Does Anyone Know What This Is? Our Caribbean Sea Mystery Solved!

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This week, my curiosity finally peaked! For years, we've been snorkeling here in the Caribbean and spotting these unusual fluted edged circles of sand on the sea floor. What do they feel like? They're sandy and feel like they're held together with something sticky. When it's dry, it crumbles like dry sand. For a long time, I've joked about them being conch poop; but never really gave it much thought until this week. I thought to myself, "There's no reason to allow this mystery to continue as there must be an answer somewhere on the internet". The first thing I did was post the photos on Facebook, guessing that some of our sea-faring friends would have the answer. Their replys were amazingly creative. The irony is that a family member who has only been snorkeling a few times in her life came up with the answer!

This neat thing is a Moon Snail sand collar, or an egg case. There are tiny eggs sandwiched between sand particles. I contacted Dr. Thomas Huelsken, a Research fellow of the Deutsche Forschungsgemeinschaft (DFG) School of Biological Sciences at the University of Queensland in Australia. His research focuses on sand-associated gastropods, particularly Moon Snails

He confirmed our information and told us that size of a sand collar is dependent on two things: 1. the shell size, 2. the foot size. The snails make the collar by rotating around themselves producing the egg collar with their propodium (front part of the foot). Thus, the center of the egg mass is (more or less) identical to the shell size. Usually the center is a bit bigger than the shell because of the constant movement of the snail during egg mass production. The diameter of the collar band is directly related to the size (length) of the propodium. In our case, he assumes (taken my thumb with 2 cm into account) the specimens' shell was 3-5 cm long (1.5 - 2 inches) with a propodium of similar size. From the morphology of the collar, he suggested that we were looking at a Polinices species (P. hepaticus, P. lacteus). These species can grow up to 40 mm shell length and up to 12 cm total length.

So, with one mystery solved...what's next? Hmm...I am sure we will think of something!