Mollusks are a very large group of animals. They vary in size from the giant colossal squid to the tiny burrowing snail. The “brains” of this group escape tanks and change color. Nudibranchs are very toxic and colorful. Some snails have very elaborate shells and can be quite large. Some don’t have shells. The diversity among the creatures is amazing.
The group commonly know as bivalves includes clams, mussels and oysters. They have two shells that open and close. Some clams, mussels and oysters are used for food. Most of the shells look generally the same. The shells in Fig 1 are a few in this category. Clams have a foot that burrows in the ground and have two syphons (Fig 1). The syphons act as a snorkel and pump water out of its burro. They are all filter feeders.
Gastropods (meaning stomach foot) are commonly known as snails. Most snails have shells. The ones that do have shells either have a cone shaped shell or the more common spiral shell. They are also jelly shells and some gastropods have their shell under their skin. Muscles and clams are related to the snails. But the bivalves do not quite have the array of colors that the majority of the gastropods have.
Octopi are probably one of the most clever mollusks. They have been known for climbing out of tanks and escaping. Most octopi have a special organ for changing color. For example: the Blue Ringed Octopus rings turn blue when intimidated (to warn predator that he is poisonous). Some octopi can also change their skin texture to blend in with the environment around them perfectly.