Aega excisa, RICHARDSON, 1910

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 : 151-156

AEGA EXCISA RICHARDSON, 1910 ( FIGS 9–11 , 62 )

Aega excisa Richardson, 1910 : fig. 11.

Aega antillensis –? Shiino, 1965: 543, figs 1–3;? Saito et al. 2000: 59 (part).

Aega deshaysiana – Nierstrasz, 1931: 182 (part); Kensley, 2001: 226 (part).

Material examined

Holotype: ♀ (ovig. 34 mm), off Jolo Light , Philippines, 6∞02.92¢N, 120∞53.00¢E, 5.iii.1908, Albatross stn 5173, 340 m (tube contains label stating ‘examined by R.C. Brusca, 1981’; specimen in poor condition, most posterior legs broken anteriorly; previously dissected.) ( USNM 40912 ).

Non-type: ♀ (non-ovig. 36 mm), Bono-misaki , Japan, 13.v.1914, trawled 16 m, coll. Dr Th. Mortensen’s Pacific Expedition 1914–15 ( ZMUC CRU3878 ) .

Description

Body 2.3 times as long as greatest width, dorsal surfaces smooth, widest at pereonite 4, lateral margins subparallel. Rostral point projecting anteriorly, not ventrally folded. Eyes large, not medially united, separated by about 2% width of head; each eye made up of ~21 transverse rows of ommatidia, each row with ~11 ommatidia; eye colour faded, not known. Pereonite 1 and coxae 2–3 each with posteroventral angle rounded; 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 10 RS.

Antennule peduncle articles 1 and 2 flattened, article 2 without anterodistal lobe; articles 3 and 4 0.8 times as long as combined lengths of articles 1 and 2, article 3 2.9¥ LW; flagellum with 8 articles, extending to mid-point of eye. Antenna peduncle article 2 inferior surface with distinct longitudinal suture; article 4 2.3¥ LW, 1.4 times as long as combined lengths of articles 1–3, with deep longitudinal groove (distal), inferior margin with 0 plumose setae, and 0 short simple setae; article 5 not markedly wider or flatter than article 4, 1.1¥ L article 4, 3.1¥ LW, inferior margin with 0 plumose setae, anterodistal angle with cluster of 2 short simple setae (1 plumose seta); flagellum with 18 articles, extending to middle of pereonite 1.

Frontal lamina flat, longer than greatest width, 1.6¥ LW, lateral margins converging posteriorly, anterior margin rounded (with minute median indentation), without small median point, posterior margin not abutting clypeus.

Mandible molar process present, minute; palp article 2 with 2 distolateral setae, palp article 3 with 28 setae. Maxillule with 8 terminal RS. Maxilla medial lobe with 3 RS (2 hooked, 1 straight); lateral lobe with 4 RS (hooked). Maxilliped endite with 2 apical setae (slender); palp article 2 with 2 RS; article 3 with 5 recurved RS (4 recurved and 1 straight); article 4 with 5 hooked RS; article 5 partly fused to article 4, with 6 RS (2 stout recurved, 4 straight).

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; merus inferior margin with 4 RS, set as 2 groups (of 2 and 2), superior distal angle with 0 RS; carpus 0.5¥ L merus, inferior margin with 0 RS; propodus 1.9 times as long as proximal width, inferior margin with 0 RS, propodal palm with simple, without blade or process, dactylus smoothly curved, 1.1¥ L propodus. P2 ischium inferior margin with 1 RS (distal), superior distal margin with 2 RS; merus inferior margin with 6 RS, 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 similar to P2; propodus without large club-shaped distal RS. P6 similar to P7. P7 basis 2.9 times as long as greatest width, inferior margin with 11 palmate setae; ischium 0.6¥ L basis, inferior margin with 7 RS (set as 1, 1, 3 and 1), superior distal angle with 4 RS, inferior distal angle with 4 RS; merus 0.7¥ L ischium, 2¥ LW, inferior margin with 7 RS (set loosely as 3 and 4), superior distal angle with 9 RS, inferior distal angle with 5 RS; carpus 0.9¥ L ischium, 3.5¥ LW, inferior margin with 5 RS (set as 2 and 3), superior distal angle with 4 RS, inferior distal angle with 4 RS; propodus 0.6¥ L ischium, 5¥ LW, inferior margin with 2 RS (single cluster), superior distal angle with 3 setae (1 RS, 1 plumose and 1 simple), inferior distal angle with 3 RS.

Pleopod 1 exopod 2¥ LW, distally narrowly rounded, medial margin weakly oblique, lateral margin weakly convex, medial margin strongly convex, with PMS from base; distally subtruncate, lateral margin sinuate, with PMS from distal half, medial margin with PMS from distal half; peduncle 1.8¥ WL, medial margin with 9 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 (and long PMS), posterior lobe about two-thirds 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 or distally straight, with prominent excision positioned about three-quarters along ramus, proximal lateral margin with 6 RS, distal lateral margin with 3–4 RS, medial margin weakly convex, with 5–6 RS. Exopod extending to end of endopod, 3.6 times as long as greatest width, apically not bifid; lateral margin weakly convex, with 9–10 RS; medial margin sinuate, proximally concave, with 4 RS.

Male

Not known.

Size

Females measure 34 and 36 mm.

Variation

The appearance of the uropods is consistent, as is the arrangement of RS on the merus of P1–3. The variation shown between the two specimens is no greater than that between the two sides of the same specimens. However , in the larger specimen from Japan the RS on the merus of P1 are far smaller than in the holotype .

Remarks

This species can be readily recognized by the markedly flattened (rather than weakly vaulted) dorsal surface to pereonite 1 and the head. This is difficult to illustrate but is obvious when observing a specimen. Other distinguishing characters are: the frontal lamina is elongate in comparison to other species of the group, pereopods 1–3 are distinctive in the swollen appearance of the merus and carpus and both the propodus and dactylus are relatively short. The uropod rami are slender in comparison to many other species and the uropodal endopod lateral margin has a deep notch, the robust setae on either side being stout; the uropodal exopod extends beyond the apex of the endopod.

The holotype is in a fair condition, with many damaged appendages. One uropod is fully broken, both are rubbed. The pleotelson is, as illustrated by Richardson (1910), malformed and has a broken apex. Pereonite 1 is cracked, and the posterior legs are mostly broken off at the basis or ischium. Additional descriptive detail has been taken from the Japanese specimen, now also somewhat fragile.

Two species of the of A. deshaysiana group are known from Japanese waters: the present species and A. japonica sp. nov. There are a number of records of A. antillensis from Japan (e.g. Thielemann, 1910; Shiino, 1965; Nunomura, 1981), but without access to all reported Japanese specimens, the identity of these records remains in doubt.

Aega excisa is readily distinguished from A. japonica sp. nov. by the flat dorsal surface of the head and pereonite 1, by the elongate frontal lamina (short, anteriorly rectangular in A. japonica ) the arrangement of robust setae on the merus of pereopods 1–3 and by its smaller size ( A. japonica is between 5 and 6 cm).

Prey

No records.

Distribution

North-western Pacific , Philippines and Japan, at depths of 16 and 340 m.

Etymology

The epithet refers, presumably, to the ‘excised’ uropodal endopod.

Figures

Figure 9. Aega excisa Richardson, 1910. A–F, holotype, G–I, ♀ (ZMUC CRU3878). A, dorsal view. B, lateral view. C, frons. D, head, dorsal view. E, pereopod 1. F, pereopod 2. G, antennule. H, antenna peduncle articles 1–3, ventral view. I, antenna peduncle.

Figure 10. Aega excisa Richardson, 1910. ♀ (ZMUC CRU3878). A, mandible. B, mandible palp article 3 detail. C, maxillule. D, maxillule apex. E, maxilla. F, maxilla apex, detail. G, maxilliped palp article 5. H, maxilliped. I, maxilliped palp articles 2–5.

Figure 11. Aega excisa Richardson, 1910. ♀ (ZMUC CRU3878). A–C, pereopods 1, 2, and 7, respectively. D, uropod exopod, ventral view. E, uropod. F–G, pleopods 1–3, respectively.

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).