Aega birubi, 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 : 166-171

AEGA BIRUBI SP. NOV. ( FIGS 18–21 , 63 )

Aega antillensis – Hale, 1940: 176, fig. 24e (part), 24h.

Material examined

Holotype: ♂ (26 mm), off Bermagui, NSW, 5.ix. 1994, 200 m, SS05/94/148, coll. P.B. Berents on Southern Surveyor ( AM P43968).

Paratypes: ♀ (non-ovig. 26 mm), East of Broken Bay , NSW, 33∞39¢S, 151∞53¢E, 14.x. 1978, 274 m, coll. FRV Kapala ( AM P34712) . 2♀ (non-ovig. 37, 39 mm), off Botany Bay , NSW, 151∞43¢E, 34∞00¢S, 6.xi. 1972, 731 m, coll. FRV Kapala ( AM P19391) . ♀ (24 mm), 36∞22.6¢S, 150∞14.9¢E, east of Bermagui , NSW, 8.ix.1994, 123– 277 m, sledge ( AM P43970) . ♀ (not measured) off Green Cape to Cape Howe, 37∞22–33¢S, 150∞17–20¢E, 18.iii. 1977, 329 m, coll. FRV Kapala ( AM P43974) . ♀ (non-ovig. 28 mm), Bass Strait , 27.viii.1994, sled, 120 m ( AM P43967) . ♂ (29 mm) Tasmania, Australia, 182 m, C. Hedley, old collections, previously dissected ( Hale, 1940) (no other data) ( AM P9588 ) .

Non-type: ♀ (non-ovig. 34 mm), Cook Strait, 14.ii. 2000, 165 m, off cheek of barracouta (Thyristes atun), coll. Pierce Black ( NMNZ Cr.9949) .

Description

Body 2.8 times as long as greatest width, dorsal surfaces sparsely punctate, widest at pereonite 5, lateral margins weakly ovate. Rostral point projecting anteriorly, not ventrally folded. Eyes large, not medially united, separated by less than 1% width of head; each eye made up of ~21 transverse rows of ommatidia, each row with ~9 ommatidia; eye colour pale brown. Pereonite 1 and coxae 2–3 each with posteroventral 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 times as long as anterior width, dorsal surface without longitudinal carina; lateral margins convex, smooth, posterior margin with elongate medial point, with 6–8 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 2.7¥ LW; flagellum with 8 articles, extending to mid-point of eye. Antenna peduncle article 2 inferior surface without distinct longitudinal suture; article 4 2¥ LW, 1.4 times as long as combined lengths of articles 1–3, with 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, 2.5¥ LW, inferior margin with 1 plumose setae, anterodistal angle with cluster of 2 short simple setae; flagellum with 14 articles, extending to middle of pereonite 1.

Frontal lamina flat, as wide as 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 5 distolateral setae, palp article 3 with 23 setae. Maxillule with 8 terminal RS (falcate). Maxilla medial lobe with 3 RS; lateral lobe with 3 RS (hooked). Maxilliped endite with 1 apical seta; palp article 2 with 3 RS; article 3 with 6 recurved RS (5 hooked, 1 straight); article 4 with 5 hooked RS; article 5 wholly fused to article 4, with 4 RS (3 straight, 1 hooked).

Pereopod 1 basis 2.4 times as long as greatest width; ischium 0.6¥ 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 (acute); carpus 0.5¥ L merus, inferior margin with 0 RS (with small lobe); propodus 1.4 times as long as proximal width, inferior margin with 0 RS, propodal palm with large distal lobe, dactylus smoothly curved, 1.7¥ L propodus. P2 ischium inferior margin with 2 RS (distal), superior distal margin with 2 RS; merus inferior margin with 6 RS (distal 2 on low lobe), set as single row, 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 propodus without large club-shaped distal RS. P6 similar to P7 (larger, more robust). P7 basis 2.8 times as long as greatest width, inferior margin with 7 palmate setae; ischium 0.6¥ L basis, inferior margin with 6 RS (set as 1, 1, 3 and 1), superior distal angle with 3 RS, inferior distal angle with 3 RS; merus 0.8¥ L ischium, 1.9¥ LW, inferior margin with 4 RS (set as 2 and 2), superior distal angle with 5 RS, inferior distal angle with 5 RS; carpus 0.8¥ L ischium, 2.6¥ LW, inferior margin with 2 RS (single cluster), superior distal angle with 4 RS, inferior distal angle with 6 RS; propodus 0.7¥ L ischium, 4.5¥ LW, inferior margin with 2 RS (single cluster), 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 11% of sternal width.

Pleopod 1 exopod 1.9¥ LW, distally narrowly rounded with strongly oblique medial margin, lateral margin straight, medial margin strongly convex, with PMS from base; endopod 2.2¥ LW, distally subtruncate, lateral margin sinuate (widest subdistally, proximally concave), with PMS from distal one-third, medial margin with PMS from distal one-third; peduncle 1.5¥ WL, medial margin with 9 coupling hooks. Pleopod 2 appendix masculina with straight margins, 0.9¥ L endopod, distally bluntly 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 1 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. Endopod apically not bifid, lateral margin proximally convex, distally straight, with prominent excision positioned about three-quarters along ramus, proximal lateral margin with 3 RS, distal lateral margin with 4 RS, medial margin weakly convex, with 5 RS. Exopod extending beyond end of endopod, 3 times as long as greatest width, apically not bifid; lateral margin weakly convex, with 10 RS; medial margin sinuate, proximally concave, with 4 RS.

Female

Similar to male, with exception of the sexual characters.

Variation

Robust setae: all of the 5 specimens examined had some damage to the pleotelson apex. The number of RS is indicative of a range from 3 + 3 to 4 + 4. The uropod apices of most species have nearly all received some damage, particularly to the endopods The numbers are probably lower than actuality. Uropod exopod (n = 12) medial margin with 2–5, with 4 (42%) or 5 (25%) most frequent, lateral margin 8–10 with 9 (50%) or 10 (42%) most frequent; uropod endopod medial margin (n = 10) varied from 2 to 5, with 4 (50%) and 5 (40%) most frequent, the lateral margin (n = 10) RS with 2 + 4 (30%), 3 + 4 (60%) and 4 + 4 (once). 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 (all); P2 merus with 3 + 2 (50%) and 4 + 2 (50%); P3 merus with 4 + 2 (91%), 3 + 2 occurring once.

The eyes are consistently just separated with the exception of a single specimen, that of Hale from Tasmania ( AM P9588), in which a few ommatidia are just making contact at the mid-point. That specimen otherwise agrees well with this species and this difference is slight.

Size

Males 26 and 29 mm, females 26–39 mm (mean = 31.2 mm); no ovigerous females present in the material examined.

Remarks

Aega birubi sp. nov. belongs to a group of closely similar species that includes A. alazon sp. nov., A. umpara sp. nov. in the south-west Pacific, A. kwazulu sp. nov., in the south-western Indian Ocean and A. antillensis in the Caribbean. Aega birubi can be distinguished from all these species by the eyes, which are narrowly separated to just making contact (one specimen), a more strongly convex pleotelson posterolateral margin and most notably the palm of pereopods 1–3 being carinate with a distinct curved and acute small distal lobe. In A. birubi the setae at the distal angles of the pereopod 7 ischium are more robust than those of A. alazon .

Appendage descriptions have been taken from the Bass Strait female ( AM P43967) as all of the specimens closer to the type location had some damage to the uropod apices or anterior pereopods, and the female from Broken Bay ( AM P43712) appears to have partially dried out at some point.

Prey

The only record is from a line-caught barracouta, Thyristes atun (Euphrasen, 1791).

Distribution

South-western Pacific : eastern Australian coast from Broken Bay , New South Wales to Tasmania, to the Cook Strait, New Zealand; at depths between 120 and 731 m.

Etymology

Birubi is an Aboriginal name for the Southern Cross constellation; noun in apposition.

Figures

Figure 18. Aega birubi sp. nov. A–G, holotype. H–J, paratype (AM P43967). A, dorsal view. B, lateral view. C, head, dorsal view. D, frons. E, pereopod 1 (in situ). F, pereopod 2 (in situ). G, sternite 7 showing penial openings. H, antenna dorsal view. I, antenna, peduncle articles 1–3, ventral view. J, antennule.

Figure 19. Aega birubi sp. nov. Paratype (AM P43967). A, mandible. B, mandible palp article 3 detail. C, maxillule. D, maxillule mesial lobe. E, maxillule lateral lobe, apex. F, maxilla. G, maxilla apex, detail. H, maxilliped. I, maxilliped palp article 5. J, maxilliped palp articles 2–5.

Figure 20. Aega birubi sp. nov. Paratype (AM P43967). A–D, pereopods 1, 2, 6 and 7, respectively.

Figure 21. Aega birubi sp. nov. A, B, holotype, remainder paratype (AM P43967). A–E, pleopods 1–5, respectively. F, uropod. G, uropod exopod, ventral view. H, uropod endopod, 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).