Anatomy & Classes
Bivalvia: bivalves are two-shelled organisms that, through time, have lost their radula as well as their head to adjust to their filter-feeding lifestyle. Their lacking a head and a radula are considered extremely unique characteristics among mollusks. Some bivalves are sessile and either attach themselves to a hard surface, such as a rock, or bury themselves into the ocean floor. However, most are free moving and can propel themselves or use their muscular foot to move. Some bivalves are parasites during their larval stages, these are known as "glochidia".
Source: http://www.pznow.co.uk/marine/bivalves.html
Cephalopoda: the cephalopods, like the bivalves and gastropods, have unique characteristics; they have tentacles that act as arms, they have three hearts (two pump blood to the gills, the largest pumps blood to the rest of the body), most lack a shell (except nautiluses), they are very intelligent (except nautiluses), they have chromatophores, and a closed circulatory system. Their tentacles are attached directly to their heads. They also have incredibly good eyesight...except nautiluses. Cephalopods are well-known for being masters of camouflage. They can change the color of their skin and change the look of their skins' texture as well. Some octopuses also mimic other animals. Cephalopods were initially large in numbers but were quickly out-competed by more efficient predators and eventually evolved to be excellent camouflagers and intelligent...except nautiluses. Cephalopods use jet propulsion via their siphons to get around.
Source: http://animals.about.com/od/molluscs/p/cephalopods.htm
Gastropod: the largest class of Mollusca, some gastropods lack a shell (slugs) and others have a shell (snails). Snails are capable of withdrawing into their shells for protection. Gastropods have a very interesting characteristic known as torsion, which is a process that gastropods go through as a larva; their organs flip 180 degrees from top to bottom.
Source: http://marinelife.about.com/od/invertebrates/p/Class-Gastropoda-Snails.htm
Source: http://www.pznow.co.uk/marine/bivalves.html
Cephalopoda: the cephalopods, like the bivalves and gastropods, have unique characteristics; they have tentacles that act as arms, they have three hearts (two pump blood to the gills, the largest pumps blood to the rest of the body), most lack a shell (except nautiluses), they are very intelligent (except nautiluses), they have chromatophores, and a closed circulatory system. Their tentacles are attached directly to their heads. They also have incredibly good eyesight...except nautiluses. Cephalopods are well-known for being masters of camouflage. They can change the color of their skin and change the look of their skins' texture as well. Some octopuses also mimic other animals. Cephalopods were initially large in numbers but were quickly out-competed by more efficient predators and eventually evolved to be excellent camouflagers and intelligent...except nautiluses. Cephalopods use jet propulsion via their siphons to get around.
Source: http://animals.about.com/od/molluscs/p/cephalopods.htm
Gastropod: the largest class of Mollusca, some gastropods lack a shell (slugs) and others have a shell (snails). Snails are capable of withdrawing into their shells for protection. Gastropods have a very interesting characteristic known as torsion, which is a process that gastropods go through as a larva; their organs flip 180 degrees from top to bottom.
Source: http://marinelife.about.com/od/invertebrates/p/Class-Gastropoda-Snails.htm
Digestion
The organisms of each class of Mollusca have their own special way of acquiring and digesting prey...
Bivalves: bivalves don't actively hunt for food like cephalopods and gastropods do. Since they're filter feeders, they simply suck water into their mouths which then makes its way into the stomach where the food particles in the water are digested. The intestines then remove nutrients from the food and the waste is emptied by the anus. The flow of the excurrent canal carries away waste.
Cephalopods: cephalopods are deadly and can be very aggressive predators. They are strictly carnivorous. Cephalopods use their tentacles and the suckers to grab prey and keep them from getting free. They use their tentacles to pull prey close to their mouths. Once their food has entered their mouth, it goes past the beak that breaks up the food. The bits of food are moved to the stomach and broken down, any nutrients are extracted by the intestines. And leftover waste is then expelled by the anus.
Gastropods: carnivorous gastropods are capable of drilling a hole into shells of their victims by using their radula. When they've acquired prey, it first is stored in the crop. It is digested by the stomach and nutrients are removed in the intestines. Waste is removed by the anus.
Bivalves: bivalves don't actively hunt for food like cephalopods and gastropods do. Since they're filter feeders, they simply suck water into their mouths which then makes its way into the stomach where the food particles in the water are digested. The intestines then remove nutrients from the food and the waste is emptied by the anus. The flow of the excurrent canal carries away waste.
Cephalopods: cephalopods are deadly and can be very aggressive predators. They are strictly carnivorous. Cephalopods use their tentacles and the suckers to grab prey and keep them from getting free. They use their tentacles to pull prey close to their mouths. Once their food has entered their mouth, it goes past the beak that breaks up the food. The bits of food are moved to the stomach and broken down, any nutrients are extracted by the intestines. And leftover waste is then expelled by the anus.
Gastropods: carnivorous gastropods are capable of drilling a hole into shells of their victims by using their radula. When they've acquired prey, it first is stored in the crop. It is digested by the stomach and nutrients are removed in the intestines. Waste is removed by the anus.
Representative Organism:
- Part of the class cepalopoda
- Scientific name: Enteroctopus dofleini
- Common name: Giant pacific octopus
- Have an arm span of about 14 feet, can be about 20 feet long
- Can weigh up to 150 pounds
- Largest giant pacific octopus ever recorded was about 30 feet long
- Eat mostly fish, shrimp, crab, scallop, and other shellfish
- They are very adaptable and are good at resisting the effects of human pollution
- They are capable of moving more than 700 pounds
- They can be found in the Northern Pacific Ocean and from Alaska to California. They prefer living in rocky areas or caves and kelp
Source: http://www.neaq.org/animals_and_exhibits/animals/giant_pacific_octopus/