Re: RE: shells and rocks

Hi Christina,

Thanks for your questions. I'll answer them one at a time..

> what different types of shells are there?

There are thousands upon thousands of species of snails that make shells. In the biological heirarchy of things, snails belong to a group called Mollusca, and are referred to as molluscs in scientific terms. Within this grouping are six major subgroups that further define different 'kinds' of snails:

1. Bivalves: These are snails that create two shells for their home. Examples include oysters, clams and scallops.
2. Monovalves or Gastropods: These snails create a single shell, most often with a spiral shape. The term gastropod refers to the fact that these snails move by walking on a muscular foot which happens to contain most of their vital organs (gastro = stomach; pod = foot). Members include conchs, whelks and cones.
3. Tusk Shells or Scaphopods: The shells from these snails are not siral, but look like an elephant tusk. The animals lives within the shell and has a strong foot that sticks out of the wider end of the 'tusk.'
4. Chitons: Chitons looks rather like armored caterpillars. They have eight overlapping plates on top and a very strong muscular foot underneath. You can find them living on rocks and other solid surfaces where they eat algae that adheres to the same surface.
5. Cephalopods: As with 'gastropods' -- cephalo = head and pod = foot. Cephalopods thus appear to have their arms coming directly out of their head. Members include the squid, octopus and the chambered nautilius. Among the invertebrates (animals lacking a vertebrate column, or spine) they are the most intelligent.
6. Gastroverms: This group is the most primitive and evolutionarily anicient group of molluscs. They are very rare and generally found only at great depths.

> what different types of rocks are there?

Rocks fall under three main categories:
igneous: volcanic rocks that form from mamga expelled from the earth's interior.
sedimentary: these rocks form after millions of years of pressure compresses sediments in swamps or on the ocean bottom. Shale is an example of a sedimentary rock.
Comglomerate: Mixture of different kinds of rock.

> what jobs can people have using shells?

Many marine biologists specifically study snails. People who study snails are referred to as malacologists.

> what is the history of shells?

The first primitive molluscs appeared a little before the Cambrian period, roughly 500 million years ago! The 500 million years of evolution has lead to the rich diversity of snails found in the six classes listed above. The Internet Resource Guide for Malacologists and Conch-Net can provide you with links to more sites concerning snails and shells.

-Lynn Bry