Genus Geosesarma De Man, 1892 Type species Sesarma (Geosesarma) nodulifera De Man, 1892, subsequent designation by Serène and Soh (1970). Gender neuter. Remarks De Man (1892) established Geosesarma as a subgenus of Sesarma for small-sized species that carry a small number of large eggs (De Man 1892, p. 341). He mentioned the possession of large eggs for Se. (G.) nodulifera De Man, 1892 and two undescribed species, but not for Se. (G.) sylvicola De Man, 1892. One of the two unidentified species was later described as Sesarma nodulifera var. conferta Ortmann, 1894 (now also placed in Geosesarma) (Ng et al. 2015b). Geosesarma currently contains 56 species (Ng et al. 2008a, 2015b; Naruse and Jaafar 2009; Schubart and Ng 2014; Ng 2015), and many of them are known to produce a small number of large eggs and to practise direct development (e.g. Soh 1969; Ng and Tan 1995). There are, however, some species that have a large number of small eggs [e.g. G. angustifrons (A. Milne-Edwards 1869), G. hednon Ng, Liu and Schubart, 2004 and G. maculatum (De Man, 1892) (Cai and Ng 2001; Schubart and Ng 2014)]. Serène and Soh (1970, p. 403) also indicated the heterogeneous nature of the genus and questioned the generic position of G. angustifrons (see Remarks on Sc. gracilipes). This issue is also noted in Paulay and Starmer (2011). Ng (1988) recognised three informal species groups within the Geosesarma of Peninsular Malaysia, but there are clearly other groups in the genus (e.g. Manuel-Santos et al. 2016). In addition, many Geosesarma species have never been studied or only poorly studied since their original descriptions, and access to their type material is not always easy, which makes it difficult to revise the genus. The two species here transferred from Labuanium s.l. to Geosesarma are examples of such poorly known species.

Published as part of Naruse, Tohru & Ng, Peter K. L., 2020, Revision of the sesarmid crab genera Labuanium Serène and Soh, 1970, Scandarma Schubart, Liu and Cuesta, 2003 and Namlacium Serène and Soh, 1970 (Crustacea: Decapoda: Brachyura: Sesarmidae), with descriptions of four new genera and two new species, pp. 445-532 in Journal of Natural History (J. Nat. Hist.) (J. Nat. Hist.) 54 (7 - 8) on page 509, DOI: 10.1080/00222933.2020.1763491, http://zenodo.org/record/4609148