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What's this strange snail / rock thingy?

My daughter found this strange rock-like thing in our yard that seems to have snail-like shell shapes in it, all stuck together. It feels like some kind of calcium rocky thing. We've attached a couple photos, one from the front and one from the back. Any idea what this is? Thank you. Love the fact that you're available to answer these kinds of questions from people! :-)

Jason Freidenfelds, Santa Barbara - June 29, 2019

Curator Response

Hi Jason,

Thanks for sharing your interesting find! This looks like a cluster of shells from a colony of scaled worm snails, possibly Thylacodes squamigerus. These marine gastropods live in shells cemented to a surface (commonly a rock), so they stay in one place, unlike most snails. To eat, they cast out a mucus net (yum) that catches plankton, detritus, and other morsels, then reel in the net to feed on their catch. We’ve had them in Sea Center habitats from time to time, and you often run across these empty shell clusters when walking on local beaches.

Interesting that you found this in your backyard! This probably reflects that someone else found it fascinating enough to pick up and bring home. It’s good to note that while collecting objects like this is permitted in some areas, it’s forbidden to remove anything from marine protected areas like Coal Oil Point, so if you decide to start building your own collection of objects, be mindful of where you do your collecting.

Stay curious,

Invertebrate Zoology Collection Manager Vanessa Delnavaz, M.A., and Sea Center Live Collections & Husbandry Manager Thomas Wilson