Caribboecetes Just, 1983

Just, Jean, 1998, Siphonoecetinae (Crustacea: Amphipoda: Ischyroceridae) 7: Australian Concholestids, Ambicholestes n. gen., with a Description of Six New Species, and a New, Restricted Diagnosis for Caribboecetes Just, 1983, Records of the Australian Museum 50 (1), pp. 27-54 : 29-30

Caribboecetes Just, 1983

New restricted diagnosis. Concholestid Siphonoecetinae (sensu Just, 1988) with inner ramus of uropod 1 at most 1/2 length of outer ramus, flattened, with robust setae on margin. Uropod 3 without ramus. Mandibular palp 2- articulate, blunt, reaching to about apex of incisor. Inner lobes of lower lip simple. Ocular field of eye lobes not inflated. Article 2 of pereopod 7 without single midlateral row of setae. Oostegites on pereopods 2-5. Gills on pereopods 4-6.

Type species. Caribboecetes barbadensis Just, 1983 (original designation).

Additional species. Caribboecetes intermedius Just, 1984a , C. jenikarpae Just, 1984a , C. pterycornis Just, 1984a (tentatively).

Further description. Rostrum present or absent. Coxal plates 5-6 antero- as well as posterolobate (except C. pterycornis , posterolobate only). Upper lip with apical notch. Antenna 1 article 3 50-60% (c. pterycornis 70%) length of article 1, article 2 80-95% length of article 1. Antenna 2 article 4 75-90% length of article 5. Antenna 1 reaching from just beyond peduncle of antenna 2 to about tip of flagellum of antenna 2. Pereopod 1 article 6 80- 90% length of article 5, without posteroapical tooth, with posteroapical robust seta and 1-2 robust setae on posterior margin; article 5 with 1 posteroapical robust seat. Pereopod 2 article 6 10-45% longer than article 5 (except c.

.

pterycornis , 70%), with posteroapical triangular tooth and varying number of posterior robust setae. Pereopods 3-4 with posteriorrobust setae on article 5. Pereopods 5-6 with crescent of equal-sized short, robust setae on article 5. Pleopods with peduncle broader than long; rami as long as or longer than width of peduncle; inner ramus slightly longer than outer ramus.

Distribution. Caribbean, Pacific Mexico; from low water mark to 54 m.

Australian Concholestids

A full cladistic analysis of the Siphonoecetinae , and the concholestid component in particular, is not feasible at the present time. Many siphonoecetines remain to be described, including groups of species exhibiting characters which will influence the outcome of such an analysis. The problem is compounded by the present uncertainties, at the outgroup level, of where the Siphonoecetinae belong in the Corophioidea , and by difficulties in delimiting families with which Siphonoecetinae are believed to be related. The proposed classification of the Australian concholestids is based on immediately obvious synapomorphies, such as a complex lower lip versus a simple one, and an elongated, I-articulate, pointed mandibular palp versus the otherwise ubiquitous short, club shaped palp with a tiny second article (in a single known species the first article is broadly expanded). The use of subgeneric classification is a subjective convenience to keep together species sharing a major synapomorphy, e.g., the complex lower lip in Ambicholestes , but differing at a perceived subordinate sister group level, here Ambicholestes sensu stricto versus Ambicholestes (Austrolestes) . This use of the subgenus category is consistent with Just (1983 - Siphonoecetes , and I985- Australoecetes ).

Urosomites and the telson

In my first contribution to the taxonomy of the Siphonoecetinae ( Just, 1983) an important character in the diagnosis of the new genus Caribboecetes was urosomite 3 and telson fused dorsally". This still holds good for the four species retained in that genus. For the three species of Caribboecetes described by Just (1984a, C. crassicornis , C. magellani , and C. squamiferus ), but here transferred to Ambicholestes n.gen., it was noted (Just, I984a: 38) that the urosomite-telson configuration is not intraspecifically stable (occurrence of incomplete fusion between urosomite 3 and the telson, more or less complete fusion between urosomites 1 and 2 and/or 2 and 3). The same lability is found in the Australian concholestids and will be commented upon where relevant. For that reason the urosomite-telson configuration has not been included in the diagnoses of Caribboecetes and the new genus group taxa below.

Stridulation organs

Three species in Ambicholestes S.S., viz., A. crassicornis , A. magellani , and A. trilobatus n.sp. possess what appears to be a sound producing organ. Coxal plate 2 carries on the posteroventral margin a row of backward and slightly outward pointing teeth; pereopod 2 article 2 carries medially along the anterior margin a number of short, pointed, proximally inflated, hollow setae, (Just, I984a, figs 13-14, 16; this paper Fig. 8 ). When pereopod 2 is moved forward the setae come into contact with the coxal plate teeth. This may result in the production of sound. The different arrangement of setae in the three species ( A. crassicornis : nearly straight row, A. magellani : on two projecting lobes, A. trilobatus : on three projecting lobes) further suggests differences in the sound patterns produced. Stridulation in live animals has not been observed.

In this paper the three species are placed inAmbicholestes s.s. together with A. squamiferus , A. cygnatratus n.sp. and A. poorei n.sp. for other reasons, but their joint possession of a unique potential stridulation mechanism suggests they form a clade which may eventually warrant separate genus group recognition.

Sexual dimorphism

Some groups of siphonoecetines exhibit distinctive sexual dimorphism ( Siphonoecetes (Centraloecetes) : uropod 1, Just, 1983; Australoecetes (Stebbingoecetes) : coxal plate 1, Just, 1985; Africoecetes : pereopod 2, Just, I984b). No such differences between the sexes have been observed in species of Caribboecetes or Ambicholestes . In species of Ambicholestes , as in all other siphonoecetines, male antennae are longer, antenna 1 often with more flagellar articles, stouter, and more densely setose than in females; the body length of adult males is greater than in adult females; and females often have fewer robust setae on pereopods and uropods. The number of robust setae mentioned in descriptions below is the maximum number found in adult males, or otherwise in the material available.

Figures

Fig. 8. Ambicholestes (Ambicholestes) trilobatus n.sp., holotype. col, ventral margin of coxal plate 1 with posterior, presumed stridulation teeth; p, pereopod (1, 2, 3 and 5); us, urosome, dorsal view.