Aega japonica, 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 : 177-181

AEGA JAPONICA SP. NOV. ( FIGS 26–28 , 62 )

Aega antillensis –? Thielemann, 1910: 26, plate, figs 1, 2; Nunomura, 1981: 49 (?part).

Aega deshaysiana – Nierstrasz, 1931: 182 (part); Brusca, 1983: 13 (part, Japanese specimen).

Material examined

Holotype: ♀ (non-ovig. 38 mm), Hokadate Bay , Hokkaido, Japan, 18.ii. 1992, 120 m, coll T. Komai ( USNM 1014733 ).

Paratypes: ♀ (non-ovig. 54 mm), Wakayama, southern Honshu , Japan, no other data ( TSM Cr13017; loaned by Noburu Nunomura) . ♀ (non-ovig. 38 mm), Japan, coll. Rev. H. Loomis, previously dissected (R.C. Brusca labels) ( USNM 22687 ) .

Description

Body 3.0 times as long as greatest width, dorsal surfaces smooth (very weakly punctate), widest at pereonite 5, lateral margins subparallel. Rostral point projecting anteriorly, not ventrally folded. Eyes large, medially united, anterior clear field 18% length of head, posterior clear field 46% length of head; each eye made up of ~23 transverse rows of ommatidia, each row with ~9 ommatidia; eye colour dark brown. 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 free, not overlapped by lateral margins of pleonite 4, or 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 (indistinct), with 6 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 2.5¥ LW; flagellum with 9 articles, extending to mid-point of eye. Antenna peduncle article 2 inferior surface without distinct longitudinal suture; article 4 1.9¥ LW, 1.5 times as long as combined lengths of articles 1–3, without deep longitudinal groove (with longitudinal depression), inferior margin with 1 plumose setae (setae missing), and 0 short simple setae; article 5 not markedly wider or flatter than article 4, 0.9¥ L article 4, 2.3¥ LW, inferior margin with 2 plumose setae, anterodistal angle with cluster of 3 short simple setae; flagellum with 16 articles, extending to posterior of pereonite 1.

Frontal lamina flat, longer than greatest width, rectangular, anterior margin anteriorly truncate, without small median point, posterior margin not abutting clypeus.

Mandible molar process absent; palp article 2 with 6 distolateral setae, palp article 3 with 31 setae. Maxillule with 7 terminal RS (falcate). Maxilla medial lobe with 4 RS (1 hooked, 2 straight, weakly biserrate); lateral lobe with 4 RS (large, hooked). Maxilliped endite with 2 apical setae; palp article 2 with 5 RS (1 hooked, 3 slender curved); article 3 with 7 recurved RS (1 minute); article 4 with 6 hooked RS; article 5 partly fused to article 4, with 8 RS (straight).

Pereopod 1 basis 2.2 times as long as greatest width; ischium 0.5¥ L basis, inferior margin with 0 RS, superior distal margin with 1 RS; merus inferior margin with 5 RS, set as single row (of 3 and 2), superior distal angle with 2 RS; carpus 0.5¥ L merus, inferior margin with 0 RS; propodus 1.2 times as long as proximal width, inferior margin with 0 RS, propodal palm with small distal lobe, dactylus smoothly curved (robust), 1.4 L propodus. P2 ischium inferior margin with 1 RS, superior distal margin with 1 RS; merus inferior margin with 7 RS, set as single row, superior distal margin with 2 acute RS; carpus similar in size to that of P1, inferodistal angle with 1 RS (minute), propodus without large club-shaped distal RS. P3 similar to P2; propodus without large club-shaped distal RS. P6 similar to P7. P7 basis 3.3 times as long as greatest width; ischium 0.5¥ L basis, inferior margin with 5 RS (set as 1, 1, 2 and 1), superior distal angle with 3 RS, inferior distal angle with 6 RS; merus 0.8¥ L ischium, 2.2¥ LW, inferior margin with 5 RS (set as 2 and 3), superior distal angle with 6 RS, inferior distal angle with 4 RS; carpus 0.9¥ L ischium, 2.7¥ LW, inferior margin with 3 RS (set as 1 and 2), superior distal angle with 4 RS, inferior distal angle with 7 RS; propodus 0.7¥ L ischium, 4.5¥ LW, inferior margin with 2 RS (single cluster), superior distal angle with 2 slender setae, inferior distal angle with 4 RS.

Pleopod 1 exopod 1.9¥ LW, distally narrowly rounded, medial margin weakly oblique, lateral margin weakly convex, medial margin strongly convex, with PMS from base; endopod 2¥ LW, distally subtruncate, lateral margin sinuate (widest subdistally, proximally concave), with PMS from distal half, medial margin with PMS from distal one-third; peduncle 1.5¥ WL, medial margin with 10 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, 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 two-thirds along ramus, proximal lateral margin with 4 RS, distal lateral margin with 4 RS, medial margin straight, with 5 RS. Exopod extending to end of endopod, 3 times as long as greatest width; lateral margin weakly convex, with 10 RS; medial margin sinuate, proximally concave, with 4 RS.

Size

Females 38–54 mm, males not known.

Variation

Robust setae: only 3 specimens, so only ranges are given. Pleotelson with 6–8 (3 + 3–4 + 4) RS, though it is likely that some distal setae are missing. Uropod exopod medial margin with 3–5, with 4 (half) most frequent, lateral margin with 10–12; uropod endopod medial margin with 4 or 5, lateral margin with 3 + 4, 3 + 5, 4 + 4 (half) and 4 + 5.

P1–3: counts for the RS on the inferior margin of the merus: P1 with 5 as 3 + 2, P2 with 7 (all), and P3 with 7 (all).

Remarks

The semirectangular shape of the frontal lamina, setation pattern on the inferior margin of pereopods 1–3, together with the weak propodal lobe and ill-defined pleotelson apex are characters by which the species can be identified. The merus of pereopod 1 has five large robust setae. Of those species that have medially united eyes and a small propodal lobe on pereopods 1– 3, all have fewer robust setae which are set in distinctly separate clusters (e.g. A. kwazulu sp. nov., A. umpara sp. nov. and A. warna sp. nov.) or have wider uropodal exopod with long setae on the posterior pereopods (e.g. A. rickbruscai sp. nov.).

Two species of the A. deshaysiana group are recorded from Japan and the North Pacific: this one and A. excisa . The identities of the records earlier than Brusca (1983) remain uncertain. Thielemann’s (1910) material is not available (presumed destroyed during World War II), and I have not seen Nunomura’s (1981) material, indicated to be one male and five females up to 5 cm in length.

Prey

Not known.

Distribution

Off Pacific coasts of Japan, from southern Hokkaido to southern Honshu; 120 m is the only depth record.

Etymology

The epithet is adapted from Japan, the country of origin for the material described here; noun in apposition.

Figures

Figure 26. Aega japonica sp. nov. A–D holotype, remainder paratype, Wakayama. A, dorsal view. B, lateral view. C, head, dorsal view. D, frons. E, antennule. F, antenna peduncle. G, antenna, peduncle articles 1–3, ventral view.

Figure 27. Aega japonica sp. nov. A–D, G, H, holotype. E, F, paratype, Wakayama. A, mandible. B, mandible palp article 3 detail. C, maxilla, detail. D, maxillule apex. E, maxilliped. F, maxilliped palp article 5. G, maxilliped palp articles 2–5.

Figure 28. Aega japonica sp. nov. A–C, pereopods 1, 3 and 7, respectively. D, pereopod 1, mesial aspect, ischium superior distal angle. E, pleopod 1. F, pleopod 2. G, 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).