Alpheus baccheti, Anker, Arthur, 2010

Anker, Arthur, 2010, On two snapping shrimps, Alpheus baccheti n. sp. and A. coetivensis Coutière from the Tuamotu Islands, French Polynesia (Crustacea, Decapoda), Zootaxa 2492, pp. 49-62 : 50-58

publication ID	https://doi.org/ 10.5281/zenodo.195661
DOI	https://doi.org/10.5281/zenodo.6206825
persistent identifier	https://treatment.plazi.org/id/03A887FC-FF9E-D62C-38B2-FEB0FE9D248A
treatment provided by	Plazi
scientific name	Alpheus baccheti
status	sp. nov.

Treatment

Alpheus baccheti View in CoL n. sp.

Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5

Material examined.— Holotype, male (CL 13.5 mm), FLMNH UF Arthropoda 18556, French Polynesia, Tuamotu Islands, Makemo, lagoon, reef flat, around 0.5 m at low tide, coll. P. Bacchet and J. Letourneux, April 2009.

Description.—Medium-sized species of Alpheus edwardsii group. Carapace glabrous, not setose. Rostrum conical, with pointed tip, latter reaching to distal margin of first segment of antennular peduncle ( Fig. 1 View FIGURE 1 b); rostral carina feebly developed, rounded dorsally, flattening between orbital hoods ( Fig. 1 View FIGURE 1 a); orbital hoods swollen, gradually sloping into shallow adrostral area, with rounded anterior margin. Ventro-rostral process moderately developed. Pterygostomial angle not protruding anteriorly, rounded.

Abdomen with first to fifth pleurae rounded ventrally. Telson relatively broad, subrectangular, tapering posteriorly ( Fig. 1 View FIGURE 1 c); dorsal surface with two pairs of strong spiniform setae situated at some distance from lateral margins, first pair slightly anterior to telson mid-length, second pair at about 0.6–0.7 telson length; lateral margin not constricted, slightly convex; posterior margin broadly rounded, posterolateral angles each with pair of spiniform setae, lateral distinctly longer than mesial ( Fig. 1 View FIGURE 1 d).

Eyes with anteromesial margin not anteriorly protruding; corneas well developed and pigmented. Ocellar beak relatively small, not visible in lateral view. Antennular peduncle with second segment more than 2.5 times as long as wide; stylocerite slightly overreaching distal margin of first segment ( Fig. 1 View FIGURE 1 a); mesioventral carina with low subtriangular tooth ( Fig. 1 View FIGURE 1 f); lateral flagellum with short, stump-like accessory branch and approximately 10 tufts of aesthetascs distally ( Fig. 1 View FIGURE 1 e). Antenna with basicerite armed with sharp distoventral tooth ( Fig. 1 View FIGURE 1 b); scaphocerite moderately long, with broadly concave lateral margin, blade rather narrow and short, overreached by strong distolateral tooth ( Fig. 1 View FIGURE 1 a), latter reaching beyond end of antennular peduncle; carpocerite reaching beyond scaphocerite and end of antennular peduncle ( Fig. 1 View FIGURE 1 b).

Mouthparts typical to Alpheus in external observation. Third maxilliped slender, pediform; lateral plate on coxa acutely protruding; antepenultimate segment not expanded, with even, unarmed ventral margin; ultimate segment very setose ( Fig. 1 View FIGURE 1 g); arthrobranch normally developed.

Major cheliped ( Fig. 2 View FIGURE 2 ) with merus relatively short, stout, bluntly ending dorsally, with strong distinct distal tooth on mesial margin ( Fig. 2 View FIGURE 2 a, b); carpus broadly cup-shaped; chela massive; palm about 1.5 times as long as fingers, distodorsal margin with broad notch extending to lateral and mesial surfaces, and further extending posteriorly ( Fig. 2 View FIGURE 2 a, b), dorsal shoulder not overhanging, rounded, smooth, sloping gradually into notch ( Fig. 2 View FIGURE 2 a-c); distoventral margin with deep, broad notch, ventral shoulder rounded, slightly protruding anteriorly, but not overhanging notch; distomesial margin with rounded lobes; dactylus slightly overreaching pollex, with large plunger, latter with stamen-shaped sensillae ( Fig. 2 View FIGURE 2 c).

Male minor cheliped ( Fig. 3 View FIGURE 3 ) with moderately long merus (proportionally somewhat longer than in major cheliped), dorsal margin ending bluntly, mesial margin with small tooth distally ( Fig. 3 View FIGURE 3 b); carpus cup-shaped; chela with palm approximately 1.2 times as long as fingers; distodorsal margin of palm with shallow constriction (trace of notch), not extending to lateral or mesial surfaces ( Fig. 3 View FIGURE 3 c, d); distoventral margin of palm with distinct notch visible in mesial and especially in lateral view ( Fig. 3 View FIGURE 3 c, d); distomesial margin of palm with stout blunt tooth ( Fig. 3 View FIGURE 3 a, d); dactylus somewhat expanded laterally, with both lateral and mesial ridges bearing dense rows of balaeniceps setae ( Fig. 3 View FIGURE 3 a, c, d); pollex with row of plumose setae on proximal half mesially ( Fig. 3 View FIGURE 3 c), without especially patterned setae laterally ( Fig. 3 View FIGURE 3 d). Female minor cheliped unknown.

Second pereiopod slender; merus subequal in length to ischium; carpus five-segmented, with ratio of segments approximately equal to 3: 3.5: 1: 1: 1.5 ( Fig. 4 View FIGURE 4 a); chela distinctly longer than distal carpal segment. Third and fourth pereipods similar, relatively robust; ischium with small spiniform setae on ventrolateral surface; merus about five times as long as wide, ventral margin armed with sharp tooth ( Fig. 4 View FIGURE 4 b); carpus about half length and 0.7 width of merus, unarmed; propodus longer than carpus but shorter than merus, same with as carpus, ventral margin with 12 spiniform setae inserted either single or in pairs, most distal pair of spiniform setae at propodo-dactylar articulation ( Fig. 4 View FIGURE 4 b, c); dactylus about 0.4 length of propodus, conical, simple ( Fig. 4 View FIGURE 4 c). Fifth pereiopod somewhat shorter and more slender than third and fourth pereiopods; ischium unarmed ( Fig. 4 View FIGURE 4 d); merus, carpus and propodus of same width, merus longer than carpus, unarmed; carpus subequal to propodus, latter with dense rows of setae distally and seven spiniform setae along ventral margin, including one pair of distal spiniform setae adjacent to dactylus ( Fig. 4 View FIGURE 4 e).

Male second pleopod with appendix masculina slightly longer than appendix interna, furnished with stiff setae along margins and on apex ( Fig. 1 View FIGURE 1 h). Uropod with lateral lobe of protopod ending in acute point; diaeresis of exopod sinuous, lateral portion carrying blunt subtriangular lobe adjacent to slender distolateral spiniform seta ( Fig. 1 View FIGURE 1 i); distolateral margin of endopod with row of small spiniform setae ( Fig. 1 View FIGURE 1 j).

Gill formula typical to genus.

Colour pattern.—Carapace opaque whitish with reddish and yellowish chromatophores forming large orange-brown or brown “saddle” covering most of anterior half of carapace and broad transverse band posteriorly; anterolateral angles of carapace more intense red-pink; each abdominal segment with one distinct yellow-orange to cocoa-brown transverse band formed by red chromatophores on yellow background; each bands interrupted laterally by whitish areas; telson and uropods whitish proximally, yellow-orange to dark brown distally; antennular peduncles reddish (densely covered with red chromatophores); antennae proximally with red patches; antennular and antennular flagella pale-yellowish; walking legs (P3–5) and P2 yellowish distally, reddish proximally; major and minor cheliped overall pinkish-red to cocoa-brown, greenish distally; mesial (“dorsal”) side of palm of major chela pink to orange-red, marbled with white areas and patches, with olive-greenish areas distally; pollex olive-greenish distally; dactylus blue-greenish, with white tip; minor chela pinkish with blue-greenish areas on fingers; balaeniceps setae pale golden-brownish ( Fig. 5 View FIGURE 5 ); colour pattern generally much darker brown in situ ( Fig. 5 View FIGURE 5 b) compared to the captured specimen, in which the abdominal bands and tail fan are brighter and more orange-yellow ( Fig. 5 View FIGURE 5 a).

Etymology.—The new species is named after the collector of the holotype specimen, Philippe Bacchet, a marine naturalist and photographer, co-author of the well-known “Guide des poissons de Tahiti et ses îles ” ( Bacchet et al. 2007).

Type locality.—Makemo Island, Tuamotu Islands, French Polynesia.

Distribution.—Presently known only from the type locality in the central region of the Tuamotu- Gambier Archipelago.

Ecology.— Alpheus baccheti n. sp. was collected under a rock or piece of rubble on a reef flat (0.5 m at low tide).

Remarks.—Numerous features on the frontal margin and major chela suggest that A. baccheti n. sp. plainly belongs to the heterogeneous Alpheus edwardsii Audouin, 1826 species group, which is the largest group in the genus Alpheus and clearly non-monophyletic in its present composition ( Williams et al. 2001; Anker et al. 2009). However, the bulk of species currently placed in the A. edwardsii group (e.g., Banner & Banner 1982; Chace 1988) may well form a monophyletic assemblage, temporarily named “clade E” (opposed to “clade L”, see Anker et al. 2009). The new species can be separated from all other species of this clade by the combination of the following features: (1) the frontal margin of the carapace with a posteriorly non-flattened rostrum and rounded, unarmed orbital hoods; (2) the palm of the major chela with a rounded, not overhanging dorsal shoulder and with a rounded, not anteriorly projecting ventral shoulder; (3) the dactylus of the male minor chela furnished with balaeniceps setae; (4) the merus of P3–4 armed with distoventral tooth; and (5) the dactylus of P3–5 being simple, conical (not spatulate or biunguiculate).

The well-developed balaeniceps condition of the male minor cheliped combined and the presence of a strong distoventral tooth on the merus of P3–4 together form a rather unusual character combination not only within the A. edwardsii group s. str. (clade E), but also within the genus Alpheus . The balaeniceps-type dactylus is found in a number of species of the clade E of the A. edwardsii group and does not always reflect their phylogenetic proximity (A. Anker, unpublished data). In addition, this character often but not always is sexually dimorphic; in some cases, both sexes need to be examined to distinguish between closely related species. The only species with P3-4 armed with a strong meral tooth that also has rows of setae on the dactylus of the minor cheliped is A. intrinsecus Bate, 1888 from the Atlantic Ocean, but in this species, the setae seem to be not very dense, while the dactylus is only slightly broadened laterally ( Christoffersen 1979, fig. 10h). In addition, A. intrinsecus differs from A. baccheti n. sp. in a number of other important characters, especially on the major cheliped and rostro-orbital region of the carapace ( Christoffersen 1979, figs. 9–10), and is in fact unrelated to the new species.

Similarly, the presence of a distal tooth on the merus of P3–4 is a feature found in at least 15 species of the clade E (see Table 1). Interestingly, in most of these species, a distal tooth is also present on the carpus; this is not the case of A. baccheti n. sp. In addition, the new species differs from all the other species listed in Table 1 (except for A. intrinsecus , see above) by the balaeniceps condition of the minor chela and more specifically from each of them by the combination of several features on the major chela and rostro-orbital region of the carapace (for comparison see figures in Dana 1855; Nobili 1907; Chace 1972; Banner & Banner 1982, 1983; Kim & Abele 1988; Nomura 2009). In fact, A. baccheti n. sp. does not seem to have close affinities to any of the other species with a meral tooth on P3–4, including the inadequately described and taxonomically problematical A. euchirus Dana, 1852 , A. hoplites Nobili, 1907 , and A. perezi Coutière, 1908 (see Dana 1852; Nobili 1907; Coutière 1908; Banner & Banner 1982). Based on Dana’s (1855) somewhat schematic drawings, A. euchirus may be closely related to A. georgei Banner & Banner, 1982 and A. hippothoe de Man, 1888, both not closely related to A. baccheti n. sp. (see Banner & Banner 1982 for comparison). Alpheus hoplites is another poorly known species characterised by the pointed orbital hoods and a stout biunguiculate dactylus on P3-4, which obviously separate it from A. baccheti n. sp. Similarly, A. perezi was described briefly and without illustrations; according to Coutière (1908), this species may be related to A. pareuchirus Coutière, 1905 , a species complex not related to A. baccheti n. sp. (see Coutière 1905; de Man 1911; Banner & Banner 1982).

TABLE 1. Species of clade E of Alpheus ( A. edwardsii group s. str., see Anker et al. 2009) characterised by the P3–4 armed with a distoventral tooth. Abbreviaitons: P—pereiopod; EA—eastern Atlantic; EP—eastern Pacific; WAwestern Atlantic; IWP—Indo-West Pacific.

On the other hand, A. baccheti n. sp. appears to be phylogenetically closer to several species of the Clade E characterised by the balaeniceps minor chela and rounded orbital hoods, but lacking a distal tooth on the merus of P3-4, in particular to the taxonomically challenging A. lobidens de Haan, 1849 and A. strenuus Dana, 1852 species complexes that together include a dozen or so species in the Indo-West Pacific (A. Anker, unpublished data). This assumption is based on the similar general shape of the rostro-orbital region of the carapace and major and minor chelae, as well as some other characters, such as the presence of a simple, conical dactylus on P3–5. In addition, several species in the A. lobidens and A. strenuus complexes have colour patterns consisting of dark transverse bands on the abdomen (A. Anker, pers. obs.), similar to that of A. baccheti n. sp.