Prairie Public NewsRoom

Giant Floater Clam

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Chuck Lura

I recently received a call about a clam at Lake Metigoshe. The caller had found one in the sediment along his shoreline and was wondering about it. I have never seen any clam shells around the lake, much less a live one. But with a little help from a colleague at Valley City State University I have tentatively identified it as a Giant floater (Pygandon grandis).

I don’t know much about clams, so I had to do some investigating. Clams have interesting common names, fat mucker, Wabash pigtoe, creek heelsplitter, deer toe, plain pocketbook. I checked Cvancara’s Aquatic Mussels of North Dakota from 1983. He documented 13 species of what are generally referred to as clams in the state along with 13 species of pill clams, which are very small clams, in the order of a few millimeters in length. He also documented 22 species of snails in the state.

The giant floater has a widespread range, occupying the Mississippi and Missouri drainages as well as the St. Lawrence, and in Canada from western Ontario to Alberta. It occupies a variety of habitats, but is mainly in the muddy bottoms of lakes and in areas of rivers and streams with slow moving water. It is a filter feeder, of course, and probably consumes mainly algae but likely consumes other microscopic life.

Sexuality and life cycles are variable in clams. Some species, for example, have both male and female reproductive organs, others may start out as male but become females as they age. A giant floater is either male or female, and they have an interesting life cycle. Fertilized eggs are held in the female for around 11 months in brood tubes where they develop into larvae. The larvae, or glochidia are then released into the water and must attach to gill filaments or the body surface of a host fish. But not just any species of fish will do. Known hosts for the giant floater include bluegills, black crappie, a few species of shiners and darters, creek chubs, and brook stickleback. After a few days or perhaps weeks, the larvae become juvenile and release from the host. They then find a place in the substrate and develop into adults.

~Chuck Lura

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