Eucidaris tribuloides

Identification: the spherical test is up to 6 cm across. The few primary spines are very thick, sometimes banded with a paler colour, and set in five double rows on large tubercles; they are blunt-tipped and lack an epithelium, so algae and coralline algae settle on them. The test is protected by small, flat, off-white secondary spines edged in orange-brown, and the top carries a broad pale orange disc. It closely resembles the Pacific Eucidaris thouarsii and Stylocidaris affinis. It belongs to the Cidaroida, a basal order much studied in developmental biology.

In the wild it lives in the western Atlantic from Cape Hatteras (North Carolina) to Rio de Janeiro, throughout the Caribbean and the Gulf of Mexico; a related form, E. t. africana, occurs in Cape Verde, the Gulf of Guinea, the Azores and Ascension Island. It reached Malta in 1998, probably in ballast water. It lives on reefs, seagrass beds and rocky bottoms from 0 to 50 m, in reef crevices and back-reef lagoons. By day it anchors itself in a cavity with its spines and rarely strays far; at night it feeds mainly on corals and sponges according to Wikipedia, and also grazes algae, carrion, cnidarians and molluscs. As they age, its spines become porous and shelter small gastropods.

Reproduction: the sexes are separate and gametes are released into the water. Breeding follows seasonal and lunar cycles: in Florida females are most gravid in late summer and early autumn; in Panama from spring to autumn, peaking around the full moon.

Status: it has not been evaluated by the IUCN and is not CITES-listed. It is not eaten, but it is commonly collected for the aquarium trade.