Under the sea

Micromollusk This is a micromollusk, a tiny seashell. It is about 1.2 mm long. Mollusks are soft-bodied invertebrates, usually with a hard external shell or, sometimes, an internal one, at least at some time in their life cycle. Seashells are gastropods, which includes snails and slugs. The smallest gastropods, like this one, are barely visible, whereas the California black sea hare weighs as much as 14 kg (30 lb)! Gastropods can be found in both marine and freshwater habitats. The ancestors of gastropods had right and left sides, but they evolved to become asymmetric. This happened through two processes, the first of which was torsion, a twisting of the body with rearrangement of some of the organs, probably to protect the head. The second process was the development of a coiled shell in some species. The snail can usually crawl around easily, but can also withdraw into its shell and close the opening with an operculum (like a trap door) on its foot. Original image courtesy of Dr. Carole Hickman, University of California, Berkeley.

 

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