Part 3 of our “Smorgasbord of Food Offerings from the Sea” series
By Janice Edwards
If you have been following the previous posts in this series, you know we have had sea pork and sea apples as part of our Smorgasbord of Food Offerings from the Sea series. To round out our menu, we have the sea urchin Clypeaster roseaceus commonly known as a sea biscuit. Sea biscuits can be found in shallow tropical and temperate waters.
What’s In a Name Question #1 or Why Do They Call It That: The genus name, Clypeaster, is Latin for the outward appearance of these animals --”clypeus” means round shield and “aster” means star. How interesting that a marine animal sports the shape of a flower on its body!
The genus Clypeaster is in the phylum Echinodermata which, in addition to sea urchins, also includes starfish, sea lilies, and sea cucumbers. Sea biscuits tend to be more oblong and rounded than their cousins, the sand dollar. Both sea biscuits and sand dollars have a mouth midway on their underside and anus at the end, and as such are called irregular urchins.
What’s in a Name Question#2 or Regular vs. Irregular: Regular echinoids, or sea urchins, have no front or back end and can move in any direction. (Picture a spiny sea urchin in your mind.) Their longer, often painful-to-predators spines help protect them as they move around. Irregular echinoids have a definite front and back and move in a particular direction, often burrowing in sediment. Irregular urchins are considered to have evolved from an ancestral regular urchin form. Thus, anatomical characteristics exhibited by irregular urchins are thought to represent modifications to the anatomy of regular forms. Most echinoderms exhibit bilateral symmetry as larvae, meaning they can be divided into matching halves by drawing a line down the center. During development, echinoderms become five-fold (i.e., pentamerous) symmetrical, meaning they can be split into five similar segments around a central axis (center of the body). Irregular urchins exhibit secondary bilateral symmetry; as adults these organisms display bilateral symmetry, but in a manner unlike that they possessed as larvae.
Because sea biscuits have a different lifestyle than the regular sea urchins, they don’t need their spines for defense. Therefore, their spines are shorter and more hair-like. In other words, they are modified to help the sea biscuit move around in sediment where they live and feed. Notice the spines in the pictures of the sea biscuit below:
Take a look at this video of a sand dollar moving through sediment in much the same way as a sea biscuit:
Sea biscuits use small tube feet/spines on their underside to transfer sediment containing food particles into their mouth. Kind of like a set of conveyor belts! Echinoids graze off the substrate using a jaw apparatus known as an Aristotle’s Lantern. Sea biscuits and sand dollars have a modified form of Aristotle’s Lantern that they use to crush and grind sand.
What’s in a Name Question #3 or Why is it Called Aristotle’s Lantern: It’s named after the Greek scientist and philosopher Aristotle, of course. Some scientists thought his writings referred to the jaw apparatus looking like a kind of a lantern, specifically a horn lantern. However, this has recently been suggested to be a mistranslation. Aristotle's lantern may actually refer to the globular shape of whole echinoids, which resemble the ancient lamps of Aristotle's time.
Aristotle’s Lanterns contains not one, not two, but five teeth ! Ouch!
Check out these pictures of a sea biscuit found in the Atlantic Ocean off the North Carolina coast and housed in the NC Museum of Natural Sciences collection:
Although not in the most pristine condition, one can still see the rounded shield-like shape and the remnants of a petal-like “star.” It is about 6-½ inches long.
For dinner tonight, a 3-course meal: Grilled sea pork sauteed with sea apples and served with sea biscuits for you carb lovers out there.
Part 2 of our “Smorgasbord of Food Offerings from the Sea” series