Fire urchin

Care at a glance

Overview

Peaceful toward fish, but not reef safe and not a beginner's animal. It eats coral polyps and encrusting invertebrates, it is venomous enough to send a careless keeper to bed for a day, and it needs a very large, mature fish-only or rubble tank. Feed dried seaweed, sinking pellets, and bits of shellfish at night, drip acclimate it very slowly, keep nitrate low, and never use copper. Move it only with a container, and keep triggers and large wrasses away from it.

In the wild

The fire urchin lives on sand and rubble slopes and coral bottoms across the Indo-Pacific, from the eastern Indian Ocean to Japan, the Philippines, and New Caledonia, from shallow water down to about 170 m. It hides in caves by day and roams in the open at night. It grows to dinner plate size, so a tank of 760 liters or more with a wide sand floor and locked rock is the minimum. Fine sand matters because the soft body and tube feet tear on sharp rubble, and the water stays at 22 to 27 C with pH 8.1 to 8.4.

Good to know

Asthenosoma varium belongs to the Echinothuriidae, the leather urchins, whose test plates overlap like roof tiles instead of fusing, so the animal is flexible and sags when lifted. It reaches about 25 cm across in red, orange, purple, and white. Each short spine carries a bright blue or white capsule near the tip filled with venom that works like a hypodermic syringe, and a sting brings hours of severe pain. It hosts the Coleman shrimp (Periclimenes colemani), the shrimp Allopontonia brockii, and the zebra crab Zebrida adamsii, which live among the spines. It is an omnivore that eats algal film, sponges, tunicates, coral polyps, and detritus.

Common questions

Related species

• 

  Long-spine urchin

  Diadema setosum

  9.8 in (25 cm) · 50 gal (190 L)

  9.8 in (25 cm)50 gal (190 L)72–79°F (22–26°C)

• 

  Blue linckia star

  Linckia laevigata

  11.8 in (30 cm) · 53 gal (200 L)

  11.8 in (30 cm)53 gal (200 L)75–81°F (24–27°C)

• 

  Chocolate chip star

  Protoreaster nodosus

  11.8 in (30 cm) · 53 gal (200 L)

  11.8 in (30 cm)53 gal (200 L)75–81°F (24–27°C)

• 

  Red knob sea star

  Protoreaster linckii

  11.8 in (30 cm) · 53 gal (200 L)

  11.8 in (30 cm)53 gal (200 L)75–81°F (24–27°C)

• 

  Wedge sea hare

  Dolabella auricularia

  11.8 in (30 cm) · 50 gal (190 L)

  11.8 in (30 cm)50 gal (190 L)75–81°F (24–27°C)

• 

  Blue spot urchin

  Astropyga radiata

  7.9 in (20 cm) · 100 gal (380 L)

  7.9 in (20 cm)100 gal (380 L)72–82°F (22–28°C)