Aora Kroyer, 1845

Appadoo, C & Myers, A. A., 2004, Corophiidea (Crustacea: Amphipoda) from Mauritius, Records of the Australian Museum 56 (3), pp. 331-362 : 348-350

Genus Aora Kroyer

For a diagnosis see Myers, 1988a. patches of brown pigment on dorsum of head, pereon segments 2 to 7 and smaller patches of pigment on coxae 3–5 and pleonites 1–3. The dorsal surface of urosomite 1 bears a pair of slender setae. Sternal plate 1 has a transverse fold and sternal plate 2 has a well-developed forward facing process. Head anteroventral margin strongly produced; eyes subovate, with well-developed ring of ommatidia surrounding a dark core. Mandible palp articles in the ratios 7:11:20; article 2 distal end weakly expanded, with setae on inner margin; article 3 posterior margin straight, and setiferous, marginal setae of two distinct lengths. Labium outer plate distal margin with 8 to 12 robust setae. Maxilla 1 palp article 2 with 8 distal robust setae. Antenna 1 peduncle article 1 with a few robust setae on ventral margin; article 1 subequal to 2; article 3, 0.3× article 1; accessory flagellum 6- articulate, terminal article rudimentary; primary flagellum weakly setiferous and with 23-articles, aesthetacs present on articles 18 to 22. Antenna 2 robust and elongate, flagellum 11-articulate with small groups of setae. Male gnathopod 1 coxa strongly produced anterodistally, posteroproximal margin rounded; basis slender, anterior and posterior margin weakly convex; merus slender, 4× as long as broad and tapering distally; carpus elongate, 2.5× as long as broad, ventral margin with strong groups of setae; propodus subequal to length of carpus, anterior margin with groups of setae, posterior margin with strong groups of setae about two-third its length, palm slightly convex close to base of dactylus followed by a deep subquadrate excavation, with a defining tooth with round tip, palmar margin with dense groups of setae; dactylus elongate, greatly overlapping the short palm, inner margin with teeth small or obsolete. Gnathopod 2 coxa subquadrate, distal margin convex; basis slender nearly 4× as long as broad, anterior and posterior margins with short setae at regular intervals, posteroproximal margin with a few long setae; carpus elongate, over 3× as long as broad, posterior margin with dense short setae, anterior margin with a few setae; propodus slender, 2.5× as long as broad and slightly shorter than carpus, propodus anterior and posterior margin with groups of setae; dactylus fitting palm, inner margin with teeth. Pereopods 3–4 coxa subquadrate basis anterior margin and posterior margins with short setae, posteroproximal margin with a long slender setae; dactylus 0.4× propodus. Pereopods 5–7 missing. Pereopods 5 and 6 are described from smaller male of 5.2 mm: Pereopod 5 basis 1.6 times as long as broad, anterior margin with robust setae, anterodistal end with a group of slender setae, posterior margin with short setae, posterodistal end sinuous with one deep and one shallow excavation; merus distal end expanded and produced into rounded lobes; propodus slender, distal end with robust setae, dactylus 0.25× length of propodus. Pereopod 6 basis subquadrate, anterior margin with robust setae, posterior margin with short setae; propodus 1.8× carpus; dactylus 0.4× propodus. Epimera 1–3 posterodistal margins notched, with a short seta at notch. Uropod 1 peduncle and rami with robust setae. Uropod 1 interramal process 0.4× length of with well-developed terminal setae. Telson fleshy, entire, with 5 long slender setae on each side and a short seta on posterodistal margin.

Female, 6.2 mm, ovigerous. Antenna 1 slender; article 2, 1.2× article 1; article 3, 0.3× article 1; peduncular articles moderately setiferous; accessory flagellum long, 9 articulate, terminal article small; primary flagellum 24- articulate. Antenna 2 moderately setose, article 5, 1.1 times article 4; flagellum 8-articulate with a few robust setae. Gnathopod 1 coxa subquadrate, anteroventral margin rounded; basis robust, twice as long as broad; merus subquadrate, ventral margin with strong groups of setae; carpus 1.4× as long as broad; propodus 1.8× carpus, ventral margins with strong groups of setae, palmar margin straight anteriorly followed by a shallow semi-elliptical excavation and a poorly defined blunt tooth; dactylus slightly longer than palm, inner margin toothed. Female gnathopod 2 basis similar to that of male but less elongate; propodus subequal to carpus. Pereopod 5 basis anterior margin straight, anterior margin with robust setae, posterior margin with short setae. Pereopod 6 similar to that of male except merus, carpus and propodus with very long slender setae.

Variation. In younger males, one can observe the different degree of elongation of the anteroventral margin of coxa 1. In these males, the carpus of the gnathopod 1 is not very long and the propodus is about 1.4× the length of carpus (e.g., in male of 5.2 mm). The excavation in the palmar margins of gnathopod 1 is shallower, the dactylus only slightly overlaps the palm and the inner margin is strongly toothed. The posterior margin of the basis of pereopod 5 shows intermediate stages of excavation.

Distribution. Mauritius.

Habitat. Aora inermis was collected at depths of less than 1 m from a sheltered site on the north coast and a waveexposed site on the east coast of the island. This species lived mostly among Sargassum sp.

Remarks. Aora inermis n.sp. superficially resembles Aora gracilis ( Bate, 1857) as figured and described by Myers (1982: 113, fig. 74), in having an excavation on the posterodistal margin of one of the pereopods of the male. However, in the present species, the excavation is on pereopod 5 whereas in Aora gracilis it is on pereopod 6. Another striking difference between the two species is the very long merus in the male gnathopod 1 of Aora gracilis compared to the short merus in Aora inermis .

Aora inermis resembles? Aorcho curvipalma of Ledoyer (1978) described from a single male (size 5 mm) by having of A. inermis as illustrated for Aorcho curvipalma Ledoyer (1978 : fig. 22, in part). Other differences include the convex male gnathopod 2 palmar margin (palm excavate in A. curvipalma ), more robust basis in pereopod 5 and pereopod 6, the presence of a well-developed interramal process in uropod 1 (absent in A. curvipalma ), the presence of dense groups of setae on the telson in Aora inermis (few setae in Aorcho curvipalma ).

In lacking a produced, distally free merus on male gnathopod 1, this species differs from all other described species of Aora . However, it agrees with the diagnosis of Aora in all other respects and the diagnosis of Aora should be modified to accommodate this new species. Aora inermis differs from described species of Bemlos in its acute coxa 1.

Etymology. The species is named from the Latin inermis meaning unarmed as the male gnathopod 1 merus is not strongly produced.