Aega deshaysiana (Milne Edwards, 1840)

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 : 136

AEGA DESHAYSIANA AND RELATED SPECIES

Initially, on examining a limited number of specimens, it seemed that there were a number of similar species, with strong Southern Hemisphere representation, all of which were related to the Atlantic species A. deshaysiana and A. antillensis . They all have large eyes, which in some species occupy almost all of the head, robust pereopods, weakly flattened antennules, an anvil-shaped frontal lamina, pereopods 1–3 often with a small to large lobe on the propodal palm, relatively long robust setae on pereopods 4–7, an elongate pleotelson with a prominently defined apex, the distal margin of which usually has a groove in which the setae are set (see Figs 1G , 29G , 49E ), uropods that characteristically have a deeply notched endopod lateral margin (described as falcate by Brusca, 1983) and the transverse plane of the exopod oblique to that of the endopod.

As more species were discriminated, notably those from the large series of excellently preserved material collected by MUSORSTOM off New Caledonia, it became increasingly apparent that none of the abovementioned characters hold up absolutely. All species have the ‘anvil-like’ frontal lamina; however, in some the notching of the uropod is scarcely present. The eyes are large and medially united in most species, but are clearly separate in A. deshaysiana and A. birubi sp. nov. for example. Most species have stout anterior pereopods, the inferior margin of the propodus often with a small distal lobe, occasionally with a large plate-like blade; all have relatively long robust setae on the posterior pereopods (in comparison to species such as A. monophthalma Johnston, 1834 , A. semicarinata Miers, 1875 or A. magnifica ( Dana, 1853) ; see descriptions below). In this paper I group A. deshaysiana and related species in order to facilitate their identification, resolve the identity of named species and describe those hitherto undescribed and provide details of what is known of their global distribution.

There are a few additional species that appear similar to those described here, most notably A. magnifica ( Dana, 1853) . Figures of pereopod 1 and of the uropods suggested similarities to the group, despite the relatively small size of the eyes. Examination of material close to the type location showed that it is similar to those Aega which have peduncular articles 1 and 2 of the antennule large and anteriorly expanded. A. magnifica , in common with species such as A. monophthalma , A. semicarinata , and A. urotoma Barnard, 1914 , has the uropodal rami extending posterior to the pleotelson apex, a dense mass of setae along the margins of the pleotelson of the uropods and coplanar uropodal rami. In addition, in all these species the anterior (or inferior, depending on perspective) margin of the antennule peduncle article is strongly defined, with a blade-like edge. Two other species are similar to A. magnifica : A. acuminata Hansen, 1897 , from the Galapagos and off Costa Rica and A. maxima Hansen, 1897 , from off Cocos Island ( Costa Rica) between Panama and the Galapagos. A. magnifica is described below.

The phylogenetic significance of these character states and the monophyly of the group are not assessed. Given this caveat, this group is found worldwide and there are numerous species. This paper describes 15 species, 12 of them new, and provides notes for a further six for which material was inadequate for descriptive purposes.

Figures

Figure 1. Aega antillensis Schioedte & Meinert, 1879. A–D, holotype, ZMB 4046, remainder male 18.5 mm, Gulf of Mexico, FSBC I 18381. A, dorsal view. B, lateral view. C, head. D, frons. E, antennule. F, antenna. G, pleotelson apex, ventral view. H, penial openings.

Figure 29. Aega kixalles sp. nov. A–D, H, holotype, remainder female paratype, 38 mm. A, dorsal view. B, lateral view. C, head, dorsal view. D, frons. E, antennule. F, antenna peduncle. G, pleotelson posterior margin.

Figure 49. Aega umpara sp. nov. A–F, J, holotype, remainder paratype AM P37511. A, dorsal view. B, lateral view. C, head, dorsal view. D, frons. E, pleotelson posterior margin, dorsal view. F, sternite 7 showing penial openings. G, antennule. H, antenna peduncle. I, antenna peduncle, articles 1–3. J, pereopod 1, distal articles.