Alainodaeus Davie, 1993

Mendoza, Jose Christopher E. & Ng, Peter K. L., 2008, A new species of Alainodaeus Davie, 1993 (Crustacea: Decapoda: Brachyura: Xanthidae) from Balicasag Island, Philippines, with a key to the genus, Zootaxa 1897, pp. 53-63 : 54-55

Alainodaeus Davie, 1993

Type Species. Alainodaeus akiaki Davie, 1993 , by original designation. Gender masculine.

Remarks. Davie (1992) discussed the affinity of Alainodaeus with Medaeops and Monodaeus . Davie (1997) subsequently noted similarities in the form of the carapace, particularly between A. nuku and another xanthid genus, Nanocassiope Guinot, 1967 , as well as other panopeid genera such as Micropanope Stimpson, 1871 , Coralliope Guinot, 1967 , and Gonopanope Guinot, 1967 . He also commented that the forms of the G1 of Nanocassiope , Coralliope and Gonopanope were too different from the general form in Alainodaeus , although he notes that Micropanope has “a relatively simpler G1, not unlike that of Alainodaeus ” ( Davie 1997: 347).

Two additional features appear to link Alainodaeus more closely to Euxanthinae . The presence of welldeveloped endostomial ridges in Alainodaeus (Fig. 3A) is a feature shared with other euxanthine genera such as Cranaothus Ng, 1993 , Epistocavea Davie, 1993 , and Ladomedaeus Števčić, 2005 (cf. Davie 1993; Ng 1993; Manuel-Santos & Ng 2007). The form of the G 1 in Alainodaeus (e.g., Figs. 4E, F) is most similar to that seen in other euxanthine genera such as Crosnierius Serène & Vadon, 1981 , and Ladomedaeus . This is especially so for species such as A. akiaki , A. rimatara and A. filipinus n. sp. The G 1 in these crabs is moderate in length, a little more than twice the length of the G2, outwardly and laterally curving, spinulose on the distal half, without any terminal or subterminal setation and, instead, having a distinct lobe or “tongue” at its distal tip ( Serène & Vadon 1981; Davie 1993, 1997; Ng & Chen 2005; Manuel-Santos & Ng 2007). The “flange” or crest on the lateral margin noted by Davie (1992, 1997), a feature shared with some species of Medaeops and Monodaeus , is also found in Crosnierius and Ladomedaeus .

A few works have cited the occurrence of a strongly differentiated, obliquely oriented tooth on the proximal end of the dactylus of the major chela (see Fig. 3C) in some species of Euxanthinae , and have alluded to the possibility of some phylogenetic significance in such a structure ( Davie 1993, 1997; Ng 1993; Ng & Clark 2003; Ng et al. 2008). This specially modified tooth is somewhat similar in structure to the shell-peeling tooth in species of Calappa Weber, 1795 , and has been thought to serve a similar purpose. The modified tooth of Calappa is used to peel off the shell of gastropods, exposing the flesh on which they feed (see Ng & Tan 1984, 1985). Although there have been no reports of such behaviour in any euxanthine crab thus far, the modified tooth has been noted in genera such as Alainodaeus , Cranaothus , Crosnierius , Danielea Ng & Clark, 2003 , Epistocavea , Medaeops , Medaeus , Miersiella Guinot, 1967 , Monodaeus , Palatigum Davie, 1997 , Paramedaeus , Paraxanthodes and Pleurocolpus Crosnier, 1995 . Other euxanthine genera such as Euxanthus Dana, 1851 , Hypocolpus Rathbun, 1897 , Hepatoporus Serène, 1984 , Glyptoxanthus A. Milne-Edwards, 1879 , and their close relatives do not possess such a tooth. However, this is a character also present in many genera in at least one other xanthid subfamily—Xanthinae, e.g. Xanthias Rathbun, 1897 , Nanocassiope , Euryxanthops Garth & Kim, 1983 , Paraxanthias Odhner, 1925 (see Ng et al. 2008). In addition, Ng & Tan (1985) also noted that the peeling tooth is also present in some eriphioids.

Prior to the discovery of the new species ( A. filipinus ), the westernmost extent of the genus Alainodaeus was in the Chesterfield Islands in the Coral Sea, between the eastern coast of Australia and the main island of New Caledonia, as represented by A. rimatara . Its northernmost extent was in the Marquesas Islands, in the central Pacific, less than 10 degrees south of the Equator, as represented by A. nuku . The ocurrence of Alainodaeus filipinus n. sp. in the central Philippines has extended the range of the genus northward to about 10 degrees beyond the Equator and westward, beyond Australia and Oceania, into Asia. In a similar extension of range, the monotypic genus Epistocavea Davie, 1993 , originally described from the Tuamotu Archipelago, was reported by Mendoza & Ng (in press) from the Bohol Sea, in the central Philippines. Another similar distributional pattern is seen in Cranaothus deforgesi Ng, 1993 , originally from the Chesterfield Islands in the Coral Sea and Philippines; and in the goneplacoid crab, Vultocinus anfractus Ng & Manuel-Santos, 2007 , which occurs both in the central Philippines and northern Vanuatu (see Ng 1993; Ng & Manuel-Santos 2007).