In which I make an effort to learn about bivalves

Until recently, I haven't spent a lot of time on bivalves. Other than as ingredients in a marinara sauce, that is. But now I've been focussing on the crunchy bits on the outside, rather than the juicy insides. It turns out that — contrary to my gastropodal preconceptions — bivalve shells don't all look the same.

Here's one I prepared earlier.

Laternula (family Laternulidae, subclass Anomalodesmata) is a small genus of bivalves living in soft sediments in the Indo-Pacific and Southern Oceans. A few species are common in southern Australia.



Laternulids are easily distinguished from other families. The shells are thin and fragile and are attached to one another by a tricky hinge operated with a pair of ligaments. As with other bivalves, the main ligament is a wedge of elastic protein. Because the shells are so fragile, this ligament is attached to spoon-shaped chondrophores that project into the shell cavity rather than directly to the shell edge. This ligament is also strengthened by a calcareous plate, the lithodesma.


The secondary ligament, which is on the outside of the shells, is formed from a continuous layer of periostracum. Weird, huh?

Laternulids have a few other strange features, such as a fine split in each shell that allows the shells to flex. But then they have an internal buttress that reduces the potential for damage … You can see them both in the photo below.

No wonder they spend all their time sitting in soft mud.