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
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

Peaceful toward fish and mostly an algae grazer, but this is a venomous animal that can put its keeper in hospital, and it does not belong in a home tank. If one is kept anyway, it goes in a large fish-only or rubble tank, is never touched with bare hands, is moved with a container, and children never have access. It is a reef caution because it picks up and carries off frags and shells for cover and will graze coralline and film algae bare. Feed dried seaweed, keep nitrate low, drip acclimate slowly, and never use copper. Triggers and large wrasses will attack it.

In the wild

The flower urchin lives on coral rubble, rock, sand, and seagrass beds from the Red Sea and East Africa across to Okinawa, Australia, and the Cook Islands, from the tide line down to about 90 m. It covers itself with shells, rubble, and weed and sits in the open by day. In a tank it needs 380 liters or more, a mature system with plenty of algae, and a layout where you never have to reach past it. Water stays at 22 to 28 C with pH 8.1 to 8.4.

Good to know

Toxopneustes pileolus is a regular urchin in the family Toxopneustidae, a relative of the collector urchin. The test reaches about 15 cm across, sometimes cited to 20 cm, with short spines almost hidden under hundreds of large pedicellariae that open like pink or white flowers with a purple centre. Those flowers are the danger: each has three fanged jaws that grip skin and inject venom (Contractin A and peditoxin), causing intense pain, muscle weakness, numbness of the lips and tongue, and in recorded cases temporary paralysis and trouble breathing. It is listed by Guinness World Records as the most dangerous sea urchin. In the wild it eats algae, bryozoans, and detritus.

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 that lasted about six hours.

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.

How big does a Flower urchin get?

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

Related species