Actinimenes, 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 : 28-30

Actinimenes gen. n.

Type species.

Periclimenes ornatus Bruce, 1969, by present designation.

Included species.

Actinimenes inornatus (Kemp, 1922), comb. n. (Fig. 3C); Actinimenes ornatus (Bruce, 1969), comb. n. (Fig. 3D); and Actinimenes ornatellus (Bruce, 1979), comb. n.

Diagnosis.

Carapace smooth; rostrum well developed, compressed, dorsal and ventral margins convex, with 7-10 dorsal teeth (posterior tooth behind orbits) and 0-2 ventral teeth, lateral carinae and orbit feebly developed, epigastric and supraorbital spines absent, inferior orbital angle usually produced, rounded, antennal tooth marginal, hepatic tooth close to level of latter. Pleon smooth, third segment not posteriorly produced, pleura rounded. Telson with two pairs of moderately large dorsal marginal spines situated on anterior and posterior thirds of telson length; three pairs of posterior spines, lateral spines smaller than dorsal spines. Eyes with globular cornea, small additional pigment spot dorsally on corneal margin. Antennule well developed. Antennal basicerite armed with lateral tooth; scaphocerite well developed, moderately broad, with distolateral tooth small, not reaching distal end of lamella. Mandible without palp, molar process robust, incisor process as usual for the family. Maxillula with bilobed palp, laciniae as usual for the family. Maxilla with simple palp, basal endite slender, deeply bilobed, coxal endite obsolete, scaphognathite moderately broad. First maxilliped with simple palp, basal endite fused with coxal endite, exopod with large caridean lobe, flagellum slender with several plumose distal setae, epipod feebly bilobed. Second maxilliped with normal endopod, propodus not produced distomesially, exopod similar to first maxilliped, without accessory lobe, coxa with oval epipod without podobranch. Third maxilliped with slender endopod, ischiomerus fused to basis, exopod as in second maxilliped, coxa with oval lateral plate, arthrobranch rudimentary or lacking. Fourth thoracic sternite with broad transverse ridge subdivided by median incision. First pereiopods moderately slender, chela with fingers subequal to palm, deeply subspatulate with entire cutting edges, coxa with setose distoventral lobe. Second pereiopods well developed, smooth, similar and equal, fingers with several small recurved teeth on proximal half, palm subcylindrical, longer than fingers, carpo-propodal articulation terminal, carpus much shorter than palm, merus unarmed, coxa without distoventral lobe. Ambulatory pereiopods moderately slender, propodus without ventral spines, dactyli with stout unarmed corpus, unguis elongate, curved. Endopod of male first pleopod simple, elliptic, feebly spinulose medioproximally, with several setulose setae distolaterally. Male second pleopod with appendix masculina slender, with several simple terminal and lateral setae. Uropods normal, exopod with small distolateral tooth and normal movable spine.

Etymology.

From Actiniaria , the order of Anthozoa which comprises the host sea anemones for the genus, and Periclimenes to which genus the species previously belonged; gender masculine.

Figures

(selected). Kemp (1922: figs 43-46), Bruce (1976: 10-11; 1979: figs 3B, 4-7, Pl. 1: fig. B–E; 1982: figs 11-12), Fransen (1989: figs 2-3).

Systematic position.

Based on recent molecular studies ( Gan et al. 2015, Horká et al. 2016), species of the genus Actinimenes gen. n. show a close phylogenetic relationship to two groups of taxa, Zenopontonia Bruce, 1975 and some other echinoderm-associated taxa on the one hand, and to the Periclimenes diversipes species group on the other hand. While the latter are also cnidarian associates, they are distinctly smaller species with more slender ambulatory pereiopods and dactyls, but mainly with very distinctive second pereiopods with both or at least one of the chelae of a specific subspatulate shape, with fingers generally longer than palm. Further, the species of the latter group share a similar shape of rostrum, and position of the carapacial teeth, subspatulate first pereiopod chela, short carpus of second pereiopods, simple ambulatory dactyli with elongate sharp unguis, and the shape and spinulation of the male pleopods ( Bruce 1989).

Zenopontonia as well as other related echinoderm-associated taxa, such as Periclimenes colemani Bruce, 1975, and Lipkemenes lanipes (Kemp, 1922), are generally also very similar to Actinimenes by the position of antennal and hepatic teeth, an incised transverse ridge on the fourth thoracic sternite, the deeply subspatulate chelae of the first pereiopod, the shape of the chela of the second pereiopod and the very short carpus, and by the shape and spinulation of the male pleopods ( Bruce 1989). These species however differ from Actinimenes spp. by a more down curved rostrum, more posteriorly situated and smaller dorsal telson spines, fine pectination on the fingers of the first pereiopod, and the ambulatory dactyli having small distoventral tooth on the corpus, sometimes also fully reduced ( Marin 2012). Some mollusc- or ascidian-associated genera, e.g. Anchistus Borradaile, 1898, Paranchistus Holthuis, 1952, or Dasella Lebour, 1945, show some phylogenetic relationship to these echinoderm associated taxa ( Gan et al. 2015, Horká et al. 2016), and thus more remotely also to Actinimenes gen. n. All species of these genera differ however from Actinimenes gen. n. by specialized biunguiculate ambulatory dactyli.

The three species of Actinimenes gen. n. were previously thought to be part of the ' Periclimenes brevicarpalis group’ ( Bruce and Svoboda 1983, Bruce 2010), although Fransen (1989) regarded them as comprising a ' Periclimenes inornatus group’ of identical composition of the new genus (see also Remarks for Ancylocaris brevicarpalis comb. n., above).

Distribution.

Widely distributed in the Indo-West Pacific from the Red Sea and Kenya to Japan, Marshall Islands, and Fiji.

Ecology.

The species of the present genus are all obligate associates of sea anemones ( Cnidaria: Actiniaria ) (see Fransen 1989, Müller 1993).

Key to species identification of Actinimenes gen. n.