VCSU Macro-Invertabrate Lab

Phylum Mollusca - The Mussels and Snails

The mollusks are composed of two large groups, the gastropods (snails) and bivalves (mussels or clams). The mollusks are recognized by their hard shells surrounding soft bodies. Snails generally live near shore in many water bodies where they eat detritus and algae. Mussels filter organic material from water and generally live partially buried in the sediment.

General Life cycle - Snails emerge from eggs laid in gelatinous groups. Most freshwater snails live about a year, some live up to four years. Some are hermaphrodites that can fertilize themselves. Other groups have separate sexes. Mussels may also be hermaphroditic and self-fertilize. Many develop inside the adult for a period of time and emerge looking like small clams. However instead of starting life as filter feeders they usually parasitize on fish for a few weeks. Then as juveniles they live in the sediment for up to eight years before maturing sexually. Total lifespan may reach 15 years.

Identification - Members of Gastropoda have a single shell which is often coiled. The soft body includes a head, foot, and visceral mass. Members of Bivalvia have a shell in two parts connected by a hinge. Bivalves do not have heads.

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