If you have ever gone to the beach and collected sea shells, you have been in contact with a mollusk. From the Latin "molluscus" meaning soft, these animals are characterized by soft bodies and an internal or external shell. Phylum Mollusca contains the first animals to exhibit a true coelom, meaning they had a fluid filled cavity to support specialized organs.
Mollusks all developed from one ancestor and have four common body parts. A calcium carbonate shell that is secreted by a thin tissue covering called the mantle. They have a muscular foot which can be adapted for crawling, burrowing, or as tentacles. Their internal organs are contained in a visceral mass.
Radula
Most mollusks have a tongue covered in teeth. It can be used to drill so that animals can attach to surfaces or eat animals with hard shells. It is also used to scrape food such as algae off of surfaces.
Most mollusks have a tongue covered in teeth. It can be used to drill so that animals can attach to surfaces or eat animals with hard shells. It is also used to scrape food such as algae off of surfaces.
Trochophore Larva
All mollusks except cephalopods go through indirect development. They hatch as a planktonic stage called trochophore larva which is free swimming.
All mollusks except cephalopods go through indirect development. They hatch as a planktonic stage called trochophore larva which is free swimming.
Gastropoda
This class includes snails, slugs, and winkles. They can be marine or terrestrial. There are over 90,000 species of gastropods. The name gastropod means "stomach foot" since, unlike other mollusks, their foot is on their ventral surface. Gastropods go through a process called torsion where their body twists 180 degrees and their anus ends up dorsal to their heads.
This class includes snails, slugs, and winkles. They can be marine or terrestrial. There are over 90,000 species of gastropods. The name gastropod means "stomach foot" since, unlike other mollusks, their foot is on their ventral surface. Gastropods go through a process called torsion where their body twists 180 degrees and their anus ends up dorsal to their heads.
Bivalves
All bivalves have two shells as indicated by the prefix "bi." They are the only mollusks without heads and without radulas. They develop indirectly from trochophore larva and are sessile as adults. They dig into the ground using their muscular foot and use their siphons to take in and release water. |
Cephalopoda
Nautilus, squd, cuttlefish and octopi all have arms and or tentacles that they can use to fight, eat, or travel.