The feeding mechanism and ecology of the New Zealand pulmonate limpet, Gadinalea nivea



Gadinalea nivea is a marine pulmonate classed near the Siphonariidae. It lives at mid-tidal level under ledges and in small concavities, away from light, on rocky shores exposed to heavy surge, or in caves with high water turbulence. Gadinalea does not normally move about, but lives in closely aggregated colonies. In the absence of light, algal food is scarce and the animal does not in the normal way abrade the substratum with the radula.

The feeding mechanism involves the utilization of the turbulence of the water, and the animal orients very accurately to the current. In its normal position it hangs upside-down, and lowers the shell, so that the water current enters behind. Lavish mucus is produced from glands of the mantle edge and the sides of the foot. A mucous curtain is so secreted, in front of the head, extending outwards from the mantle margin and ballooning out with the current from behind. Particles of phytoplankton are in this way trapped until the mucous curtain is fully loaded. At close intervals it is inspected by the extended oral lobes, and is then enclosed by a hood formed by these lobes, and ingested.

There are no ciliary tracts involved in food-collecting, and normal feeding is not elicited in still water. Animals must be observed under suitable conditions of turbulence for feeding behaviour to appear. Measurements with a “Celloscope” cell counter showed progressive reduction of the particle content of suspensions in which Gadinalea was being fed.

The histology of the mantle edge shows highly specialized mucus-secreting tracts. The structure of the alimentary canal has a basic resemblance to that of the Siphonariidae, but in several features, especially the reduction in size of the radula teeth, has become adapted for current-borne particle feeding.