Long Spined Urchin
Diadema antillarum
To 55 cm from arm tip to arm tip (some reports to 95cm).

Adults: Numerous long, thin spines. Black, rarely white.
Juveniles: Spines may be banded black and white. Body with some white spots.

Regularly form aggregations along rocky shorelines, seagrass beds and coral reefs, typically sheltering during the day then grazing at night. This species usually lives at 1-20m (3-60ft). They will often lodge themselves in a crevice, so that only their spines can be seen, but individual urchins who can't find a suitable crevice will live in more exposed situations. Individuals that have been able to find a crevice usually will roam about one metre from their crevice at night during feeding. Diadema is very sensitive to light, and will often pick its crevice or resting place based on how much shade there is. Diadema mostly eat algae, young corals, zoanthids and sometimes seagrass. Starving urchins have been known to become carnivorous.

The mucous coating of the spines, normally used to kill organisms that live in the spines, carries a mild poison that also aids in deterring smaller predators.

In 1983 to 1984,  Diadema antillarum underwent mass mortality, thought to be due to a water-borne pathogen that has not yet been identified, with more than 97% of the population dying. This led to some Antiguan reefs became overgrown by macroalgae. This inhibits coral growth and has further compounded the ongoing decline of scleractinian corals. It also had an overall negative effect on coral reef resilience, which encompasses the ability of a system to resist and recover from changes stemming from perturbation events. In Antigua there has been a comeback of Diadema.

Life Cycle
The spawning of D. antillarum appears to be connected to the lunar calendar. During the summer season, the egg and sperm are released once during each lunar month. In the fertilization process, male and female urchins secrete pheromones to alert other urchins to respond by releasing their eggs and sperm in mass reproduction, where they are fertilized and develop into the larval echinopluteus. These larvae migrate into the upper surface waters and have long ciliated arms that they use to capture the phytoplankton on which they feed. Their arms are supported by slender calcite rods. After several weeks of living and feeding in the plankton a cluster of cells in the lower left-hand side of the body start to differentiate rapidly. This is the rudiment and it is these cells that give rise to the adult sea urchin. As the rudiment develops, adult features, such as tube-feet, begin to appear, while larval structures, including the arms and even the larval gut and mouth, are resorbed and eventually lost. The newly metamorphosed juvenile sinks to the sea floor to begin life as a benthic adult.
    Ecological Descriptors
Habitat Size (cm) Diet Behaviour Sex 
Co, R, S
Veg (Co) Noct I F
Black Sea Urchin
Lime Sea Urchin
Longspined Sea urchin
Longspined Sea urchin