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Ganl. Bull. Singapore 70 (Suppl. 1) 2018 
Fig. 15. Distribution and abundance of subclass Collembola in the Nee Soon drainage. Solid 
circles indicate sites where representatives were collected and circle sizes are proportionate to 
abundance/numbers of individuals captured as reflected in the accompanying legend. 
Order Basommatophora 
The order Basommatophora is part of a larger group called the Pulmonata, also known 
as the air breathing snails and slugs. Together with a modified mantle cavity, which 
allows them to breathe atmospheric air, the members of this order have their eyes on 
the base of their tentacles (Ruppert & Barnes, 1994). Two families from this order - 
Physidae and Planorbidae, were found in the Nee Soon drainage in large numbers, 
but only in the northeast of the Nee Soon drainage. Relatively larger numbers of 
Planorbidae (8 and 27 individuals) were recorded at sites 31 and 32, while only two 
Physidae individuals were recorded at site 32 (Fig. 16). Their absence from the rest of 
the swamp forest could possibly be due to the lower pH levels within the rest of the 
Nee Soon drainage, as snails are intolerant of acidic conditions (Zischke et al., 1983). 
