Metabetaeus lohena Banner & Banner, 1960

Anker, Arthur, 2010, Metabetaeus Borradaile, 1899 revisited, with description of a new marine species from French Polynesia (Crustacea: Decapoda: Alpheidae), Zootaxa 2552, pp. 37-54 : 51-53

Metabetaeus lohena Banner & Banner, 1960

Figs. 10 , 11 B, C

Metabetaeus lohena Banner & Banner 1960c: 299 , fig. 1; Holthuis 1963: 270; Holthuis 1973: 35; Banner & Banner 1974: 427; Holthuis 1986: 608; Anker 2009: 7, figs 2c, 3d, e, 5f, g, 6; Russ et al. 2010: 160. Metabetaeus lohena – Banner & Banner 1985: 35.

Metabetaeus cf. lohena – Anker 2009: 11.

Material examined. 21 specimens of both sexes (cl 2.5–8.0 mm, tl 7.2–21.5 mm), OUMNH.ZC- 2010-20 - 0 0 9, Rapa Nui (Easter Island), Hanga Tetenga coastal well, submitted to tidal oscillation, covered with a concrete slab, baited trap, coll. G. Boxshall and J. Daume, 25 November 2004 (note: specimens fixed in formalin, transferred to 75% ethanol).

Description. The Rapa Nui specimens generally agree with the description of the type series from Hawaii (see Banner & Banner 1960), except for the somewhat more robust chelipeds (compare Figs. 10 A, B and Fig. 10 C, D; see also remarks below).

Size range. The largest specimen from Rapa Nui is a female at cl 8.0 mm, tl 21.5 mm; the female holotype of M. lohena measured tl 16.6 mm ( Banner & Banner 1960).

Colour pattern. Specimens from Hawaii: as in M. minutus , variable from dull pink to bright red or redorange, depending on the contraction state of numerous red chromatophores organised in broad bands on the abdomen ( Fig. 9 B, C).

Ecology. The present specimens were found in an anchialine “coastal well” with tidal influence; in Hawaii, M. lohena occurs only in anchialine lava pools; for detailed notes on habitat and biology see Banner & Banner (1960), Holthuis (1963, 1973), and summary in Anker (2009).

Type locality. Anchialine pools at Lohena Rock, Hawai’i, Hawaiian Archipelago.

Distribution. Indo-West Pacific, localised, presently known only from Hawaiian Archipelago, viz. Hawai’i (e.g., Lohena Rock, Kona), Maui (e.g., Cape Kinau) and Oahu (see Banner & Banner 1960, 1974; Holthuis 1973; Russ et al. 2010); Rapa Nui: Hanga Tetenga (present study); and Ambon, Indonesia: Rumah Tiga ( Banner & Banner 1985) ( Fig. 12 ).

Remarks. Banner & Banner (1960) separated M. lohena from M. minutus based mainly on the length of the stylocerite and the proportions of the chelae in adults (especially the length and curvature of the fingers). Later, the same authors ( Banner & Banner 1983) recognised that the length of the stylocerite is variable in both M. lohena and M. minutus , and concluded that these two species can be effectively separated from each other only by their chelipeds.

The material from Rapa Nui is somewhat problematic. In most specimens, chelipeds are lost or are detached but present in the vial. The largest specimen, a female (cl 8.0 mm) has no chelipeds; however, two equal and subsymmetrical chelipeds matching her size are present in the vial; one of them is illustrated ( Fig.10 A. B). The ratio of the chela to the fingers is much closer to M. lohena than to M. minutus , although both the chela and the fingers appear to be stouter than in M. lohena from Hawaii (see Fig. 10 ). Further complicating the identification issues, Saavedra et al. (1996) also recorded M. minutus from Rapa Nui; all specimens were found in a single anchialine pool, situated 25 m from the coastline, without apparent connection to the sea. Based on a few drawings provided by Saavedra et al. (1996, figs. 2–3), their specimens could be either M. minutus or younger individuals of M. lohena . Additional specimens from Rapa Nui and a comparison of COI haplotypes between Hawaiian and Rapa Nui populations will hopefully soon clarify the status of the Rapa Nui populations of M. lohena . Some preliminary genetic data on M. lohena was recently provided by Russ et al. (2010), who sequenced COI from 127 specimens of M. lohena collected at different anchialine pools across the islands of Hawai’, Maui and Oahu. These authors found very little genetic structure in M. lohena , suggesting either a very efficient oceanic dispersal or a relatively recent invasion of the Hawaiian Archipelago.

Figures

FIGURE 9. Metabetaeus minutus (Whitelegge, 1897), male from Runaway Cave, Christmas Island (ZRC 2010.0013): A, frontal margin of carapace, dorsal; B, frontal region of carapace and frontal appendages, lateral; C, left cheliped, lateral; D, same, chela, mesial; E, second pereiopod, lateral; F, third or fourth pereiopod (detached), lateral; G, fifth pereiopod, lateral.

FIGURE 10. Metabetaeus lohena Banner & Banner, 1960, female from Rapa Nui (OUMNH. ZC- 2010 - 20 - 009): A, right cheliped, lateral; B, same, chela, mesial; paratype from Hawaii: C, left cheliped, lateral; D, same, chela, mesial (C, D after Banner & Banner 1960).

FIGURE 11. Metabetaeus minutus (Whitelegge, 1897), male from Runaway Cave, Christmas Island (ZRC 2010.0013): A, habitus, lateral. Metabetaeus lohena Banner & Banner, 1960 from Hawai’i (not deposited): B, C, two individuals from anchialine pond at Kona, Kaloko-Honokohau National Park, Hawai’i, showing different state of contraction of chromatophores (photographs: Peter K. L. Ng [A]; Karl Magnacca [B, C]).

FIGURE 12. Current distribution of the genus Metabetaeus Borradaile, 1899 (see text for details).