Thank you very much.  I only saw a change in whorl expansion rate but couldn't see a clear boundary. I'm curious if its only the marine taxa that show a morphological change (in ornamentation) during the transition from Proto to Teloconch and not the freshwater snails.

I found in all species studied a clear boundary delimiting the shell of the pre-hatching and posthatching animal, in land and water snails. Often there is a change in ornament and hatching is usually indicated by increments of growth. In cases of shell structure I noticed no difference, but it may be retarded.  In  case of brood pouch development matters may be more complicated. This sis quite well known in case of Melanoides tuberculata. Special features also characterize limpets such as Ancylus of Acroloxus.

As Klaus says, in many/most freshwater snails there is a clear boundary that marks hatching - but it may examination under SEM to see it clearly. However, the presence of this change in growth lines/ornament/ whorl inflation etc. may be dependent on whether the young animals are brooded or not. In some snails that brood there is no indication in the shell of the point in time when the young snail was released into the water from the mother's brood pouch.

Dear Ranjeev,

In addition to what Jon and Klaus already wrote the protoconch/teleoconch distinction depends a little on the group of snails you're looking at. Some families, like the Planorbidae, show a quite clear distinction, while in others (some Lymnaeidae or Melanopsidae) there is little or no differentiation in ornamentation and rarely a clear boundary (at least in the species I examined). As Jon said, this depends a lot on the mode of reproduction, which differs greatly among freshwater Gastropoda (see e.g. Dillon, R.T. 2004. The Ecology of Freshwater Molluscs. Cambridge University Press; parts of the book are free on Google Books).

Cheers, Thomas

Thank you very much Dr. Bandel, Dr. Todd and Dr. Neubauer,. I will try taking some SEM's and re-examine them again.