maxilliped. H, maxilliped palp article 5. I, maxilliped palp articles 2–5.

Figure 14. Aega alazon sp. nov. A–G, holotype, H, ♀ paratype 51 mm (SafM A43114). A, D–G, pereopods 1, 2, 4, 6 and 7, respectively. B, pereopod 1, medial surface of ischium. C, pereopod 1 dactylus, in perpendicular view. H, pereopod 7.

Figure 15. Aega alazon sp. nov. Paratype ♀, 51 mm (SafM A43114). A–E, pleopods 1–5, respectively. F, pleopod 2, ♂ paratype (SafM A14622). G, uropod, uropod exopod, ventral view. H, uropod.

Figure 62. Distributions of: Aega alazon sp. nov. (•), A. excisa (Δ), A. japonica sp. nov. (*), A. kwazulu sp. nov. (-) and six undescribed species of the A. deshaysiana group (O).