Alpheus crockeri Armstrong 1941

Alpheus crockeri (Armstrong, 1941)

(Fig. 4)

Crangon crockeri Armstrong 1941: 8, figs. 2, 3.

Alpheus crockeri— Crosnier & Forest 1965: 603; Crosnier & Forest 1966: 225, figs. 4, 5; Manning & Chace 1990: 14; Hayashi 1998: 46, figs. 342c, 343c, 344c, h; De Grave et al. 2014: 5.

Crangon tuthilli Banner 1953: 63, fig. 19.

Alpheus tuthilli — Banner 1956: 338, fig. 9.

Material examined. Brazil: 1 male, MZUSP 30060, Trindade Island, Enseada da Cachoeira, Praia do M, 20°30’53.8”S – 29°20’19.2”W, depth: 15 m, coll. J.B. Mendonça, 08.vii.2013; 1 ovig. female, MZUSP 33251, Trindade Island, Enseada dos Portugueses, Ponta da Calheta, 20°30’18.7”S – 29°18’31.6”W, depth: 13.9 m, ARS, coll. J.B. Mendonça, 05.xi.2014; 1 female, MZUSP 33261, same collection data; 1 male, 1 female, OUMNH.ZC. 2016.02.0 13, Enseada dos Portugueses, Farol, 20°29’52.3”S – 29°19’15.6”W, depth: 12.6 m, coll. J.B. Mendonça, 06.vii.2015; 1 male (?, missing major cheliped and both endopods on second pleopods), MZUSP 33254, Trindade Island, Enseada Orelhas, 20°29’40.2”S – 29°20’32.9”W, depth: 12 m, coll. J.B. Mendonça, 01.xi.2014; 1 female, MZUSP 33408, Trindade Island, Enseada Orelhas, 20°29’40.2”S – 29°20’32.9”W, depth: 12 m, coll. J.B. Mendonça, 01.xi.2014; 1 juvenile, MZUSP 30043, Trindade Island, Ponta Norte, 20°29’18.7”S – 29°20’18.3”W, depth: 15.6 m, coll. J.B. Mendonça, 03.vii.2012; 1 male, MZUSP 34121, Trindade Island, Enseada da Cachoeira, Farrilhões, 20°31’29.8”S – 29°19’52.0”W, depth: 17 m, coll. J.B. Mendonça, 23.vii.2015; 1 female, MZUSP 31499, TAAF MD55 / Brésil 1987 campaign, sta. 20/DC34, Espírito Santo, off Vila Velha, Vitória-Trindade Seamount Chain, 20°28’S – 36°54’W, depth: 50 m, 15.v.1987. Size of largest male: cl 6.5 mm (OUMNH.ZC. 2016.02.013); largest female: cl 6.5 mm (MZUSP 33251).

Additional (extra-limital) material examined. São Tomé and Príncipe: 1 male, MZUSP 34505, São Tomé Island, Praia Lagarto, near São Tomé hospital, sand flat with Montastrea, zoanthids and rocks embedded in sand, intertidal (extreme low tide), coll. A. Anker & N. Knowlton, 30.i.2006 [fcn 06-015]; 1 male, OUMNH.ZC. 2016.02.0 14, São Tomé Island, Ilhéu de Santana, depth 15–20 m, under rocks and rubble and from rock crevices, coll. N. Knowlton & F. Nunes 09.ii.2006 [fcn 06-197]; 1 ovig. female, OUMNH.ZC. 2016.02.0 15, same collection data [fcn 06-196]; 1 ovig. female, OUMNH.ZC. 2016.02.0 16, same collection data [fcn 06-198]; 1 ovig. female, MZUSP 34506, São Tomé Island, ~ 4 km west of Lagoa Azul, shallow subtidal, depth: 0.5–2 m, under rocks, coll. A. Anker, 17.ii.2006 [fcn 06-244]; 1 ovig. female, OUMNH.ZC. 2016.02.0 17, same collection data [fcn 06-247]. Japan: 1 ovig. female, OUMNH.ZC. 2016.02.0 18, Ryukyu Archipelago, Yaeyama Islands, Ishigaki-jima, Sakieda, 24°25’ 18.37’’N 124°04’ 40.40’’E, depth: 18 m, under dead coral, coll. K. Nomura, 20.viii.1998 [fcn YMP-2046]; 1 male, OUMNH.ZC. 2016.02.0 19, Ryukyu Archipelago, Yaeyama Islands, Hateruma-jima, in front of Hateruma Port, 24°04’ 21.51’’N 123°45’ 49.12’’E, depth: 10 m, under dead coral, coll. K. Nomura, 05.vii.1998 [fcn YMP- 1963]. French Polynesia: 1 male, OUMNH.ZC. 2016.02.0 20, Society Islands, Moorea, Opunohu Bay, depth: 4 m, in dead Pocillopora colony, coll. M. Leray, 11.viii.2009 [fcn 1108-C-002].

Comparative material examined. Alpheus hortensis Wicksten & McClure, 2003. USA: holotype, female, USNM 1014084, Texas, West Flower Garden Bank, Stetson Bank, 28°10'N – 94°17'W, near Buoy Nr 2, depth: 21- 24 m, in hole in shale rubble, coll. M.K. Wicksten, 26.vi.2001.

Description. See Armstrong (1941) for original description and illustrations of A. crockeri; Crosnier & Forest (1966) for description and illustrations of the eastern Atlantic material; and Banner (1953, 1956) for additional figures of the western Pacific material (as Alpheus tuthilli (Banner, 1953)).

Distribution. Almost pantropical (apparently absent only in the eastern Pacific). Amphi-Atlantic: São Tomé & Príncipe; Equatorial Guinea: Annobon Island; Ascension Island; Brazil: Vitória-Trindade Seamount Chain and Trindade Island (Crosnier & Forest 1966; Manning & Chace 1990; De Grave et al. 2014; present study). Indo-West Pacific: from Réunion Island to Japan, Hawaii and Easter Island (Rapa Nui) (Armstrong 1941; Banner & Banner 1983; Chace 1988; Di Salvo et al. 1988; Hayashi 1998).

Ecology. Coral reefs and adjacent habitats rich in coral rubble or clumps of coralline algae; typically under rocks and coral rubble or among coralline algae; depth range: 1– 50 m.

Remarks. Alpheus crockeri is presently considered as a widespread, almost pantropical species, with populations across the Indo-West Pacific and Atlantic Oceans. In the Atlantic Ocean, A. crockeri was previously known from São Tomé and Annobon Islands in the Gulf of Guinea, and Ascension Island on the mid-Atlantic ridge. The finding of A. crockeri off Espírito Santo (Vitória-Trindade Seamount Chain) and around Trindade Island is interesting in view of the presence of its presumed sister species, A. hortensis Wicksten & McClure, 2003, in the northern Gulf of Mexico (Wicksten & McClure 2003).

Wicksten & McClure (2003) used three morphological characters to separate A. hortensis from A. crockeri: (1) the distal armature of the minor chela palm (with blunt teeth in A. hortensis vs. with sharp teeth overhanging dactylar base in A. crockeri); (2) the proportions of the fingers to the palm in the minor cheliped (fingers slightly shorter than palm in A. hortensis vs. slightly longer than palm in A. crockeri); and (3) the length of the posterolateral spines of the telson (proportionally longer in A. hortensis than in A. crockeri). The material from Trindade was identified as A. crockeri based on the first two criteria. However, the length of the posterolateral spines of the telson was found to be more or less as illustrated by Wicksten & McClure (2003) for A. hortensis, at least in some specimens. Therefore, this last character probably cannot be used to separate these two taxa. The first character, i.e. the presence of a sharp distal teeth on the minor chela palm, was also used by De Grave et al. (2014) to identify the material from Ascension Island as A. crockeri. Importantly, Rodríguez’s (1986) female specimen from Los Roques, Venezuela, also had a sharp distal tooth on the minor chela palm and therefore may well correspond to A. crockeri and not A. hortensis, as suggessted by Wicksten & McClure (2003); therefore, the western Atlantic range of A. crockeri may well extend into the Caribbean Sea. In addition, the minor chela of the holotype of A. hortensis bears a subacute distal tooth on the lateral side of the palm (A. Anker, pers. obs.), making this character too ambiguous for distinction between A. crockeri and A. hortensis, which seriously jeopardises the validity of the latter species. The almost uniform yellow colouration of A. crockeri from Trindade Island (Fig. 4), which also characterises specimens from São Tomé and the Indo-West Pacific (A. Anker, pers. obs.), seems to be identical to that of A. hortensis (cf. Wicksten & McClure 2003: fig. 1).

The Atlantic material identified here as A. crockeri was also compared to the material from the Indo-West Pacific, from where the species was originally described (type locality: Samoa). A direct morphological comparison between specimens from Trindade Island, São Tomé Island, Japan and French Polynesia (see comparative material) revealed some differences, but none of them appeared to be consistent and thus taxonomically significant. The proportions of the minor cheliped, e.g. the length of the fingers relative to the palm and the length-width ratio (thickness) of the palm, as well as the relative length-width ratio of the merus, were initially noted as possible differences of taxonomic importance (compare figures in Crosnier & Forest 1966: fig. 5f; Armstrong 1941: fig. 2c; Banner 1956: fig. 9). However, after examination of the present material, these proportions were found to be variable within the Indo-West Pacific and Atlantic populations. Although the Atlantic specimens generally seem to have a stouter palm with shorter fingers compared to the Indo-West Pacific specimens, a few exceptions, e.g. a large ovigerous female from São Tomé with a relatively slender minor chela (OUMNH.ZC. 2016.02.014) and a male from the Ryukyu Islands in southern Japan (OUMNH.ZC. 2016.02.015) with a relatively stout one, do not allow to use this character to unambiguously separate the Atlantic and Indo-West Pacific materials. Similarly, the difference in the proportions of the minor cheliped merus, which is rather obvious in the figures provided by Crosnier & Forest (1966: fig. 5f) and Banner (1956: fig. 9), was not very clear in the present material.

In conclusion, the Atlantic material of A. crockeri does not seem to differ morphologically from the Indo-West Pacific material, suggesting that there may be indeed a single widespread species. The taxonomic status of A. hortensis, which seems to differ from A. crockeri rather subtly, if at all, needs to be investigated further, starting with a re-examination of the entire type series of the species. More generally, a thorough molecular comparison between the Atlantic specimens of A. crockeri and A. hortensis, as well as the Indo-West Pacific material of A. crockeri, seems unavoidable to achieve a final conclusion for both taxa.