Mollusks: Bivalves and Univalves
What are bivalves and univalves, and what are the differences between the two? This article describes these two popular mollusks.
If you’ve ever wondered what a bivalve is or a univalve is, they are both mollusk. A mollusk is a type of shellfish, and each of these two types describes what the outer shell is. Both are best purchased fresh and live, or if caught kept properly. To test if a bivalve is alive, the shells will close shut if it is tapped or touched. Toss out any that are still open and do not close after purchasing. Univalves will retract if touched at the operculum, which is a thin piece of shell that is attached to its foot that can seal up the shell if needed for protection.
Univalves
Univalves are as the name suggests – ‘one’ shell or a shell having one piece. Univalves are also known as Gastropods. A mollusk with a univalve shell has usually a foot and head that live inside the shell, and can extend or retract outside or inside the shell. Univalves can live in the water or outside the water.
Examples of univalves include periwinkles, snails, abalone and conch.
Image above shows a Queen Conch shell, an example of a univalve. Image courtesy of Tami Heilermann, US Fish and Game.
Bivalves
Bivalves consist of two shells. Unlike the univalve type of mollusk, the bivalves generally do not have a head, just the body that resides in between to shells that open and close at will, usually to feed. Some have a very long foot that either digs or attaches itself onto things. Bivalve mollusks can be found as fresh or saltwater varieties.
Image above shows a freshwater mussel. Image courtesy of Phillip Westcott, US Fish and Game.
Examples of bivalves include scallops, clams, oysters and mussels.
Image above shows a Brook Floater and a Northern Lance, examples of bivalves. Image courtesy of Phillip Westcott, US Fish and Game.
