Brachiopods versus Bivalves
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Modiomorpha (bivalve) specimen from our collection
Laqueus (brachiopod) specimen from our collection
Borrowed from a Friday Harbor blog

This one's for you, Dan!

What are the differences between brachiopods and bivalves, and how do you tell them apart?
The first thing one might notice if looking at them from a taxonomic viewpoint is that they belong in different phyla. Brachiopods are in the phylum Brachiopoda while bivalves are in the phylum Mollusca. This means that bivalves are related to the other molluscs (snails, cuttlefish, squids, nautiloids, octopus, etc.) while brachiopods are related to... brachiopods.

So taxonomically things are looking pretty distinct. On to the insides!
Both brachiopods and bivalves have two major muscles within the shell to keep it closed. Brachiopods have what are called adductor muscles. These muscles contract to keep the two valves closed. Bivalves also have adductor muscles that contract to keep the valves closed. So why do I bring this up as a difference? Bivalves have a second structure that separates them from the brachiopods. This structure is a ligament that joins the valves dorsally. When the adductor muscles in a bivalve relax, the ligament forces the two valves (shells) open. This is why bivalve shells (of dead bivalves) are often found in a "butterfly pattern" where both valves have opened in a pattern reminiscent of butterfly wings.

 

The absence of a ligament like this in brachiopods means that when brachiopod shells (of dead brachiopods) are found, both valves are often found closed up as though the animal were still alive.

 

Feeding systems are also completely different between the two groups. Brachiopods feed by means of a lophophore. This structure has a series of ciliated tentacles that can be extended to create a current which allows the brachiopod to catch food particles from seawater.

 

 

 

 

Jessica Utrup is the museum assistant in the Division of Invertebrate Paleontology at the Yale Peabody Museum

Taken from the following blog: Spineless Wonders

HI Jessica This is very

HI Jessica

This is very good. A suggestion: you mention the feeding system of brachiopods, but then don't go on to compare it with the feeding system of bivalves. A comparison would be helpful.

Cheers

Steve

Steve,Excellent point. I do

Steve,

Excellent point. I do more work on brachiopods than bivalves, so I only focused on the brachiopods. Bivalves have a muscular foot. Often, an extension of this foot will be used as an inhalan siphon. This siphon draws water into the shell. From there, the water passes over the gills. Oxygen is removed by the gills themselves, and food particles are captured by food grooves located on the gills. These food particles are coated by mucus and carried by cilia to the mouth region where they are ingested. Bivlaves have no hard internal structure to support any feeding mechanisms.

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