The Mollusca is a phylum that composes largely of invertebrate animal known as mollusks. Around 85,000 species of molluscs are recognized currently. Molluscs are the largest marine phylum, making up about 23% of all the named marine organisms. Molluscs are not limited to saltwater environments, they can also live in freshwater and terrestrial habitats. This phylum is currently divided into 7 main classes:
There was an 8th class known as the Rostroconchia; however they have long been extinct. For a creature to be labeled as a Mollusca and be placed into one of these classes you must have these three universal mollusks defining features. The first one would be to have a mantle with a significant cavity used for breathing and excretion, second would be to have a radula, and third would be to have the structure of the nervous system.
- Gastropoda (single shelled cowries, cones etc.)
- Bivalvia (two shelled like clams, mussels etc)
- Aplacophora (solenogasters)
- Monoplacophora (segmented limpets)
- Polyplacophora (or Amphineura; however, perviously it was called Chitons)
- Scaphopoda (tusk shells)
- Cephalopoda
There was an 8th class known as the Rostroconchia; however they have long been extinct. For a creature to be labeled as a Mollusca and be placed into one of these classes you must have these three universal mollusks defining features. The first one would be to have a mantle with a significant cavity used for breathing and excretion, second would be to have a radula, and third would be to have the structure of the nervous system.
Loligo pealeii (Longfin Inshore Squid)
Squids lack teeth, but they have other hard mouthparts that they use to break food down before passing it into their digestive tracts. From the mouth, food must move through the throat and esophagus before it can wind up in the stomach where true digestion begins. For the most part, squids have a smaller stomach, a shiny white sac, attached to a larger organ known as the caecum. Materials that are devoid of nutrient value pass through the mantle and out through the squid’s funnel into the surrounding water. Squid waste is solid so they can prevent getting their own excrement in their gills.
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Bradybaena similaris (Asian trampsnail)
Snails break up their food using a radula, a chitinous tongue-like structure with a lot of microscopic hooks called cuticulae which serve as teeth. After the snail scrapes off its food of a material, the food is then transported to the digestive tract. The digestive tract starts at the head with the mouth, continues down to the esophagus, then to the crop, where food is stored.
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Tonicella lineata (Lined chiton)
Most chitons are herbivorous - feeding on unicellular and multicellular algae.They scrape alga off of the rocks and other substrates on which they live, by means of their hard, raspy radular ribbon. The mouth is located at the anterior end, in front of the foot and opens into a buccal cavity containing the radula. When the radula is retracted, these food particles are pressed against the roof of the buccal cavity and carried into the esophagus.The esophagus then enters an irregularly shaped stomach that contains a large ventral sac. Digestive enzymes are added to create a slurry to make the food pass easier. All waste materials pass through a sphincter, where waste is condensed in to pellets for it to pass through the anus.
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