phylum mollusca (SNAILS, SLUGS, OCTOPi, SQUIDS)
• 110,000 species are known.
• Live in a vast range of habitats - both aquatic and terrestrial.
• Vary in size.
• Most mollusks are marine.
• Most have a shell.
TYPES
Gastropods - snails and slugs.
Bivalves - clams, oysters, mussels, and scallops.
Cephalopods - octopi, squids, cuttlefish, and nautili.
SYMMETRY
Bilateral.
REPRODUCTION
External sexual reproduction for the most part. A few bivalves and gastropods are hermaphrodites, so their sexual reproduction is internal. Some organisms, like oysters, change their sex as they mature.
BODY PLAN
Mollusks are protostomic coelomates. Coelomates have fluid-filled cavities that are surrounded by both the mesoderm and endoderm. Protostomes are multicellular organisms whose mouths develop from the primary opening in a developing embryo. Mollusk also have a thin layer of tissue called a mantle, which covers the body organs. Mollusks, moreover, have a three-part body plan, which includes a head, foot, and visceral mass (which includes the mantle).
MOLLUSK BODIES
Muscular Foot - used for locomotion/movement, clinging to surfaces, swimming, and burrowing.
Visceral Mass - Inside the mollusk; includes digestive, nervous, excretory, reproductive and respiratory systems.
Mantle - epidermal tissue surrounding the mollusks' internal organs; under the shell (see image above).
CIRCULATORY SYSTEM
Most mollusks have an open circulatory system, in which the blood is pumped out of vessels into open spaces surrounding the body organs. This enables animals to diffuse oxygen and nutrients into tissues that are bathed in blood and also to move carbon dioxide from tissues into the blood. Blood flows freely and is not restricted here. This is a good adaptation for slow-moving animals, like clams. However, cephalopods have a closed circulatory system, in which blood is confined to vessels as it moves through the body. Close circulatory systems efficiently move oxygen and nutrients to cells, where they are converted to usable forms of energy. This is a good adaptation for fast moving animals, like octopi and squids. Yet, all mollusks have hearts.
EXCRETION
Mollusks have an anus, which, of course, get rid of some wastes. The metabolic waste is filtered by the nephridium. After the nephridia filter the blood, waste is passed out through the anus as well as the mantle cavity. Nephridia are evolutionary adaptations enabling mollusks to efficiently maintain homeostasis in their body fluids.
MY THOUGHTS
The largest mollusks are the giant squid and giant clam, both of which are pretty amazing and beautiful animals. It's interesting that oysters can make huge "pearls" as they develop. That is a really cool natural process. Is that why they are called "treasures of the sea?" People today see pearls as rare gems. So, it is interesting that we, as humans, place so much value on these objects created by bivalves.It is also interesting to examine that octopi are capable of complex learning, such as being trained to select objects or certain shapes, colors, or textures.
• Live in a vast range of habitats - both aquatic and terrestrial.
• Vary in size.
• Most mollusks are marine.
• Most have a shell.
TYPES
Gastropods - snails and slugs.
Bivalves - clams, oysters, mussels, and scallops.
Cephalopods - octopi, squids, cuttlefish, and nautili.
SYMMETRY
Bilateral.
REPRODUCTION
External sexual reproduction for the most part. A few bivalves and gastropods are hermaphrodites, so their sexual reproduction is internal. Some organisms, like oysters, change their sex as they mature.
BODY PLAN
Mollusks are protostomic coelomates. Coelomates have fluid-filled cavities that are surrounded by both the mesoderm and endoderm. Protostomes are multicellular organisms whose mouths develop from the primary opening in a developing embryo. Mollusk also have a thin layer of tissue called a mantle, which covers the body organs. Mollusks, moreover, have a three-part body plan, which includes a head, foot, and visceral mass (which includes the mantle).
MOLLUSK BODIES
Muscular Foot - used for locomotion/movement, clinging to surfaces, swimming, and burrowing.
Visceral Mass - Inside the mollusk; includes digestive, nervous, excretory, reproductive and respiratory systems.
Mantle - epidermal tissue surrounding the mollusks' internal organs; under the shell (see image above).
CIRCULATORY SYSTEM
Most mollusks have an open circulatory system, in which the blood is pumped out of vessels into open spaces surrounding the body organs. This enables animals to diffuse oxygen and nutrients into tissues that are bathed in blood and also to move carbon dioxide from tissues into the blood. Blood flows freely and is not restricted here. This is a good adaptation for slow-moving animals, like clams. However, cephalopods have a closed circulatory system, in which blood is confined to vessels as it moves through the body. Close circulatory systems efficiently move oxygen and nutrients to cells, where they are converted to usable forms of energy. This is a good adaptation for fast moving animals, like octopi and squids. Yet, all mollusks have hearts.
EXCRETION
Mollusks have an anus, which, of course, get rid of some wastes. The metabolic waste is filtered by the nephridium. After the nephridia filter the blood, waste is passed out through the anus as well as the mantle cavity. Nephridia are evolutionary adaptations enabling mollusks to efficiently maintain homeostasis in their body fluids.
MY THOUGHTS
The largest mollusks are the giant squid and giant clam, both of which are pretty amazing and beautiful animals. It's interesting that oysters can make huge "pearls" as they develop. That is a really cool natural process. Is that why they are called "treasures of the sea?" People today see pearls as rare gems. So, it is interesting that we, as humans, place so much value on these objects created by bivalves.It is also interesting to examine that octopi are capable of complex learning, such as being trained to select objects or certain shapes, colors, or textures.