Mollusca
Bivalvia
- Includes clams, oysters, mussels, scallops and numerous other families of shells.
- Most bivalves stay in the same place for much of their lives, but others are able to move around. Burrowers move up and down through mud and sand by extending their foot. Then they expand the tip of their foot to anchor themselves and pull their shelled bodies up or down in the burrow. Others "swim" through the water by clapping their valves together.
-Bivalves usually require both males and females to reproduce, although some species individuals either have the organs of both sexes or start out as males and later become females. Bivalve eggs and sperm are usually released into the water, where fertilization takes place. The eggs hatch into veligers that live among and eat other plankton. Plankton is made up of microscopic plants and animals that drift about on ocean currents. Eventually, the veligers settle on rocks, wood, or the ocean bottom and begin to develop their valves.
- Most bivalves stay in the same place for much of their lives, but others are able to move around. Burrowers move up and down through mud and sand by extending their foot. Then they expand the tip of their foot to anchor themselves and pull their shelled bodies up or down in the burrow. Others "swim" through the water by clapping their valves together.
-Bivalves usually require both males and females to reproduce, although some species individuals either have the organs of both sexes or start out as males and later become females. Bivalve eggs and sperm are usually released into the water, where fertilization takes place. The eggs hatch into veligers that live among and eat other plankton. Plankton is made up of microscopic plants and animals that drift about on ocean currents. Eventually, the veligers settle on rocks, wood, or the ocean bottom and begin to develop their valves.
Gastropoda
- The Class Gastropoda includes snails, slugs, limpets and sea hares. All of these animals are referred to as 'gastropods.' Gastropods are mollusks, an a extremely diverse group that includes over 40,000 species.
-Some gastropods are dual sexed. One interesting animal is the slipper shell, which may start out as a male and then change to a female. Depending on the species, gastropods may reproduce by releasing gametes into the water, or by transferring the male's sperm into the female, who uses it to fertilize her eggs. Once eggs hatch, the gastropod is usually a planktonic larvae called a veliger, which may feed on plankton or not feed at all. Eventually, the veliger undergoes metamorphosis and forms a juvenile gastropod.
-Some gastropods are dual sexed. One interesting animal is the slipper shell, which may start out as a male and then change to a female. Depending on the species, gastropods may reproduce by releasing gametes into the water, or by transferring the male's sperm into the female, who uses it to fertilize her eggs. Once eggs hatch, the gastropod is usually a planktonic larvae called a veliger, which may feed on plankton or not feed at all. Eventually, the veliger undergoes metamorphosis and forms a juvenile gastropod.
Cephalopod
- Cephalopods are the most intelligent, most mobile, and the largest of all molluscs. They include Squid, octopuses, cuttlefish, the chambered nautilus, and various other large bodied mollusca.
- Sex and reproduction in cephalopods is in many ways quite different than in other molluscs. First, sexes are separate and mating usually includes a courtship that often involves elaborate color changes. This is followed by the transfer of a spermatophore by a male to a female through her mantle opening. The spermatophore is transferred by the male using either a penis or a modified arm called a hectocotylus. Most females then lay large yolky eggs in clusters on the ocean floor or on any other hard substrate. Eggs develop by dividing unequally instead of in the spiral pattern of other molluscs. It is thought this is a derived mode of development. After a period of development within the egg, juveniles hatch out directly without the swimming larval stage common to many other molluscs. Most males and females die shortly after spawning.