Metabetaeus minutus ( Whitelegge, 1897 )

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 : 48-49

Metabetaeus minutus ( Whitelegge, 1897)

Figs. 8 , 9 , 11 A

Betaeus minutus Whitelegge 1897: 147 , pl. 7, fig. 4a, b.

Metabetaeus minutus – Borradaile 1899: 1014; Coutière 1899: 374; Banner 1957: 193; Banner & Banner 1960: 301, fig. 2; Gressitt 1961: 73; Holthuis 1963: 269; Holthuis 1986: 608; Holthuis 1993: 204; Saavedra et al. 1996: 117 –122, figs. 1b, 2, 3; Miya 1996: 417; Hayashi, 1996f: 488, figs. 312, 313; Komai & Fujita 2005: 23; Anker 2009: 6, figs. 2d, 5c.

Material examined. 1 female (cl 5.8 mm, tl 16.9 mm), FLMNH UF Arthropoda 23251 , Japan, Ryukyu Islands, Minami Daito Jima, Gushi Ken Do, anchialine cave , coll. S. Shokita, 14 October 1979; 2 males (cl 5.95–6.30 mm), 6 females (cl 5.50–7.00 mm), MZB Cru 2605 , Indonesia, Sulawesi, Sulawesi Tenggara, Muna Regency, Tongkuno District, Oempu village, Walengkabola, La Ode Panu cave , 05°10’44.8” S 122°35’02.6” E, anchialine pool inside cave, coll. C. Rahmadi, 13 September 2007 (specimens examined by D. Wowor); 1 male (cl 5.0 mm, tl 13.6 mm), ZRC 2010.0013, Indian Ocean, Christmas Island, Runaway Cave, anchialine pond inside cave , limestone bedrock, loamy substrate, improvised trap (plastic drink bottle), coll. Christmas Island Expedition, 27 January 2010; 1 male (cl 3.3. mm, tl 9.2 mm), 3 females (largest: cl 5.6 mm, tl 16.4 mm), OUMNH.ZC- 2010-20 -010, Loyalty Islands east of New Caledonia, Lifou, Grotte de Luengoni , brackish lake at cave entrance, coll. G. Boxshall and J. Daume, 22 October 2000 (largest female parasitised by hemiarthrine bopyrid).

Description. See Whitelegge (1897); Coutière (1899); Banner & Banner (1960); Hayashi (1996).

Colour pattern. Pinkish to bright red or red-orange, depending on the state of contraction of numerous red chromatophores, organised in more or less diffused bands on the abdomen ( Fig. 11 A).

Size range. The specimens from Minami Daito (female) and Christmas Island (male) are comparable at cl 5.8 mm, tl 16.9 mm and cl 5.0 mm, tl 13.6 mm, respectively; specimens from Sulawesi ranged from cl 5.50 mm to cl 7.00 mm; the largest syntype specimen from Funafuti had a tl of 14 mm ( Holthuis 1963); Banner’s (1957) specimen from Jaluit is one of the largest known at tl 17 mm; specimens from Fakaofo ( Holthuis 1963) and Rapa Nui ( Saavedra et al. 1996) were somewhat smaller, at tl 9–12 mm and tl 11–12 mm, respectively.

Ecology. Land-locked anchialine pools, anchialine caves, crevicular brackish pools in mangrove swamps etc.; for detailed ecological and biological notes see Banner & Banner (1960), Holthuis (1963), and summary in Anker (2009).

Type locality. Funafuti Atoll, Tuvalu.

Distribution. Indo-West Pacific: Tuvalu: Funafuti Atoll ( Whitelegge 1897); Tokelau: Fakaofo ( Holthuis 1963); Kiribati, Marshall Islands: Jaluit and Arno Atolls (Banner 1957; Banner & Banner 1960; Gressitt 1961); Rapa Nui ( Saavedra et al. 1996); Japan, Ryukyu Islands: Minami Daito and Miyako Islands ( Miya 1996; Hayashi 1996; Komai & Fujita 2005); Loyalty Islands: Lifou (Anker 2001, 2009; present study); Indonesia, Sulawesi: Muna; Christmas Island (present study) ( Fig. 12 ).

Remarks. The frontal margin of the carapace of M. minutus appears to be somewhat variable. For instance, in the Minami Daito specimen, the orbital teeth are very small and strongly directed mesially, while the rostrum is almost as long as broad at base ( Fig. 8 A). In the Christmas Island specimen, the orbital teeth are longer and more forwardly directed, while the rostrum is more elongate, clearly longer than broad at base ( Fig. 9 A). Similarly, the third and fourth pereiopods are stouter in the Minami Daito specimen (approximately 7 times as long as broad, cf. Fig. 8 D) than in the Christmas Island specimen (approximately 10 times as long as wide, cf. Fig. 9 F). With only one specimen from each Minami Daito and Christmas Island, and four specimens from Lifou, it is difficult to explain the above-mentioned morphological differences; examination of larger specimen series from different localities, if possible combined with DNA analyses, will be necessary to address this issue.

Figures

FIGURE 8. Metabetaeus minutus (Whitelegge, 1897), female from Minami Daito Jima (FLMNH Arthropoda UF 23251): A, frontal margin of carapace, dorsal; B, third maxilliped, lateral; C, second pereiopod, lateral; D, third pereiopod, lateral; E, fifth pereiopod, propdus and dactylus, lateral; F, uropod, dorsal; G, same, tooth on distolateral margin of endopod.

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 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).