Aega hamiota, 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 : 171-177

AEGA HAMIOTA SP. NOV. ( FIGS 22–25 , 63 )

Material examined

Holotype: ♂ (27 mm), northern New Caledonia, 18∞53.80¢S, 163∞14.10¢E, 20.ix.1985, stn 0200, MUSORSTOM IV, 535 m ( MNHN Is.5787).

Paratypes: ♀ (non-ovig. 35 mm, dissected), vicinity of Chesterfield Islands , 19∞47.90¢S, 158∞44.30¢E, 19.x.1986, stn 0363, MUSORSTOM V, 700– 685 m ( MNHN Is.5788) . ♀ (non-ovig. 31 mm), Coral Sea, east of Whitsunday Islands , Queensland, 20∞24.70¢S, 152∞57.55¢E, 22.xi.1985, 511– 508 m, Soela stn 0685/ 27/2 ( NTM Cr013498) .

Description

Body 2.3–2.6 times as long as greatest width, dorsal surfaces punctate, widest at pereonite 5, lateral margins weakly ovate. Rostral point projecting anteriorly, not ventrally folded. Eyes large, medially united, anterior clear field 9% length of head, posterior clear field 34% length of head; each eye made up of ~20 transverse rows of ommatidia, each row with ~10 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 1.1 times as long as anterior width, dorsal surface without longitudinal carina; lateral margins convex, smooth, posterior margin with elongate medial point, with 11–16 RS.

Antennule peduncle articles 1 and 2 flattened, article 2 without anterodistal lobe; articles 3 and 4 0.6 times as long as combined lengths of articles 1 and 2, article 3 2.6¥ LW; flagellum with 9 articles, extending to mid-point of eye. Antenna peduncle article 2 inferior surface with distinct longitudinal suture; article 4 2.2¥ LW, 1.3 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, 0.8¥ L article 4, 2¥ LW, inferior margin with 3 plumose setae, anterodistal angle with cluster of 3 short simple setae; flagellum with 20 articles, extending to posterior of pereonite 1.

Frontal lamina flat, longer than greatest width, oval, anterior margin rounded, without small median point, posterior margin not abutting clypeus.

Mandible molar process absent; palp article 2 with 6 distolateral setae, palp article 3 with 30 setae. Maxillule with 8 terminal RS (falcate). Maxilla medial lobe with 4 RS (3 large, 1 small); lateral lobe with 3 RS (2 recurved, 1 straight). Maxilliped endite with 1 apical setae; palp article 2 with 4 RS (3 hooked, 1 straight); article 3 with 6 recurved RS (and 1 straight); article 4 with 7 hooked RS; article 5 wholly fused to article 4, with 6 RS (straight).

Pereopod 1 basis 2.3 times as long as greatest width; ischium 0.5¥ L basis, inferior margin with 0 RS, superior distal margin with 3 RS (long acute); merus inferior margin with 5 RS, set as 3 groups (of 1, 2 and 2), superior distal angle with 7 RS (long acute); carpus 0.6¥ L merus, inferior margin with 0 RS; propodus 1.9 times as long as proximal width, inferior margin with 0 RS, propodal palm with small distal lobe, dactylus smoothly curved, 1.3¥ L propodus. P2 ischium inferior margin with 3 RS (at inferodistal angle), superior distal margin with 3 RS (long acute); merus inferior margin with 10 RS, set as single row (with separation of distal 2), superior distal margin with 5 acute RS (long acute); carpus longer than that of P1, with inferodistal lobe, inferodistal angle with 1 RS, propodus without large club-shaped distal RS. P3 similar to P2; propodus without large club-shaped distal RS. P5–7 superior margins of ischium–carpus with long, stiff, acute setae. P6 similar to P7 (but more robust, with RS more stout). P7 basis 3.3 times as long as greatest width, inferior margin with 16 palmate setae; ischium 0.5¥ L basis, inferior margin with 10 RS (7 long and 3 short), superior distal angle with 10 RS (5 stout lateral and 5 long medial), inferior distal angle with 10 RS (6 stout lateral and 4 long medial); merus L ischium, 1.9¥ LW, inferior margin with 15 RS (9 long and 6 short), superior distal angle with 15 RS (3 stout lateral and 12 long medial), inferior distal angle with 8 RS (3 stout lateral and 5 long medial); carpus 1¥ L ischium, 3¥ LW, inferior margin with 10 RS (7 long and 3 short), superior distal angle with 10 RS (3 stout lateral and 7 long medial), inferior distal angle with 11 RS (4 stout lateral and 7 long medial); propodus 0.8¥ L ischium, 3.5¥ LW, inferior margin with 6 RS (4 long and 2 short), superior distal angle with 6 slender setae (1 plumose), inferior distal angle with 4 RS.

Penes low tubercles; penial openings separated by 6% of sternal width.

Pleopod 1 exopod 2.1¥ LW, distally narrowly rounded with strongly oblique medial margin, lateral margin distally concave, medial margin strongly convex, with PMS from base; distally subtruncate, lateral margin sinuate (widest distally, proximally concave), with PMS from on distal margin only, medial margin with PMS from distal half; peduncle 1.7¥ WL, medial margin with 11 coupling hooks. Pleopod 2 appendix masculina with straight margins, 0.7¥ 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 (very weak); pleopods 2–5 peduncle distolateral margin without prominent acute RS.

Uropod peduncle ventrolateral margin with 2 RS (short), posterior lobe about 0.75¥ 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 broadly rounded. Endopod apically not bifid, lateral margin proximally and distally convex, with prominent excision positioned about two-thirds along ramus, proximal lateral margin with 6 RS, distal lateral margin with 9 RS, medial margin weakly convex, with 4 RS. Exopod extending beyond end of endopod, 1.9 times as long as greatest width, apically not bifid; lateral margin weakly convex, with 11 RS; medial margin convex, with 4 RS.

Female

Similar to males; ovigerous females not present in the material examined.

Size

Male 27 mm, females 31–35 mm.

Variation

Robust setae: only 3 specimens, so only ranges are given. There are 11–15 (6 + 5–7 + 8) RS on the pleotelson, though it is likely that some distal setae are missing, and a maximum of 16–18 seems probable. Uropod exopod medial margin with 3–6, with 5 (half) most frequent, lateral margin with 10 or 11; uropod endopod medial margin with 4 (6 once), lateral margin with 4 + 8, 4 + 9, 5 + 8 and 5 + 9.

P1–3: counts for the RS on the inferior margin of the merus: P1 with 5 as 1 + 2 + 2 with 1 + 1 + 2 + 2 once; P2 with 8 (once), 9 (3 times) and 10 (twice); and P3 with 6 (once), 9 (once), 10 (twice) and 11 (once).

As occasionally occurs in the genus, there is a substantial difference in the length-to-width ratio between some specimens. Both specimens from New Caledonia are relatively wide-bodied, c. 2.3¥ LW, with the visible portions of pereonites 6 and 7 notably short in comparison to those of the Coral Sea specimen, which is c. 2.6¥ LW. It is possible that these differences are related to maturity.

Remarks

The short uropodal endopod, widely rounded uropodal exopod, huge eyes and long acute robust setae on pereopods 5–7 ally A. hamiota to A. musorstom sp. nov., A. rickbruscai sp. nov. and A. trulla sp. nov., all from the south-western Pacific. Aega musorstom and A. rickbruscai can be immediately differentiated by lacking robust setae on the pleotelson and having far more prominent robust setae on the merus of pereopods 1–3. Additionally, A. musorstom has a prominent blade on the propodal palm of pereopods 1–3 while A. rickbruscai has a more robust propodus on pereopods 1–3. Aega trulla , while having a similar pleotelson setation, has a large propodal blade on pereopods 1–3, as well the uropodal endopod lateral margin having far fewer (6 [5 once] vs. 12–14) robust setae.

Aega hamiota sp. nov. can be identified by the large rounded uropod exopod, uropodal endopod apex not extending to the apex of the exopod, lateral margin of the uropodal endopod being densely set with robust setae (12–14 in total), slender propodus of pereopods 1–3, merus with relatively small robust setae and, uniquely within the genus, the posterior pereopods provided with long acute robust setae on superior margins of the ischium, merus and carpus (as well as the more usual inferior margins).

Prey

Not known.

Distribution

Coral Sea from New Caledonia to Queensland, Australia; one of the few species that occurs on both sides of the Coral Sea ; at depths of 508–700 m.

Etymology

The epithet is hamiota (Greek, angler; from hamus, a hook), alluding to ‘hooking into fish’; noun in apposition.

Figures

Figure 22. Aega hamiota sp. nov. A–F, holotype. G–I, ♀ paratype. A, dorsal view. B, lateral view. C, head, dorsal view. D, frons. E, pereopod 1. F, sternite 7 showing penial openings. G, antenna dorsal view. H, antenna, peduncle articles 1–3, ventral view. I, antennule.

Figure 23. Aega hamiota sp. nov. Female paratype. 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 24. Aega hamiota sp. nov. Female paratype. A–D, pereopods 2, 3, 6 and 7, respectively.

Figure 25. Aega hamiota sp. nov. A–C, holotype, remainder female paratype. A, C–E, pleopods 1–3 and 5, respectively. B, appendix masculina, dorsal view. F, uropod. G, uropod exopod, ventral view. H, uropod endopod, apex. I, uropod exopod 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).