Purple Urchin

Arbacia punctulata

Also known as Atlantic Purple Sea Urchin, Purple-spined Sea Urchin

SaltwaterInvertebrate

Purple Urchin (Arbacia punctulata) — NOAA · Public domain

Care at a glance

Temperature: 68–81°F (20–27°C)
pH: 8.1–8.4
Adult size: 3.1 in (8 cm)
Minimum tank: 20 gal (75 L)
Temperament: Peaceful
Social behavior: Solitary
Swim level: Bottom
Difficulty: Easy
Breeding: Hard
Rarity: Common
Reef safe: Reef safe with caution
Origin: Western Atlantic, from New England to the Caribbean and Gulf of Mexico
Family: Arbaciidae

Overview

A hardy, tireless grazer that strips nuisance algae, but it does not stop there: coralline gets rasped away, loose frags get bulldozed or carried off, and sessile invertebrates may get sampled. It suits fish-only systems and rough-and-ready reef tanks where that appetite is an asset rather than a risk. Feed nori once the natural algae is gone.

In the wild

Native to the western Atlantic from New England down to the Caribbean and the Gulf of Mexico, on shallow rocky, sandy, and shelly bottoms. In the aquarium it wants sturdy, well-stacked rockwork, because it will shoulder straight through anything loosely placed.

Good to know

Arbacia punctulata is a dark, purple-spined urchin in the family Arbaciidae that reaches about 8 cm across. Unlike most cleanup crew urchins it is a true omnivore, grazing algae but also willing to eat sponges, bryozoans, and other sessile animals.

Did you know

This species has been a workhorse of biology labs for over a century, and classic discoveries about fertilization and cell division were made using its eggs.