TankBud

Flower urchin

Toxopneustes pileolus

Also known as Flower sea urchin, Rappa uni

SaltwaterInvertebrate

Flower urchin (Toxopneustes pileolus)
Diego Delso · CC BY-SA 4.0

Care at a glance

Temperature
72–82°F
22–28°C
pH
8.1–8.4
Adult size
5.9 in
15 cm
Minimum tank
100 gal
380 L
Temperament
Peaceful
Social behavior
Solitary
Tankmates
With caution
Swim level
Bottom
Diet
Omnivore
Difficulty
Difficult
Breeding
No record
Rarity
Very rare
Reef safe
Reef safe with caution
Family
Toxopneustidae
Origin
Indo-West Pacific reefs, seagrass and rubble, Red Sea to Japan and Australia

Overview

The flower urchin is a peaceful algae grazer, but its venom can put a keeper in the hospital. It does not belong in a home tank, and it is for experienced keepers only.

Did you know

In 1930 the Japanese biologist Tsutomu Fujiwara let a flower urchin sting his finger on purpose and wrote up the result. Seven or eight pedicellariae caused severe pain, faintness and paralysis of his lips, tongue and face. The effects lasted about six hours.

Caring for the flower urchin

Never touch a flower urchin with bare hands, and move it only with a container. Make sure children never have access to its tank.

It needs a large fish-only or rubble tank of at least 100 gal (380 L). Use a mature system with plenty of algae, and a layout where you never have to reach past it. Keep the water at 72 to 82°F (22 to 28°C) with a pH of 8.1 to 8.4, and hold nitrate low. Drip acclimate it slowly, and never use copper.

It is mostly an algae grazer and will graze coralline and film algae bare. In the wild it also eats bryozoans and detritus. Feed it dried seaweed.

The flower urchin is peaceful toward fish, but triggers and large wrasses will attack it. It is a reef caution, because it picks up and carries off frags and shells for cover.

Good to know

The flower urchin, Toxopneustes pileolus, is a regular urchin in the family Toxopneustidae and a relative of the collector urchin. Its test is sometimes cited at up to 20 cm across. Its short spines are almost hidden under hundreds of large pedicellariae that open like pink or white flowers with a purple center. Those flowers are the danger. Each has three fanged jaws that grip skin and inject venom, Contractin A and peditoxin. The venom causes intense pain, muscle weakness and numbness of the lips and tongue, and in recorded cases temporary paralysis and trouble breathing. Guinness World Records lists it as the most dangerous sea urchin.

In the wild

The flower urchin lives on coral rubble, rock, sand and seagrass beds, from the tide line down to about 90 m. Its range runs from the Red Sea and East Africa across to Okinawa, Australia and the Cook Islands. It covers itself with shells, rubble and weed and sits in the open by day.

Common questions

What size tank does a flower urchin need?

A flower urchin needs at least 100 gal (380 L). It spends most of its time in the bottom.

What temperature and pH does a flower urchin need?

A flower urchin is comfortable at 72–82°F (22–28°C) with a pH of 8.1–8.4.

What does a flower urchin eat?

A flower urchin is mostly an algae grazer and will graze coralline and film algae bare. In the wild it also eats bryozoans and detritus, and in the tank it takes dried seaweed.

How big does a flower urchin get?

An adult flower urchin reaches about 5.9 in (15 cm).

Related species