Marine Ancestors of most Land Snails: Pulmonates

Abstract

Marine pulmonates (Pulmonata) can aquire oxygen from open air; they are hermaphrodites. Siphonaria, of intertidal rocky shores, breathes by gill when tides rise, by lung when tides recede; copulation is mutual or one-sided, eggs are laid in capsules from which veligers hatch; in some, embryonic development occurs within the capsule and crawling juveniles emerge. Gadinalea, of mid-tidal caves, produces a mucus curtain in which plankton is trapped. Amphibola, a detritus-feeder of mud flats high up the shore, breathes both aerial and aquatic oxygen; it can cope with freshwater for considerable periods. Onchidiidae are air-breathing sea (and land) slugs of intertidal rocky coasts which feed during low tide; some live in rainforests. Myosotella, of salt marshes, breathes only through a lung and drowns if kept underwater; eggs are deposited in capsules, in which veligers develop and metamorphose, eventually hatching as crawling juveniles. Carychium, a primitive air-breathing pulmonate of damp river bank litter, lays eggs which develop directly to a miniature adult. Advanced pulmonate land snails lay enormous eggs with much yolk and water, enabling complete development of the embryo within the egg and hatching as a crawling juvenile; each egg may be 50,000 times larger than that of a sea snail.