Thursday, August 20, 2009

What are those strange rubber circles on the beach?

It seems like several times a summer someone ask me about "those strange rubber circles" they find on the beach. These are the sandy egg cases of Lewis's Moonsnail, Euspira lewisii. The eggs are laid in this distinctive collar, which is molded by the shape of the shell as it is released from the snail's body. The tiny eggs are spread out in the jelly-like center layer and then both sides are covered with sand; they will hatch in about 6 weeks. These egg collars are regularly found in the intertidal zone from April to September.

Lewis's moonsnail laying its eggs in our touch tank!

Moonsnails burrow in the sand to hunt clams. If you find a clam shell on the beach with a perfect hole in it, the clam was preyed on by a moonsnail. They drill holes in the clam shells and actively cut up the flesh of the clams with their tooth-like radula. Adults will eat about one clam every 4 days.

Doug Rogers, from Washington Dept of Fish and Wildlife, investigates a newly laid moonsnail egg collar (you can see an intact one under his hand). Doug was excited to see the handy work of this moonsnail, which he collected for us in the spring.

Information referenced from Marine Life of the Pacific Northwest, by Andy Lamb and Bernard Hanby; and Shells and Shellfish, by Rick Harbo
See you soon!

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