Keeled Heart Urchin, Brissus latecarinatus: The Keeled Heart Urchin is normally about 4 cm (1.6 inches) long and 3 cm (1.2 inches) wide with reports that they reach 16.6 cm (6.5 inches). The width of the test of 77 percent to 85 percent of the length and has a normal well defined star shaped poetaloid pattern on the oral surface.
They are widely distributed in the Indo-Pacific oceans.
In Mexican waters they are found throughout the Sea of Cortez and along the coast of the mainland south to Guatemala.
The Keeled Heart Urchin is the only Heart Urchin found intertidally (versus subtidally) in sandy areas between 15 cm (6 inches) and 20 cm (8 inches) under the surface in waters of up to 150 feet deep.
The Keeled Heart Urchin is seldom seen by humans species belonging to Phylum Echinodermata and Class Echinoidea which includes Sea Urchins and Sand Dollars. They are members of the Spatangidae Family. They are named for the shape of their body and also sometimes called Sea Potatoes. The Urchins are of great scientific interest because, via fossil records, they date to the Cambrian Age (over 500 million years ago) with 7,000 living and 13,000 extinct species. Heart Urchins have tube feet and spines and they are not strictly symmetrical along five axes, thus they are sometimes referred to as irregular echinoids, but they have five-part symmetry.
The internal skeleton or test is formed out of large pieces of calcium carbonate fused together into plates in multiples of five. It is rigid and hollow without internal support. They have a mouth at one end and an anus at the other. They breath through their tube feet that extend through a petaloid, a series of tiny holes in the skeleton. They lack the specialized Aristotle’s lantern jaws found in sea urchins. Heart Urchins live in burrows that they build just under the surface of the sea and they circulate water via a band of special tiny spines called fasciole. They consume edible bits found in the sand as the burrow including plants and small invertebrates. They have two sexes and reproduce via external fertilization releasing eggs and sperm simultaneously into the water. They are preyed upon by Helmet Shells (Cassidae). Heart Urchins have never been an important item of human commerce.