Ancylomenes, Okuno & Bruce, 2010

Okuno, J. & Bruce, A. J., 2010, Designation of Ancylomenes gen. nov., for the ‘ Periclimenes aesopius species group’ (Crustacea: Decapoda: Palaemonidae), with the description of a new species and a checklist of congeneric species *, Zootaxa 2372 (1), pp. 85-105 : 86-87

Ancylomenes gen. nov.

Diagnosis. Medium sized pontoniine shrimp with subcylindrical body, with relatively small cephalothorax and large abdomen. Rostrum well developed, usually arched, dorsal margin dentate, ventral margin dentate or edentate, lateral and ventral carinae obsolete. Carapace smooth, glabrous, antennal and hepatic spines present, supraorbital spine or eave absent, epigastric spine present or absent, inferior orbital margin strongly produced, with reflected inner ventral flange, pterygostomial angle blunt, unarmed. Abdomen smooth, tergum of third somite distinctly posteriorly produced, pleura of fourth and fifth somites posteriorly produced. Telson with 2 pairs of dorsal spines, 3 pairs of posterior spines. Ophthalmic somite with well developed or obsolete interocular process. Second and third thoracic sternites not considerably elongate, fourth sternite without finger-like median process. Antennule well developed, upper flagellum biramous. Antenna with basicerite with proximal angular process dorsally, scaphocerite well developed. Epistome unarmed. Mandible without palp, molar process slender, incisor process well developed, dentate. Maxillula with feebly bilobed palp, laciniae slender. Maxilla with slender, tapering palp, distal endite well developed, simple or bilobed, proximal endite obsolete, scaphognathite narrow. Maxillipeds with functional exopods. First pereiopods with fingers simple, not spatulate, cutting borders entire, not denticulate. Second pereiopods elongate, similar or dissimilar, fingers with cutting borders dentate or edentate, merus without distoventral spine. Ambulatory pereiopods slender, propodi spinulate ventrally, dactyli simple or biunguiculate. Endopod of male first pleopod oval, with small appendix interna.

Type species. Periclimenes venustus Bruce, 1990 , by present designation.

Etymology. From Greek word ancylos meaning bent, and part of the generic name Periclimenes , in allusion to the well developed and humpbacked third abdominal tergum of the members of the genus. Gender: masculine.

Distribution. Tropical to warm-temperate waters of the Indo-West Pacific, Eastern Pacific, and Western Atlantic Ocean.

Ecology. Species of Ancylomenes gen. nov. are associated with cnidarian marine invertebrates. Most of species are also known to clean fishes (e. g. Limbaugh et al 1961; Nizinski 1989; Okuno & Nomura 2002; Becker & Grutter 2004).

Systematic position. Closely related to Periclimenes sensu stricto, in which the species were formerly included. Distinguished from that genus by the small cephalothorax and larger abdomen, nearly always acutely produced inferior orbital angle with reflected inner flange, large anterolateral lobe on proximal segment of antennular peduncle, dorsoproximal angular process of antennal basicerite, and well developed or obsolete interocular process of ophthalmic somite.

Ancylomenes gen. nov. is also similar to Leptomenaeus Bruce, 2007 in sharing several morphological features. These two genera are discriminated on account of the structure of second and third thoracic sternites, antennular peduncle, and second pereiopod pointed out by Ď uriš & Horká (2008).

Remarks. Periclimenes lucasi from the tropical Eastern Pacific, and P. pedersoni and P. anthophilus from the western Atlantic Ocean have been reported several times, but the structure of their inferior orbital margin, ophthalmic somite and antennal basicerite have not previously been described in detail. We examined additional specimens of these three species, and found that they possess the diagnostic features of Ancylomenes gen. nov. as mentioned above. These species are also associated with sea anemones, as well as being reef fish cleaners. This behaviour is also similar to that of some of the Indo-Pacific species. Thus, we regard without doubt that P. lucasi , P. pedersoni and P. anthophilus also belong to Ancylomenes gen. nov.

Bruce (2008a) and Okuno & Imazeki (2008) regarded Periclimenes tonga Bruce, 1990 , known only by the ovigerous female holotype, as a member of ‘ P. aesopius species group’. However, the unarmed basicerite of the antenna and the finely tuberculate second pereiopod distinguish P. tonga from the members of Ancylomenes gen. nov. (see Bruce 1990a). Thus, we consider P. tonga as not assigned to the present new genus.

In conclusion, fifteen Indo-Pacific, one Eastern Pacific, and two Western Atlantic species are now placed the new genus. The key to the species of Ancylomenes gen. nov. is provided below.