Consumption of amphipods by the New Zealand land snail Wainuia urnula (Pulmonata: Rhytididae)

Abstract

An unusual carnivorous diet was documented for the rhytidid snail Wainuia urnula urnula (Pfeiffer) from the southern North Island, New Zealand. Eighty-two percent of 315 samples of faeces or gut contents contained remains of landhoppers (Crustacea: Amphipoda). Earthworms (Oligochaeta) were the second most common food type identified, but occurred in only 4 percent of samples. In the laboratory, W. urnula urnula captured landhoppers by rapidly everting the 'V'-section odontophore beneath the prey and immediately drawing it into the mouth in a single action. Diet samples from the allopatric congeners W. edwardi (Suter) (n = 51) and W. clarki Powell (n = 7) contained no remains of landhoppers, and these snails did not eat landhoppers in the laboratory. The diet of these species was dominated by earthworms. The subspecies W. u. nasuta ate both earthworms and amphipods with similar frequency (n = 40). Individual teeth on the radula of W. urnula urnula had a simple blade-like cusp like other Wainuia species, but there were fewer teeth per row and fewer rows on the whole radula than in other species. W. u. nasuta had a similar number of rows of teeth to W. clarki and W. edwardi, but the number of teeth per row was intermediate between these species and W. u. urnula. Records of pulmonate species preying on arthropods are rare, yet in the case of W. urnula this specialization has been accompanied by minimal morphological change.