Mollusca

These soft-bodied, legless animals usually secrete calcium carbonate shells. They include clams, oysters, snails, chitons, squid and octopuses. There are 85,000-110,000 species found worldwide, the largest group of animals in the sea.

There are four major classes: Gastropodea (snails and slugs), Bivalvia (bivalves, clams and oysters), Cephalopodea ( squid and octopuses) and Polyplacophora (chitons). Ninety-five percent of all these species are found in Gastropodea or Bivalvia.

They all have unique characteristics. They have a muscular foot, a fleshy mantle around the body that secretes the shell and a chitinous radula - a rasping, tongue-like feeding organ containing tiny teeth.

They reproduce by releasing eggs and sperm into the water column or laying them on a substrate. The fertilized eggs hatch into trochophore larvae and later develop into tiny, shelled larvae, veligers, which will drift with the plankton until they settle down on a suitable substrate to mature into adulthood.

Class Gastropodia

This is the largest molluscan class at 30,000 species, about one-half of which are marine. They have a distinct head with a mouth, rasping tongues (radula) and sensory organs.

They move, dig or swim using the broad foot. Many have no shells.

These animals are classified by the location of their gills. Prosobranchs have forward gills, located over the head under the mantle. These are the marine snails. Opisthobranchs have gills that are placed behind the head. These animals are the marine slugs.

Subclass Prosobranchia

These sea snails or spiral shells secrete a single hard shell structure. This shell protects its soft body and allows space for unlimited growth. Crustacean shells always need replacement (molting) to allow for growth. These shells never do. They are shells with a single opening capable of being sealed by the withdrawing animals operculum, or by holding fast to the substrate.

These creatures have to eat, breath and excrete at the same end. This is the disadvantage of a shell with only a single opening. To solve this problem, their bodies underwent torsion, a twisting of 180 ° which places the gills and anus near the foot, and the mouth forward of them. This is a characteristic of all marine snails.

Family Cypraeidae

These are the cowries. They have shining globular shells with an outer whorl that wraps around and envelops the inner whorl. This hides the shells' spiral structure. Their mantle often extends over the whole outer surface, keeping the shell glossy and smooth.

These animals are usually found in shallow, tropical waters in rocky or coral areas, often in breeding pairs. Most are nocturnal and found hidden in nooks and crannies during the day. Many are herbivorous, but some prey on sponges and other sessile animals.

Tiger Cowry
(Cypraea tigris)

The largest tiger cowries in the world are found in Hawaii - up to 6". Over-collecting has made these sizes rare, The ones found today are still too large to hide effectively. This is probably why they are more likely to be seen than any other. There are often found as shallow as ten feet.

The shells have a simple pattern of white with differing numbers and sizes of light and dark spots. Each individual animal is said to have its own unique pattern. The Tiger Cowry's mantle is covered with soft, branching fingers called papillae, long, pointed and tipped in white.

Family Ranellidae

These brightly colored triton shells are usually thick, solid, and heavily sculptured with rib-like nodules. The inner lip of the opening is usually toothed. They feed on echinoderms and molluscs that they subdue with acid secretions.

Triton's Trumpet
(Charonia tritonis)

This is the giant triton shell that can reach a length of 20", the second largest in the Indo-Pacific area. It feeds on sea stars and urchins, including the Cushion Star, the Crown-of-Thorns Star and the Red Pencil Urchin.

The shell itself is relatively smooth, with spiraling ribs and low veins often obscured by the presence of coralline algae. It has a large, red-orange aperture and an inner edge, a columella, striped with dark brown and white. You may notice that this Triton has had its point broken off. This was probably done deliberately to prevent a collector from taking it. They won't take an imperfect specimen. It does the Triton no harm.

To continue to the Opisthobranchs