Dive Dry with Dr. Bill

#240: Have a Heart... Urchin

As an avid reader of this column, you probably think I'm going to focus on my favorite "M" word, Mating, or possibly my second favorite one, Munching (I love M & M's). Heck, you probably think those are the only two subjects I'm capable of writing about. Well, I'm going to fool you. This week I will talk about matters of the heart, but not romance or what evolves naturally from that. No, I'm going to introduce you to the heart urchin. California has several species, but the scientific name of the most common one, Lovenia, sounds as if it was inspired by romance, but it was actually named after an early scientific researcher, S. L. Loven.

99.9% of my readers are probably asking "What is a heart urchin?" Almost all of you have heard of sea urchins. No, these aren't poor little waifs in the sea whose parents have abandoned them. Sea urchins are relatives of the starfish (oops, sea stars... must be PC about this) and sea cucumbers (hmmm, I don't think the PC crowd has come up with a replacement name for these so I'm safe). Along with the brittle stars, they all belong to the phylum Echinodermata or spiny skinned animals. People often confuse the sea urchins with the soft-bodied sea anemones. Urchins have hard calcium carbonate outer skeletons (exoskeletons) known as tests. For defense they have sharp spines sticking out in all directions from the upper surface of the test. Sea anemones have soft tentacles, but they are often armed with stinging cells known as nematocysts.

Most conventional sea urchins are round or spherical in shape. If they're smart, they remain hidden in rock crevices during the day so sheephead, lobster, sea otters and other predators don't make a delicious meal of them. After all, their eggs or roe are served as sushi by the Japanese who call the dish "uni." One of the first things I ever ate fresh from the sea was the roe of a green sea urchin (a close relative of the red and purple urchins in our waters) collected off the coast of New Hampshire when I was a young marine biology student at Harvard. Today I don't harvest urchins for my eating pleasure, and prefer my sushi at Flip's.

The heart urchin (sometimes referred to as the sea mouse or sea porcupine) takes on a different shape, like their other "eccentric" sea urchin relatives the sand dollars. They are oval like an egg, and show signs of bilateral (two-sided) symmetry instead of strictly following the five part radial symmetry of their more traditional relatives. Because of this they actually have a front and rear end, as well as left and right sides. Can't say that for our other urchins including the sand dollars! They retain spines, but they are curved back along the test rather than being erect. Why have they adopted this unique "architectural" design? Because of where and how they feed. Form follows function. Unlike "normal" sea urchins, which usually remain on rocky surfaces or use their sharp jaws to burrow into the rock to create shallow protective holes, the heart urchins live on or under the surface of soft, sandy bottoms.

Living under the sand, the bilateral shape makes it much easier for them to plough under the surface of the substrate searching out food. A round shape would be much more difficult to move in one direction... it might just travel in endless circles. Because its long, slender spines curve backwards over the upper surface of the test, they give it a hydrodynamic (or should it be sand-o-dynamic?) shape. Thick, erect spines would stop it dead in its tracks. Unlike "normal" sea urchins, which have their mouths in the center of the test, the heart urchin has its mouth at one end... and its anus at the other.

Our most common local species of heart urchin is found from San Pedro south to Panama and the Galapagos Islands. It lives on soft substrates down to depths of up to 500 feet. Most sources suggest the maximum length of these echinoderms is about three inches, but I have seen ones in the four inch range. The added length was real, not due to the magnification properties of being underwater which are undoubtedly the cause of "fish tales" told by spearfishers!

During my research for this column, I discovered that heart urchins "breathe" (obtain oxygen and expel carbon dioxide) by extending their tube feet above the surface of the sand and into the surrounding water. This is kind of like a snorkeler swimming at the ocean's surface with their snorkel sticking up above the water to breathe. When I lived at Toyon, I had an old M38-A1 military jeep that was entirely "water proof" (it had to be with my driving). My jeep had a "snorkel" that could be attached to its carburetor so I could drive it into the sea. Fortunately I wasn't that much of a party animal!

Those of us familiar with the early James Bond films... you know, the ones that feature the real James Bond... know that if bathers or divers step on the sharp spines of regular sea urchins it can be quite painful. Of course the thought of biting the urchin spine out of Domino Derval's (Claudine Auger's) foot was a youthful fantasy of mine. I discovered on the Internet that instead of being a symbol of love, the heart urchin can break your heart... or at least your skin. When it senses potential danger, it points its sharp spines in that direction. If a bather steps on one in the surf, it can quickly turn into a cold "heart" and puncture the foot. Now that's an example of when "love" hurts!

© 2007 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles," "Gentle Giants: Giant Sea Bass" or "Common Fish and Invertebrates of the Sea of Cortez" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

The bilaterally symmetric test of the heart urchin; inside showing ambulacral grooves and holes for tube feet.

This document maintained by Dr. Bill Bushing.
Material and images © 2007 Star Thrower Educational Multimedia