Mollusca
Classes (there are 7, but we will only look at 3)
Class Gastopoda-Slugs & Snails
Class Bivalvia-Two-shells, ex: oysters
Class Cephalopoda-squid, octopus, etc
Class Gastopoda-Slugs & Snails
Class Bivalvia-Two-shells, ex: oysters
Class Cephalopoda-squid, octopus, etc
Anatomy
General Information
Mollusks usually have a shell. In clams, oysters, mussels and snails this is an external shell; in squid and octopi this is internal. They are bilaterally symmetrical coelomates. Mollusks do not have body segmentation. Most mollusks have 3 body regions: a head, a visceral mass, and a "foot". The head consists of the brain and any sense organs the organism may have, the visceral mass contains the internal organs. The "foot" is actually the lower part of the body. It is very muscular and is used for movement or to dig through sand. It is called the foot because this is the part that comes into contact with the ground.
Mollusks also have a mantle. The mantle contains the gills and anus and is responsible for secreting the CaCo3 shell.
Some mollusks, like snails, have a radula. This acts as a rough tongue and is used to rasp at food.
Nervous System
Mollusks have 2-3 main nerve cords. Some have brains--if they do, the brain is located around the esophagus. Mollusks have eyes and sensor-containing tentacles which can detect chemicals and movement in the water.
Reproductive System
Most mollusks use external fertilization as their method of reproduction. These organisms remain one gender their whole life. Mollusks that use internal fertilization are typically hermaphroditic.
Digestive System
Mollusks have a fairly well-developed digestive system. Some mollusks use radula to obtain their food while others use beaks to tear at their prey. All mollusks' mouths contain a mucus which the food will stick to. Cilia along the digestive system will move the food towards the stomach forming a "food string"--a long string of slimy, mucus-y food (yum!)
Circulatory System
Mollusks have an open circulatory system. The heart and other body organs, including nephridia, are found in the main body cavity (the hemocoel). The blood contains hemocyanin that will carry oxygen from the gills to the organs.
General Information
Mollusks usually have a shell. In clams, oysters, mussels and snails this is an external shell; in squid and octopi this is internal. They are bilaterally symmetrical coelomates. Mollusks do not have body segmentation. Most mollusks have 3 body regions: a head, a visceral mass, and a "foot". The head consists of the brain and any sense organs the organism may have, the visceral mass contains the internal organs. The "foot" is actually the lower part of the body. It is very muscular and is used for movement or to dig through sand. It is called the foot because this is the part that comes into contact with the ground.
Mollusks also have a mantle. The mantle contains the gills and anus and is responsible for secreting the CaCo3 shell.
Some mollusks, like snails, have a radula. This acts as a rough tongue and is used to rasp at food.
Nervous System
Mollusks have 2-3 main nerve cords. Some have brains--if they do, the brain is located around the esophagus. Mollusks have eyes and sensor-containing tentacles which can detect chemicals and movement in the water.
Reproductive System
Most mollusks use external fertilization as their method of reproduction. These organisms remain one gender their whole life. Mollusks that use internal fertilization are typically hermaphroditic.
Digestive System
Mollusks have a fairly well-developed digestive system. Some mollusks use radula to obtain their food while others use beaks to tear at their prey. All mollusks' mouths contain a mucus which the food will stick to. Cilia along the digestive system will move the food towards the stomach forming a "food string"--a long string of slimy, mucus-y food (yum!)
Circulatory System
Mollusks have an open circulatory system. The heart and other body organs, including nephridia, are found in the main body cavity (the hemocoel). The blood contains hemocyanin that will carry oxygen from the gills to the organs.
Gastropods
- Snails, Slugs, Nudibranchs
- Live on land and water
- Have a radula that scrapes/bites off food
- Move using a muscular foot that is typically mucus-covered
Bivalves
- Clams, Oysters, Mussels, Scallops
- Shell is excreted by the mantle
- Uses foot for movement, attachment, or jet propulsion
- Filter feeders
Cephalopods
- Squid, Octopus, Nautilus, Cuttlefish
- Most well-developed/intelligent of the mollusks
- Octopi can actually learn behaviors
- Have tentacles used to catch prey
- Move using jet propulsion
- Squid and Octopi can eject ink for protection
- Most have some form of camouflage using chromatophores