Habitat: Grassy areas with sand bottoms, reefs, and among rocks and rubble. Distribution: Panama, Caribbean. Natural History Notes: T. ventricosus is able to grasp tightly to substate, enabling it to live in high-energy habitats such as reef-crest bedrock and on Sargassum. It often co-occurs with L. variegatus. In Panama, the species remains ripe throughout the year, and spawning occurs at random during the lunar cycle. The cryptically colored shrimp Gnathophyllooides mineri Schmitt lives among the spines, near the mouth, and feeds on the epidermis of the spines. Protozoan parasites have also been reported. Depth: 0-55m Characteristics: The urchin is large, with a test diameter of up to 150mm. The test is hemispherical, with ambulacral pores in three vertical series, and numerous small tubercles. The tissue around the jaws is dark brown.