Opinions and declarations Rendered by the International Commission on Zoological Nomenclature

This is probably the first record of an Amphidromus species utilizing an invasive, non-native tree species of the genus Acacia as a habitat. This observation is interesting considering that the tree species Acacia mangium is a recent introduction from Australasia with not more than 30 years of presence in Southeast Asia (Osunkoya et al., 2005, Krishnapillay et al., 2007). Sutcharit et al. (2013) suggested that Amphidromus species may be less restrictive in their selection of tree species as habitat than historically thought. Some Amphidromus species have been reported to make egg nests with the leaves of bamboo (family Poaceae, tribe Bambuseae) (Paravicini, 1921), mango Mangifera indica (Paravicini, 1921; Sutcharit et al., 2013), pomelo Citrus grandis (Sutcharit & Panha, 2006), rambutan Nephelium lappaceum (Sutcharit & Panha, 2006), banyan Ficus microcarpa (Sutcharit & Panha, 2006) and jackfruit Artocarpus spp. (Paravicini, 1921; Sutcharit et al., 2013). The authors have also observed A. atricallosus perakensis on banana Musa sp. and cocoa Theobroma cacao foliage in Malaysia. Amphidromus have also been found on concrete structures near vegetated areas (Lok & Tan 2008; Sutcharit et al., 2013). The diverse range of trees and structures used by Amphidromus for shelter and egg-nesting suggests that macrohabitat may not be the sole driver of survivability for Amphidromus species. Rather, the presence of Amphidromus may be more determined by the availability of moist microhabitats created by various species of leafy trees and the abundance of microfloral food sources (Lok & Tan, 2008; Sutcharit et al., 2013). This runs contrary to other arboreal snail taxa such as those from Moorea and Hawaii, which rely on particular tree species for habitat (Murray et al., 1982, Meyer et al. 2014). Overall, this incidental observation lends support to suggestions that Amphidromus species are adaptable to well-vegetated anthropogenic areas. However, further research is needed to identify if Amphidromus populations could persist in anthropogenic habitats over the longer term. In particular, investigations should be made on whether Amphidromus atricallosus perakensis could establish successful nesting on non-native species such as Acacia mangium. It should be noted that Amphidromus atricallosus perakensis is thought to be a non-native species in Singapore (see Tan & Chan, 2011).

Overall, this incidental observation lends support to suggestions that Amphidromus species are adaptable to well-vegetated anthropogenic areas. However, further research is needed to identify if Amphidromus populations could persist in anthropogenic habitats over the longer term. In particular, investigations should be made on whether Amphidromus atricallosus perakensis could establish successful nesting on non-native species such as Acacia mangium.

In Singapore, this arboreal snail is also known from Seletar, Mandai, Nee Soon Swamp-forest, and Bukit Timah Nature Reserve, as well as the islands of Tekong and Ubin (Tan et al., 2011; Tan & Xu, 2013). This appears to be the first record from Chestnut forest. Apart from the population at Nee Soon, it seems to be the only other population with a mix of sinistral and dextral individuals (Tan Siong Kiat, personal communication.)

The shell characteristics and soft body colouration of the animal agrees with Amphidromus atricallosus temasek, but is unusual in having a white shell. Conspecifics on Singapore Island have green shells in life, and empty shells are yellow. This is the first published record of Amphidromus atricallosus temasek from Pulau Ubin. Elsewhere in Singapore, this taxon occurs in the Central Nature Reserves and on Pulau Tekong (Tan et al., 2011).

However, as the relevant reference literature is not readily accessible, it is not possible to identify the taxa

Most Hemiplecta humphreysiana individuals were observed to live under and among fallen logs and leaf litter on the forest floor at the same location. Historical reports of the species have not noted any tree-climbing behavior (Ho, 1990 and references therein). The only other record of semi-arboreal behavior for the genus Hemiplecta is from Hemiplecta cymatium, which has been noticed primarily on trees and occasionally on the ground (Stoliczka, 1973). We believe this observation of arboreal behaviour in H. humphreysiana has not been published. From our personal observations prior to this, H. humphreysiana individuals have been seen at a maximum height of around 2 m on man-made structures in the Nee Soon Swamp Forest Ho (1990) commented that Hemiplecta humphreysiana can be found on algae-covered logs. This species has also been observed to graze on fungi (Mableinsingapore, 2007; Artistscaravan, 2011a, 2011b; Tan et al., 2012). We speculate that the impetus for the snail’s semi-arboreal behavior could be due to the high humidity brought by monsoonal rains as well as the availability of algae and fungi on the normally drier tree surfaces. However, further studies are required to gauge the propensity and nature of such behavior. If quantitatively validated, this behavior may be considered a niche extension for H. humphreysiana and hence, may have ecological and evolutionary implications such as predation exposure and character displacement (Chiba, 1996).