Cristimenes, Ďuris, Zdenek & Horka, Ivona, 2017

Ďuris, Zdenek & Horka, Ivona, 2017, Towards a revision of the genus Periclimenes: resurrection of Ancylocaris Schenkel, 1902, and designation of three new genera (Crustacea, Decapoda, Palaemonidae), ZooKeys 646, pp. 25-44 : 30-33

Cristimenes gen. n.

Type species.

Periclimenes (Cristiger) commensalis Borradaile, 1915, by present designation.

Included species.

Cristimenes commensalis (Borradaile, 1915), comb. n. (Figs 2A, B, 3F); Cristimenes cristimanus (Bruce, 1965), comb. n. (Figs 2C, D, 3E); and Cristimenes zanzibaricus (Bruce, 1967), comb. n.

Diagnosis.

Carapace smooth; rostrum well developed, subequal to antennular peduncle, compressed, usually with 5-7 low dorsal and 0-3 ventral teeth, lateral carinae with depressed supraorbital tooth, orbit feebly developed, epigastric tooth absent, inferior angle distinct, hepatic tooth close to antennal tooth and slightly lower positioned. Pleon smooth, fourth and fifth pleura posteroventrally angulate. Telson with two pairs of small dorsal spines on posterior half, and with three pairs of posterior spines. Eyes with globular cornea. Basal antennular segment with 2-3 acute distolateral teeth. Antenna with basicerite unarmed, scaphocerite moderately broad, with distolateral tooth small, not reaching distal level of lamina. Epistome with pair of lateral rounded tubercles. Mandible without palp, molar process robust, incisor process normal, with 3-4 terminal teeth; maxillula with bilobed palp, laciniae moderately broad; maxilla with simple palp, basal endite slender, feebly bilobed or simple, coxal endite obsolete, scaphognathite moderately broad; first maxilliped with simple palp, basal and coxal endites fused, exopod with distinct caridean lobe, flagellum slender with 4 plumose distal setae, epipod bilobed; second maxilliped with normal endopod, propodus feebly produced medially, exopod similar to flagellum of first maxilliped, coxa with elongate epipod without podobranch, arthrobranch rudimentary; third maxilliped with slender endopod, ischiomerus distinct from basis, exopod as in second maxilliped, coxa with large subcircular lateral plate, arthrobranch rudimentary. Fourth thoracic sternite without median process. First pereiopods slender, chela with fingers tapering distally and feebly or distinctly subspatulate with entire cutting edges, coxa with obsolete distoventral lobe. Second pereiopods similar and subequal; cutting edges of fingers dentate or denticulate; palm elongate, subequal or longer than fingers, subterminally articulated to short cup-shaped carpus, with pair of proximal lobes fitting dorsally to carpal cavity; carpus and merus unarmed. Ambulatory pereiopods slender, dactyli bi- or triunguiculate (i.e. with or without dorsal spinule behind unguis), unguis long, almost subequal to corpus length; propodus with ventral spinules and tufts of soft setae. Uropodal exopod elongate, laterally straight, with small distolateral tooth with mobile spine medially.

Etymology.

A combination of the subgeneric name Cristiger (see below) proposed by Borradaile, 1915 and Periclimenes in which genus the species were previously placed; gender masculine. As suggested by Holthuis (1993), the etymology of the name Cristiger (Latin = crest-bearer) was possibly in reference to the convex upper margin of the rostrum in the type species (from crista = crest, and gero = to bear).

Figures

(selected). Holthuis (1952: figs 18-19), Miyake and Fujino (1968: fig. 2 e–g), Bruce (1965: figs 1-2; 1967: figs 26-29; 1982: fig. 2).

Systematic position.

The present new genus is closely related to three crinoid-associated genera, Araiopontonia Fujino & Miyake, 1970, Laomenes AH Clark, 1919, and Unguicaris Marin & Chan, 2006. This was already suggested by Marin and Chan (2006), and later supported by phylogenetic analyses ( Kou et al. 2013, Gan et al. 2015, Horká et al. 2016). All these echinoderm-associated shrimps have a well-developed, somewhat downturned rostrum, generally dentate both dorsally and ventrally; the epistome is with a pair of lateral lobes (low, rounded in Cristimenes gen. n. and Araiopontonia , but acutely produced in the remaining genera); similar and subequal second pereiopods, and ambulatory legs possessing a specific type of ‘triunguiculate’ dactylus with a long main unguis. Such dactyli are secondarily reduced to a more biunguiculate state by the reduction of the dorsal spinule in the echinoid-associated species Cristimenes cristimanus and Cristimenes zanzibaricus , as well as in the crinoid associated genus Laomenes . The depressed supraorbital teeth associated with the lateral rostral carina are a synapomorphic character for the group, however, secondarily lost in Unguicaris . Such a reduction of the supraorbital teeth and lateral carinae was illustrated in some specimens of Cristimenes commensalis by Monod (1976), or Bruce (1982).

Cristimenes gen. n., together with Araiopontonia , can be distinguished from the genera Laomenes and Unguicaris by the rounded lateral lobes on the epistome (vs. acute projecting lobes). The new genus differs from all the three genera by a 3-dentate mandibular incisor (vs. distally expanded, multidentate), and by the unique carpo-propodal articulation of the second pereiopods, with the subterminal proximo-ventral articulation on the propodus leaving a distinctive posterior part of the propodus dorsally overhanging the articulation (Fig. 2). This lobe is deeply subdivided by a short but deep longitudinal groove into a pair of lobes which smoothly fit into the dorsal cavity of the short cup-shaped carpus when the propodus is extended anteriad. The proximal end of the propodus is then well hidden inside the carpus from dorsal view.

Range.

Widely distributed throughout the whole Indo-West Pacific region.

Ecology.

The genus Cristimenes comprises a single crinoid-associated species, Cristimenes commensalis comb. n., with the other two species, Cristimenes cristimanus comb. n., and Cristimenes zanzibaricus comb. n., living on echinoids ( Echinodermata: Crinoidea, Echinoidea).

Remarks.

The genus Cristimenes is established here for three species, with Periclimenes (Cristiger) commensalis as the type species. This species was designated as the type species of the subgenus Cristiger Borradaile, 1915 by Holthuis (1955) since the previous designation of Alpheus scriptus Risso, 1822 by Borradaile (1917) as the type was invalid. As pointed out by Holthuis (1955, 1993), the name Cristiger Borradaile is a junior homonym of Cristiger Gistel, 1848 ( Hymenoptera ), and thus not available to be used for the present genus.

Key to species identification of Cristimenes gen. n.