Meoma ventricosa

Lore & Background

The red heart urchin has a somewhat flattened, heart-shaped test made of closely fitting calcium carbonate plates, covered by short, dense, movable spines on small tubercles. The test is dark reddish-brown and the spines a little paler. Although it has pentagonal radial symmetry, it also has bilateral symmetry because one interambulacral area is undeveloped, leaving only four apparent. The mouth is on the oral surface near the anterior end and the anus at the posterior end.

It inhabits reef flats, turtle grass beds, areas of coral fragments, and deep reefs in the Caribbean Sea, the Bahamas, Florida, and Bermuda. It buries itself in sedimentary areas with sand, silt, or coarse coral rubble. The urchin feeds by swallowing sediment coated with films of algae and bacteria; fifty-six tube feet near the mouth form a disc that uses mucus to adhere sand particles, which are then retracted into the mouth. Growth is slow, limited by organic material and oxygen in the sediment. Adults often emerge onto the seabed at night and reburrow by day, while juveniles remain permanently buried.

Predators include stingrays, other fish, loggerhead turtles, and the sea star Oreaster reticulatus. The urchin can emit a noxious yellow exudate that repels fish. In 1997, an epizootic off Curaçao caused by the bacterium Pseudoalteromonas led to spine loss and death, possibly linked to polluted water. Breeding occurs in Florida between August and February, with planktonic larvae settling on sandy seabeds. Most adults host the parasitic crab Dissodactylus primitivus, usually near the mouth.

Reader's Guide

The red heart urchin is significant for its ecological role in sediment disturbance: during feeding, it increases water content and decreases sediment density, which may boost the growth of algae and bacteria that form its food films. This impact on the microhabitat is considerable. Its slow growth rate is tied to the limited organic material and oxygen in sediment, especially at night, which drives its nocturnal emergence behavior. The 1997 epizootic event off Curaçao highlights its vulnerability to bacterial disease linked to environmental pollution, as the bacterium Pseudoalteromonas caused spine loss and mortality in a localized area down-current from a harbor. The species also serves as a host for the parasitic crab Dissodactylus primitivus, a common relationship among adults. Its dual symmetry—combining pentagonal radial and bilateral features—makes it a notable example of morphological adaptation in echinoids, resembling sand dollars. The urchin's burrowing rate of 3 to 6 centimeters per hour by day, doubling at night, and its ability to leave depressed trails and mounds, further underscore its role as a bioturbator in Caribbean sedimentary environments.

Did You Know?

• The red heart urchin can reach a diameter of 20 centimeters.
• It has both pentagonal radial symmetry and bilateral symmetry, with two of five sections merged more closely.
• It burrows at 3 to 6 centimeters per hour during the day and twice as fast at night.