Ancylocaris Schenkel, 1902

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 : 25-28

Genus Ancylocaris Schenkel, 1902

Type species.

Ancylocaris brevicarpalis Schenkel, 1902, by monotypy.

Included species.

Ancylocaris brevicarpalis Schenkel, 1902 (Figs 1, 3A, B).

Gender.

Feminine.

Diagnosis.

Subcylindrical body form. Carapace smooth; rostrum well developed, subequal to antennular peduncle and moderately high, dorsal margin convex, dentate, with first tooth postorbital, ventral margin convex, with 1-2 teeth on distal third of rostrum length. Inferior orbital angle produced, without reflected inner flange, supraorbital and epigastric teeth absent, antennal and hepatic teeth present. Fourth thoracic sternite with broad transverse ridge subdivided by deep narrow median incision. Pleon smooth, third tergite non-carinated or posteriorly produced, pleura 1-5 posteroventrally rounded; telson with 2 pairs of minute dorsal spines on distal third of telson length and 3 pairs of short posterior marginal spines. Ophthalmic somite without interocular process. Antennule and antenna as usual for the family; upper ramus of antennular flagellum biramous, with fused basal part; scaphocerite moderately broad, with small distolateral tooth falling short of anterior margin of lamina; carpocerite short. Eyes with small accessory pigment spot dorsally on corneal margin. Mandible without palp; molar and incisor processes normal. Maxilla with basal endite distinctly bilobed, coxal endite obsolete, scaphognathite normal; first maxilliped with endites fused, exopod well developed, with multiple terminal setae, caridean lobe normal, epipod feebly bilobed; second maxilliped with normal endopod, exopod as in first maxilliped, without caridean lobe, epipod small, simple, without podobranch; third maxilliped with slender endopod, ischiomerus fused or feebly separated from basis, exopod as in second maxilliped, coxa with semi-circular lateral plate, single arthrobranch present. First pereiopods slender, coxa with distomedial setose lobe, fingers of chelae elongate, with lateral cutting edges. Second pereiopods moderately stout, similar and subequal, chelae with fingers kept laterally; fingers subequal to palm, cutting edges with simple lamina and 2 low proximal teeth, carpo-propodal articulation simple, carpus much shorter than palm in adults, feebly cup-shaped. Ambulatory pereiopods slender, propodus without ventral spines, dactyli with minute or reduced distoventral tooth on stout corpus, unguis elongate, curved. Endopod of male first pleopod simple, elliptic, with multiple spinules medioproximally and multiple pappose setae distally. Male second pleopod with appendix masculina slender, with several simple terminal and lateral setae. Uropods normal.

Figures

(selected). Schenkel (1902: Pl. 13, fig. 21), Kemp (1922: figs 40-42, Pl. 6, fig. 8), Kubo (1940: figs 13-14), Miyake and Fujino (1968: fig. 4), Bruce (1978: fig. 6; 1979: Pl. 1, fig. A), Fransen (1989: fig. 1 a–c).

Systematic position.

Ancylocaris brevicarpalis (under the name Periclimenes brevicarpalis ), together with Periclimenes inornatus Kemp, 1922, Periclimenes nevillei Bruce, 2010, Periclimenes ornatus Bruce, 1969, Periclimenes ornatellus Bruce, 1979, and Periclimenes albolineatus Bruce & Coombes, 1997, were previously believed to be members of a " Periclimenes brevicarpalis " group (see Bruce and Svoboda 1983, Bruce and Coombes 1997, Bruce 2010) some of which are sea anemone associated species. On the contrary, Fransen (1989) stated that only three of those species, i.e. Periclimenes inornatus , Periclimenes ornatellus , and Periclimenes ornatus , are closely related to each other and comprise a " Periclimenes inornatus " group (see Actinimenes gen. n., below), rather than belong in the " Periclimenes brevicarpalis " group. The available comprehensive molecular phylogenies ( Gan et al. 2015, Horká et al. 2016) show that at least Ancylocaris brevicarpalis (under the name Periclimenes brevicarpalis ) occupies a position away from the Periclimenes inornatus group.

While the species of the " Periclimenes inornatus " group share with Ancylocaris the general shape of the body, especially of the rostrum and the second pereiopods, they may easily be distinguished from Ancylocaris brevicarpalis by the presence of deeply subspatulate chelae of the first pereiopod, but also by the more numerous proximal teeth on the fingers of the second pereiopod, as well as larger and more anteriorly placed dorsal telson spines (the first pair before mid-length). The propodal segment of the second maxilliped in Ancylocaris brevicarpalis is broader than the dactylus and distomesially expanded, while sub-equally broad in the " Periclimenes inornatus " group (e.g. Kubo 1940, Bruce 1979).

The sister taxon for Ancylocaris , as revealed by the analyses of Gan et al. (2015) and Horká et al. (2016), is actually a pair of Periclimenes species, the crinoid-associated Periclimenes affinis (Zehntner, 1894) and Periclimenes kallisto Bruce, 2008, which is symbiotic with antipatharian corals. The significant genetic distance of this pair however indicates that their position is most likely quite distant from Ancylocaris . Both those species show some resemblance to Ancylocaris brevicarpalis in the size and position of the dorsal telson dentition, and in the distomedial coxal lobe and fingers on the first pereiopods. Periclimenes affinis also has a short carpocerite and a similar carpus of the second pereiopod, and similar male pleopod shape and setation. Periclimenes kallisto has feeble dentition of the fingers of the second pereiopod and the ambulatory dactyli with a minute distoventral tooth. These two species are more slender and smaller than Ancylocaris brevicarpalis and bear a slender rostrum with obsolete ventral carina, unequal second pereiopods, ventrally spinulose ambulatory propodi, and the endopod of the male first pleopod has a distomedial lobe ( Holthuis 1958, Bruce 1980, 2008a). A close affinity between these two species was suggested by Bruce (2008a), who highlighted a group of species of a similar morphology, additionally including Periclimenes canalinsulae Bruce & Coombes, 1997, and Periclimenes jugalis Holthuis, 1952. Some other taxa, for instance Periclimenes novaffinis Bruce & Coombes, 1997, Periclimenes albolineatus and Periclimenes nevillei , may also belong to this group. The systematic relation of this assemblage as well as of each particular member to the genus Ancylocaris remains to be resolved.

Remarks.

The earliest report on the present species was published by Zehntner in 1984. However, Holthuis (1952) places Palaemonella amboinensis Zehntner, 1894 into the synonymy of Ancylocaris brevicarpalis Schenkel, 1902 under the name Periclimenes brevicarpalis (Schenkel, 1902), as he considers the drawing of the scaphocerite and the antennular peduncle in Zehntner (1894) not to be entirely correctly drawn. After the examination of a photograph of the holotype (Fig. 1) kindly provided by L. Monod (MHNG) we fully concur with this position. Palaemonella amboinensis Zehntner (1894) should thus have priority over Periclimenes brevicarpalis (Schenkel, 1902); however as stated by Holthuis (1952) the latter name is preoccupied by Periclimenes amboinensis (De Man, 1888), originally described as Anchistia amboinensis De Man, 1888. For some time now both taxa are no longer considered congeneric, as Anchistia amboinensis De Man, 1888 was placed in the genus Laomenes AH Clark, 1919, resurrected for a group of crinoid dwelling species by Okuno and Fujita (2007). Conversely, Ancylocaris brevicarpalis Schenkel, 1902 was maintained in the genus Periclimenes up to now, although now returned to the resurrected genus Ancylocaris . This creates some ambiguity as to what is the correct name for the taxon currently known as Periclimenes brevicarpalis (Schenkel), a rather widespread, well-known and often photographed species.

Article 60.1 ( ICZN 1999) specifies that a junior homonym must be rejected and replaced either by an available and potentially valid synonym or, for lack of such a name, by a new substitute name. We herein interpret Holthuis’s (1952) action in proposing to use a junior synonym, Ancylocaris brevicarpalis Schenkel, 1902, for Palaemonella amboinensis Zehntner, 1894 as a "substitute name". In which case, Art. 59.3 specifies "that a junior secondary homonym replaced before 1961 is permanently invalid unless the substitute name is not in use and the relevant taxa are no longer considered congeneric, in which case the junior homonym is not to be rejected on grounds of that replacement". Clearly, the substitute name, Periclimenes brevicarpalis (Schenkel) is in widespread use, throughout the scientific literature as well as popular accounts, as it is one of the most photographed shrimp species. Even though both taxa have not been considered congeneric since the resurrection of the genus Ancylocaris makes Ancylocaris brevicarpalis Schenkel, 1902 the valid name for the species in question.

Distribution.

The single species in the genus is widely distributed throughout the whole Indo-West Pacific, from South Africa and Red Sea to Japan and Polynesia.

Ecology.

Ancylocaris brevicarpalis is obligatory associated with sea anemones ( Cnidaria: Actiniaria ) (cf. Fransen 1989, Müller 1993), although juveniles may also occur on alcyonarian and scleractinian corals.