Evidence that reduction of the apertural closing apparatus has no decisive effect on water loss in the land snail family Clausiliidae (Gastropoda: Stylommatophora)

Abstract

Abstract Apertural barriers of land snails are thought to increase their shell’s effectiveness against dehydration and predation. The most complex apertural barrier among stylommatophoran snails is the clausiliar apparatus (CA) of Clausiliidae. Alopia is a unique genus in having a remarkably high proportion of taxa with a naturally reduced CA, representing at least five independent reduction events. We tested the prevailing hypothesis that the primary role of the CA within the door snail family is to help retain body moisture. In a laboratory experiment, we compared the water loss of two Alopia taxa with naturally reduced and two Alopia taxa with complete CAs. There was a detectable difference in the rate of water loss, but no relationship with the presence/absence of the CA could be shown. In another laboratory experiment, this time in Alinda biplicata, we did not detect significantly higher water loss in specimens from which the clausiliar plate was artificially removed compared to those left intact. These results suggest that the CA has no significant role in water retention but its actual function remains speculative. A possible explanation, which requires further work, could be that the CA provides protection against specific predators intruding through the aperture.