The
phylum Mollusca is made up of six classes consisting of 50,000 living
species and 35,000 described fossil species. The four classes of molluscs
found in Puget Sound are: Bivalvia (clams, oysters, mussels, ect.), Gastropoda
(snails, limpets and nudibranchs), Polyplacophora (chitons) and Cephalopoda
(octopus and squid). Most molluscs have three body regions consisting
of a head, a visceral mass surrounded by the body wall, and a foot. The
head includes the brain, sense organs and a mouth. The visceral mass,
or body cavity, is reduced. It is restricted to certain organ cavities,
such as the excretory organs, the pericardium, and the gonads. The mantle
cavity, containing the gills, excretory pores and the anus, is found between
the visceral mass and the mantle which secretes the shell. The foot of
molluscs is a strong muscle that allows them to creep along the substrate,
the surface that the animal lives on. Two different types of feeding occur
in Molluscs: filter feeding, herbivorous or carnivorous predation and
deposit feeding (e.g. Macoma). In filter feeding, water is drawn into
the mantle cavity by ciliary action. Food particles suspended in the water
become trapped in mucus as they pass over the gills and are then moved
to the mouth along the ciliary pathways. Predatory feeding occurs with
the use of jaws and a radula, although cephalopods use a beak to kill
and tear apart their prey. Herbivores use a radula to scrape plant matter
off of the substratum, where carnivores use muscular jaws to hold prey
while the radula rasps off pieces of the prey to ingest. All molluscs
reproduce sexually and can be either hermaphroditic or have separate sexes.
The
phylum Mollusca is made up of six classes consisting of 50,000 living
species and 35,000 described fossil species. The four classes of molluscs
found in Puget Sound are: Bivalvia (clams, oysters, mussels, ect.), Gastropoda
(snails, limpets and nudibranchs), Polyplacophora (chitons) and Cephalopoda
(octopus and squid). Most molluscs have three body regions consisting
of a head, a visceral mass surrounded by the body wall, and a foot. The
head includes the brain, sense organs and a mouth. The visceral mass,
or body cavity, is reduced. It is restricted to certain organ cavities,
such as the excretory organs, the pericardium, and the gonads. The mantle
cavity, containing the gills, excretory pores and the anus, is found between
the visceral mass and the mantle which secretes the shell. The foot of
molluscs is a strong muscle that allows them to creep along the substrate,
the surface that the animal lives on. Two different types of feeding occur
in Molluscs: filter feeding, herbivorous or carnivorous predation and
deposit feeding (e.g. Macoma). In filter feeding, water is drawn into
the mantle cavity by ciliary action. Food particles suspended in the water
become trapped in mucus as they pass over the gills and are then moved
to the mouth along the ciliary pathways. Predatory feeding occurs with
the use of jaws and a radula, although cephalopods use a beak to kill
and tear apart their prey. Herbivores use a radula to scrape plant matter
off of the substratum, where carnivores use muscular jaws to hold prey
while the radula rasps off pieces of the prey to ingest. All molluscs
reproduce sexually and can be either hermaphroditic or have separate sexes.