Long-Spine Urchin

Care at a glance

Overview

A large nocturnal grazer best kept singly in bigger reef and fish-only systems. Peaceful toward tankmates but its long venomous spines are a hazard to careless hands and to fish that blunder into them. Drip acclimate slowly, as it is intolerant of sudden salinity, pH, or oxygen swings.

In the wild

A powerhouse algae grazer of Indo-Pacific reefs, hiding in crevices by day and roaming to scrape algae at night. It needs a large, mature tank with open grazing surfaces and enough rock to shelter under. Because the whole animal including spines can span 25 cm or more, it wants real swimming and grazing room rather than a nano.

Good to know

Diadema setosum belongs to the family Diadematidae. Its extremely long, thin, hollow spines are venomous and brittle, breaking off in skin and delivering a painful sting, so it must be handled with care during acclimation and rockwork. It is an efficient herbivore that controls turf and film algae, and in the wild Diadema are keystone grazers that keep reefs from being smothered by algae.

Did you know

Its needle-like spines can pivot toward a shadow passing overhead, and many species carry a photoreceptive ring that helps the whole urchin behave like a crude compound eye.

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