Is there anything more fitting than a heart urchin for Valentine’s Day? If you’ve been walking along Sanibel’s Gulf beaches recently, you may have noticed a heart-shaped urchin test in the wrack line. The test is a hard internal skeleton (endoskeleton) composed of calcium carbonate plates. When the animal’s alive, it’s covered in thin skin and spines, hiding the test. Typically, when they wash up on the beach, the spines and skin have brushed off, leaving the exposed, fragile test. A more recognizable and common test that washes up is from sand dollars. If an echinoderm washed up onshore still has skin and spines, it’s possible it’s still alive, and it’s best to return it to the ocean. 

Named for their unique shape, heart urchins are a special group of urchins under the order Spatangoida. While true sea urchins are typically spherical and covered in long, sharp spines that stick up for protection, heart urchins have an elongated shape with short velvety spines for burrowing in the sand. Unlike true sea urchins, which are found living on top of the sand or rocks, heart urchins spend most of their lives buried underneath the sediment.

The species washing up on Sanibel is Echinocardium cordatum, commonly known as the sea potato. Fitting to its name, sea potatoes are “baby potato” shaped heart urchins with yellowish spines. They have a star-shaped pattern on their top side, called an ambulacrum, which facilitates movement and respiration. Sea potatoes burrow 10-15 centimeters into the sand and have two mucus-lined channels that allow the creature to breathe and access food while remaining safely buried. They eat detritus (decaying organic matter) that accumulates at the top of their burrow. 

It is uncommon to find a sea potato test on the beach. The recent sightings on Sanibel are most likely due to the cold water temperatures of the past couple of weeks, which have affected many other marine invertebrates and fish.

Whether you are looking for a marine-themed Valentine’s Day activity or excited to see a unique creature, take a beach walk and check out the wrack line to find these festive heart urchins this weekend! <3

Learn more about echinoderms on one of our weekly beach walks! We partner with local resorts to offer unique, on-property ocean-learning opportunities for guests and visitors. Learn more about these beachwalks at sanibelseaschool.org/programs/at-your-resort. 

Contributing Author: Jordyn Sateren  

Resources:

https://www.inaturalist.org/taxa/122232-Echinocardium-cordatum#cite_note-:0-1

https://www.marinespecies.org/aphia.php?p=taxdetails&id=124392

https://ecology.wa.gov/blog/february-2017/eyes-under-puget-sound-critter-of-the-month-the-h