The depth of water plays a crucial role in the habitat of mollusks. For the depth affects the temperature and plant life, both crucial for survival. Most mollusks can only survive in certain depth habitats, while others are may move about freely. The following are the major habitat classifications by depth.
Fresh Water - (non-salt water bodies)
This world includes rivers and lakes and just about any other body of water that does not include salt water. They can usually be found by digging in muddy or sandy bottoms.
Terrestrial - (land based)
These are the creatures you may find in your own backyard. Many live in trees, some live in the ground or in stone walls or cliffs. They can usually be found in damp areas such as under moss, logs, fallen leaves. They are more commonly seen after rain, when the humidity entices them to leave their hiding places.
Pelagic – (near the surface of the ocean)
About 100 species live in this area. Some float, some are attached to weed, while still others hover in mid-water.
Littorial -
The littorial world includes millions of miles of inter-tidal shoreline and shallow water depths. This habitat extends down as far as algae can survive. This is the farthest depth at which plants that utilize photosynthesis extends. Since this boundary depends on the transparency of the water, an exact depth cannot be assigned to measure it. The Littorial world is divided into four planes:
Supralittorial Plane – (the strip of beach above the high-tide level) Only submerged occasionally, it is the transitional environment between water and land, which the sea can only keep moist through spray from a combination of wave and wind.
Mesolittoral Plane – (from the high-tide mark to the low-tide mark) Also know as the inter-tidal zone, the sea periodically submerges this area.
Infralittoral Plane – (from the low-tide mark to shallow depths) Also known as the shallow water world, this area includes most coral reef systems. This plane is actually measured down to a depth where a certain type of plant called the Zosteraceae can survive. It is an area easily accessible by man.
Circumlittoral Plane – (Down to lowest depth at which green algae can survive) Sitting on the edge of the continental shelf, one of its characteristics is the calcareous remains of both animals and plants.
Abyssal – (From the point where plants can survive down to the depths of the sea) This world contains small, mainly colorless shells that live in the lightless depths of the sea where temperatures near freezing. Abyssal species are similar in all parts of the world. Deep-sea mollusks living near the equator are also found in shallow waters in the polar seas. Both clams and gastropods have been found three miles down.
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