Holthuisana Bott, 1969

Wowor, Daisy & Ng, Peter K. L., 2009, Two new species of Holthuisana Bott, 1969 (Crustacea: Decapoda: Brachyura: Gecarcinucidae) from West Papua, Indonesia, Zootaxa 2071 (1), pp. 50-60 : 51-52

Holthuisana Bott, 1969

Remarks. In a paper on new genera of freshwater crabs, Bott (1969) established a new genus, Holthuisana , with two subgenera, Holthuisana (Holthuisana) Bott, 1969 (from New Guinea), and Holthuisana (Austrothelphusa) Bott, 1969 (from Australia). In his revision of the New Guinean freshwater crabs, Bott (1974) recognised five species of Holthuisana (Holthuisana) : H. (H.) biroi ( Nobili, 1905) , H. (H.) festiva ( Roux, 1911) (type species), H. (H.) wollastoni ( Calman, 1914) , H. (H.) subconvexa ( Roux, 1927) , and H. (H.) boesemani Bott, 1974 . Holthuis (1980) subsequently described a new cavernicolous species, Holthuisana alba , from Papua New Guinea. Holthuisana Bott, 1969 , and Austrothelphusa Bott, 1969, have since been recognised as separate genera (see Ng & Guinot 1998; Davie 2002; Ng et al. 2008).

Bott’s (1970, 1974) concept of Holthuisana poses some problems because he did not examine most of the types of the junior synonyms, did not elaborate on his reasons for his synonymy, and some of the differences between purported synonyms are so distinct that it is unlikely that they are conspecific. Despite marked differences between the anterolateral and external orbital angle armatures of Parathelphusa (Liotelphusa) briggsi Rathbun, 1926 , Potamon (Geotelphusa) beauforti Roux, 1911 , and H. biroi (cf. Nobili 1905; Rathbun 1926; Roux 1911; Bott 1970, 1974), all were regarded by Bott (1970) as belonging to one taxon. In addition, Bott (1970) synonymised Potamon (Potamonautes) loriae Nobili, 1899 (Havari, Papua New Guinea) with H. festiva with doubt, but later Bott (1974) considered the identity of Nobili's specimen to be undeterminable. Nobili (1899) did not provide figures, but he mentioned that P. loriae was very close to Sundathelphusa philippina (von Martens, 1868) from the central Philippines in carapace form (i.e. with a transverse carapace and very convex anterolateral margins) (see also Ng & Sket 1996). This character alone suggests that the affinities of P. loriae are closer to H. subconvexa rather than the flatter H. festiva , and that the two species are not synonyms. Paratelphusa (Liotelphusa) vanheurni Roux, 1927 , was synonymised with H. festiva by Bott (1970, 1974), but the marked differences in their carapace features suggest that two separate taxa are involved. Holthuisana festiva was described from Tanah Merah at the region of Lake Sentani, Papua Province, Indonesia, while H. vanheurni comes from a location well south of it. Bott (1974) later considered H. vanheurni to be a form of H. festiva . Considering the wide geographical range of H. festiva , more collections and studies are clearly needed to resolve this problem. Ng et al. (2008) opted to recognise all the above species as valid taxa but did not elaborate. The present notes, which formed the basis of Ng et al. ’s (2008) action, have been presented above. The present authors also prefer to wait until the types of these species can be directly compared before any of the names are formally synonymised.

The species of Holthuisana can also be divided into two distinct groups. The group with Holthuisana s. str. contains two species, including the type species H. festiva and H. vanheurni . It is characterized by having almost a quadrate carapace in which the dorsal surface is only slightly convex; the regions of the carapace are not distinctly inflated; the anterolateral margins are gently convex; the epibranchial tooth is prominent, very well developed and sharp and is clearly separated from the distinctly triangular external orbital angle by a deep notch; the margin of the external orbital angle is truncated and straight; the ambulatory legs are relatively stouter and shorter than in the second group; the male abdomen is broadly T-shaped with the distal somites relatively short and broad, the sixth somite having distinctly concave lateral margins and the telson triangular with concave lateral margins; and the G1 is relatively slender, the terminal segment being cone-shaped, sharptipped and demarcated (but not very clearly) from the subterminal segment, its length being subequal to or slightly shorter than half the length of the subterminal segment.

Members of the second group of Holthuisana ( H. alba , H. biroi , H. boesemani , H. loriae , H. subconvexa , H. wollastoni ) are distinct in possessing a distinctly ovate carapace, highly inflated carapace regions; prominently convex anterolateral margins; an indistinct epibranchial tooth that appears almost confluent with the external orbital angle, the margin of which is convex or straight; relatively short and slender ambulatory legs; the male abdomen is usually more distinctly T-shaped, with the distal somites usually relatively long and slender; and the G1 is relatively more slender to slightly stout, the terminal segment being stouter, more cylindrical and indistinctly separated from the subterminal segment, and approximately one third the length of the subterminal segment.

Whether the two groups of Holthuisana represent separate genera should only be determined after all the type material is examined and the genus revised. The two new species from Waigeo ( H. tikus n. sp.) and Batanta ( H. lipkei n. sp.) have highly swollen carapaces and clearly belong to the second group of Holthuisana .