Aora karibu, Vader & Krapp, 2005

Vader, Wim & Krapp, Traudl, 2005, Crab-associated amphipods from the Falkland Islands (Crustacea, Peracarida), Journal of Natural History 39 (33), pp. 3075-3099 : 3086-3091

Aora karibu n. sp.

( Figures 7 –9)

Type material

Holotype: one male 5.8 mm, together with Gammaropsis , East Falkland, Choiseul Sound, 30 m, from Eurypodius latreillei , caught in baited traps, 29 October 2003, A. and W. Vader leg. Deposited at TromsØ Museum as a slide 13845.

Type locality

Choiseul Sound, Falkland, from Eurypodius .

Diagnosis

A rather nondescript Aora with a not very setose second gnathopod, with merus long, acute and unadorned. Interramal spine on second uropod virtually absent.

Description

Male 5.8 mm. Body: dorsally smooth. Head with lateral lobe broadly rounded, eyes large, roundish, dark, largely on cephalic lobes. Epimeral plates 2–3 with small posterodistal tooth, Ep3 with posterior margin convex.

Figure 9. Aora karibu n. sp.: P5peraeopod 3, 4, 5, 6 (×10); Ep5epimeral plate 2, 3 (×6); U5uropod 1, U2 right and left (×10); T5telson + U3 (×20); U3 rami distally, enlarged (×63).

Antennae: A1.A2, about as long as body; peduncle article 1 broader than articles 2 and 3, article 2.1.3; peduncle article 1 with a row of strong setae ventrally, article 2 with small groups of short setae both dorsally and ventrally, article 3 with distal setae only. Flagellum with 21 elongate articles, slender. Accessory flagellum thin, five-articulate. A2 with peduncle less slender than A1, articles 4 and 5 subequal, sparsely setose, flagellum shorter than article 5 of peduncle, nine-articulate.

Mouthparts typical for the genus (cf. e.g. Myers 1973). Mandible palp slender, length ratio articles 1:2:3 is 10:17:21. Maxilla 1 palp article 2 with eight robust setae. Maxilliped: palp carpus with acute falcate prolongation on the upper side, of about half length of propodus.

Gnathopods: Gn1.Gn2, with coxa moderately produced anteroventrally, basis with margins weakly convex, merus of typical Aora -form, the acute tip reaching just beyond the carpus, carpus and propodus broad, subequal in length, propodus with palm slightly oblique, palmar corner defined by acute, triangular, serrate ‘‘tooth’’, and strong robust seta, palm concave, with two further rounded ‘‘teeth’’ on proximal third; dactylus strong, falcate, much longer than palm. Gn2 with coxa sub-quadrate, with rounded corners, basis with posterior margin strongly convex, with a few long setae, carpus and propodus subequal in length, with many setae along posterior margin, propodus also medially setose. Palm oblique, slightly convex, demarcated by one strong and a few minor robust setae, dactyl falcate, as long as palm.

Peraeopods: P3–4 similar, coxae subquadrate, basis slender, with short setae on both margins and a few longer setae on posterior margin; propodus narrow, dactylus slender, ca 60% propodus. P5 shorter than P3–4, with basis broadened, and propodus longer than carpus; dactylus short, falcate. P6 long, slender; basis broadened, anterior margin crenulate, both margins with short marginal setae; length ratio merus: carpus: propodus is 40: 25: 50, dactylus ca 30% length of propodus, straight, slender, acute.

Uropods: U1 with peduncle slightly longer than rami, both with marginal robust setae; interramal spine strong,.40% length of ramus, rami subequal. There is a pore, possibly the exit of a gland, near the basis of the peduncle (see Figure 8 , with detail, and Figure 9). U2 with peduncle shorter than rami, interramal spine absent, outer ramus slightly shorter than inner. U3 with peduncle broad, clearly shorter than rami; one robust seta on each distal corner; rami with rounded tips, and long distal robust setae, as well as marginal ones; outer ramus with nail-like distal end which could be interpreted as a minute second article.

Telson fleshy, three-dimensional, with acute blade-like crests on either side leaving a Vshaped dorsal depression; on the inner margin with a number of long setae. When squashed the telson appears 25% ‘‘cleft’’, which, however, is not the case.

Gills on P2–7.

Etymology

Karibu, here used as a noun in apposition, signifies ‘‘welcome’’ in Swahili. Most appropriately, it is also the name of the most welcoming home of the Myers family in Fountaintown, Ireland, and the name is given in grateful appreciation of both the great hospitality that both authors have received there, and of the scientific help given us by Alan Myers, the world authority on the family Aoridae .

Discussion

Myers and Moore (1983) presented a key to the 14 Aora species (males only) then known. Since then two more species have been described, i.e. A. pseudotypica Hirayama, 1984 and A. inermis Appadoo and Myers, 2004 . With the combination of characters of a not very setose Gn2, and the absence of special processes on basis and/or carpus of Gn1, the present species keys out to A. kergueleni Stebbing, 1888 from Kerguelen. It differs, however, from A. kergueleni in many characters, such as a longer and more slender merus, and a broader carpus and propodus on Gn1, and the virtual absence of an interramal spine of U2. In the form of the gnathopods A. karibu is somewhat more similar to A. maculata (Thomson, 1879) from Australia and New Zealand, but that species has heavily setose antennae.

Of the more recently described species, A. pseudotypica from Japan has a very different Gn1, with a very elongate carpus and propodus, without a clear palm, and a very long dactylus. In A. inermis from Mauritius the merus of Gn1 is uncommonly short, and the palm of the propodus much more oblique.

This is the first time that an Aora species has been found as a possible associate of majid crabs, although this single specimen of course does not prove the association. Earlier, an as yet unidentified Aora has been found on hermit crabs off New South Wales, Australia (W. Vader, unpublished data), while A. hebes Myers and Moore, 1983 seems to be an associate of sponges.

Figures

Figure 7. Aora karibu n. sp.: male habitus 5.8 mm; A5antenna 1, 2; head with lateral lobe (×10); all mouthparts (×20): Md5mandible from both sides; Mx5maxilla 1, 2; UL5upper lip; LL5lower lip.

Figure 8. Aora karibu n. sp.: Gn5gnathopod 1 (×10), enlargement (×20); Gn2 (×10), enlargement (×20); Mxp5maxilliped (×20), palp and inner plate in enlargement (×40); U5uropod 3 (×10), enlargement of proximal part of peduncle (×40).