Discovery

What I want to know is...

do baby snails have shells?

Mike Keys, Salisbury School

All baby snails have shells before they hatch, forming their shells while still inside the egg capsule, says Frank Climo of the Natural History Unit of the Museum of New Zealand. In some cases, the shell forms before the egg is even laid; in others, the shelled body forms after.

Adding potential confusion is the fact that some snail eggs are themselves shelly, looking something like a small bird's egg. Rhytidid snails and Flax snails, both found in New Zealand, lay shelled eggs. The eggs of the latter are six-millimetre ovals, laid in batches of 20-30, with several flax snails contributing to the shallowly buried nest.

Some small snails in New Zealand get lime to build their shells before they hatch by drawing it through the walls of the soft outer layer membrane of the egg capsule. They do this by dissolving and absorbing lime from empty shells in the surrounding leaf litter.

There are snails which brood encapsulated embryos in the whorl-spiral cavity -- the umbilicus -- on the underside of the parent. These embryos absorb the lime from the parental shell, causing characteristic etching on the shell similar to the scavenged empty shells of their non-parented counterparts.

Climo is keen to see biochemists and behaviouralists undertake further investigation of this "etching-through-membrane" phenomenon.

Scanning electron microphotographs courtesy of the Victoria University EM Facility.

Mike Keys teaches at Salisbury School.