Richalpheus alpheoides, Anker, Arthur, 2011

Anker, Arthur, 2011, Description of a third species in the alpheid shrimp genus Richalpheus Anker & Jeng, 2006 (Crustacea, Decapoda), Zootaxa 3059, pp. 59-68 : 61-66

publication ID	https://doi.org/ 10.5281/zenodo.278924
DOI	https://doi.org/10.5281/zenodo.3510436
persistent identifier	https://treatment.plazi.org/id/03DC87F7-137B-FFAE-D7D2-FCD8433DFCDA
treatment provided by	Plazi
scientific name	Richalpheus alpheoides
status	sp. nov.

Treatment

Richalpheus alpheoides View in CoL sp. nov.

( Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Richalpheus palmeri View in CoL . — Anker 2010: 34 View Cited Treatment , figs. 7, 8 (not R. palmeri Anker & Jeng, 2006 View in CoL ).

Type material. Holotype: ovigerous female (cl 4.05 mm), MNHN-IU-2011-5235, Egypt, Red Sea coast, 15 km north of Safaga, Soma Bay, sand flat near small fringing coral reef, some Caulerpa , in burrow, yabby pump, 0.5–1 m, leg. A. Anker, 0 4.09.2009 [fcn EG-028].

Additional material. 1 female (CL 3.35 mm), FLMNH UF Arthropoda 16524, French Polynesia, Society Archipelago, Moorea, lagoon between Papetoai and Hotel Inter-Continental, sand flat with mounds and some rubble, nearby coral heads, abundance of Holothuria atra Jaeger , in burrow, yabby pump, 0.5–1 m, leg. A. Anker, 23.11.2008 [fcn BMOO-5632].

Description. Carapace smooth; frontal margin broadly rounded, descending in lateral view; pterygostomial angle rounded, not protruding anteriorly; branchiostegial margin with pronounced lip anteriorly ( Fig. 1 View FIGURE 1 A, B). Sixth abdominal somite with slight suture at posteroventral angle, without distinct articulated plate ( Fig. 1 View FIGURE 1 C). Telson widest in proximal third, distally slightly tapering; dorsal surface with two pairs of strong spiniform setae inserted in deep pits at some distance from lateral margin, anteriorly and posteriorly to telson mid-length, respectively; posterior margin with two pairs of stout spiniform setae at posterolateral angles, mesial much longer and stouter than lateral; anal tubercles feebly developed ( Fig. 1 View FIGURE 1 D).

Eyes completely concealed in dorsal and lateral views, partly visible in frontal view; anteromesial margin of eyestalks rounded; corneas relatively small, but well-pigmented ( Fig. 1 View FIGURE 1 A, B).

Antennular peduncles moderately stout, flattened dorsoventrally; first article with dorsomesial margin bearing a short row of small spiniform setae; stylocerite pressed against peduncle, tip free-standing, subacute, not reaching distal margin of first article; ventromesial carina with large, anteriorly rounded tooth; second article at most 1.5 times as long as wide; lateral flagellum with short secondary ramus carrying at least five tufts of aesthetascs ( Fig. 1 View FIGURE 1 A, E). Antennal basicerite moderately stout, with small distoventral tooth; scaphocerite ovate, with small, subacute distolateral tooth reaching only slightly beyond anterior margin of blade, latter slightly angular anteriorly; carpocerite reaching well beyond scaphocerite, but not beyond end of antennular peduncle ( Fig. 1 View FIGURE 1 A, B, F).

Mouthparts typical for genus in external view. Third maxilliped with lateral plate on coxa bluntly produced dorsally; exopod long, reaching beyond distal margin of antepenultimate article; penultimate and especially ultimate article more slender, latter with unarmed tip; arthrobranch large ( Fig. 1 View FIGURE 1 G).

Major cheliped elongate, relatively slender, chela folded against merus when not in use; ischium very short, unarmed; merus depressed ventrally; ventrolateral margin ending in blunt distal tooth; carpus short, cup-shaped; chela with smooth, ventromesially depressed palm; dorsal face with deep transverse constriction near articulation with dactylus; fingers about 0.6 palm length, somewhat twisted, gaping when closed, tips touching, but not strongly crossing; cutting edge of dactylus with well-defined, somewhat molar-shaped tooth in proximal half, distal surface of this tooth shallowly excavated; cutting edge of pollex with rounded fossa opposed to dactylar tooth ( Fig. 2 View FIGURE 2 ).

Minor cheliped slender, chela folded against merus when not in use; merus slender, ventrally flattened; carpus small, cup-shaped; chela, slender, with palm smooth, somewhat depressed mesially; fingers about 1.5 times longer than palm, slender; tips crossing; cutting edges with minute, widely spaced, subacute teeth, mostly in proximal half ( Fig. 1 View FIGURE 1 H–J).

Second pereiopod relatively short; merus as long as carpus; carpus four-articulated, article ratio approximately equal to 4: 1: 1: 1: 2 ( Fig. 1 View FIGURE 1 K). Third pereiopod and fourth pereiopods similar; ischium short, unarmed; merus with convex ventral margin, more than three times as long as greatest width; carpus short, less than half length of merus, with stout distoventral spiniform seta; propodus with three spiniform setae along ventral margin (including distal); dactylus slightly more than half length of propodus, simple, conical, acute distally ( Fig. 1 View FIGURE 1 L). Fifth pereiopod much shorter and more slender than third and fourth; propodus with five setal rows distolaterally ( Fig. 1 View FIGURE 1 M).

Uropod with lateral lobe of protopod ending in two small spaced teeth; exopod with distolateral margin incised; diaeresis with feebly marked, broadly triangular tooth adjacent to spiniform seta, and two much larger triangular teeth fringing deep mesial incision; distolateral margin broadly incised, as illustrated ( Fig. 1 View FIGURE 1 N).

Size. The female holotype is 4.05 mm cl; the female from Moorea is only slightly smaller, at 3.35 mm cl.

Colour in life. Semitransparent, whitish, with faint pinkish tinge and scattered red chromatophores; cheliped hyaline-white; eggs or ovaries pale green in the Safaga female, pale yellow in the Moorea female ( Figs. 3 View FIGURE 3 , 4 View FIGURE 4 ; see also Anker 2010: fig. 8).

Etymology. Refers to the fingers of the major chela with a tooth-fossa system similar to the snapping mechanism of Alpheus Fabricius, 1798 ( alpheoides = Alpheus -like); used as adjective.

Type locality. Red Sea coast of Egypt: Soma Bay 15 km north of Safaga.

Distribution. Indo-West Pacific: presently known only from two very distant localities, the type locality in the northern Red Sea (near Safaga, Egypt) and Moorea Island, French Polynesia.

Ecology. Both the Safaga and the Moorea specimens were collected on a shallow sand flat near fringing coral reef or scattered branching and massive corals; associated commensally with burrows of unknown hosts.

Remarks. The three presently known species of Richalpheus can be distinguished by the configuration of the fingers of the major cheliped. In R. alpheoides sp. nov., the dactylus has a well-defined, distally excavated tooth, situated in the proximal half of the dactylar cutting edge, and fitting into a deep rounded fossa on the pollex ( Fig. View FIGURE 2

2D–F); see also Anker 2010, tooth partly visible in fig. 8E). In R. palmeri , the dactylus has a broad bulge-like tooth, situated at about half-length of the dactylar cutting edge and fitting into a deep rounded fossa on the pollex (Fig. 7E; see also Anker & Jeng 2006: fig. 4). In R. dahabensis , the dactylus has neither a bulge nor a tooth, whereas the pollex has a proximal groove instead of a well-marked rounded fossa ( Anker & Dworschak 2007: fig. 3A). In addition, R. alpheoides sp. nov. differs from R. palmeri and R. dahabensis by the shorter antennular peduncles (especially in the ratio of second article), the more deeply incised distolateral margin of the uropodal exopod, and the mesioventral carina of the first article of the antennular peduncle ending in a blunt tooth (cf. Fig. 1 View FIGURE 1 and figures in Anker & Jeng 2006; Anker & Dworschak 2007).

Richalpheus alpheoides sp. nov. is presently the only species of Richalpheus with a tooth-fossa system reminiscent of that of true snapping shrimps, i.e. mainly species of by far the largest alpheid genera, Alpheus Fabricius, 1798 and Synalpheus Bate, 1888 . A similar tooth-fossa system is also found in the more distantly related Amphibetaeus jousseaumei Coutière, 1897 . However, in A. jousseaumei , the dactylar tooth and the pollex fossa are much more distal, and the cutting edges of the dactylus and pollex are armed with additional teeth: a proximal tooth on the dactylus and a proximal tooth plus a distal one on the pollex ( Anker & Jeng 2006: fig. 9). Presently it remains unknown whether R. alpheoides sp. nov. and A. jousseaumei are actually capable of snapping.

The holotype female carries a two-dozen or so fairly large embryos ( Fig. 3 View FIGURE 3 A), suggesting an abbreviated larval development. Also noteworthy, Dahab, the type locality of R. dahabensis is less than 200 km away from Safaga, the type locality of R. alpheoides sp. nov., suggesting that that these two species probably occur sympatrically on the coasts of the northern Red Sea.