A round urchin to 15 cm (6 in) with short blunt spines, almost always wearing something: seagrass blades, shell fragments, bits of rubble held over the back by its tube feet. The habit is what the name records, and the animal collects continuously.
Why it does it is not fully settled. The load shades the urchin from ultraviolet light, breaks up its outline, and may weigh it down against surge; individuals in bright shallow water carry more than those in the shade, which supports the sunshade explanation over the others.
The spines are short and hollow and carry mild venom, along with small pincer organs between them that grip and inject anything soft that lands on the test. Stepping on one is unpleasant rather than dangerous, but the spine tips break off in the skin.
It is one of the most important grazers on any reef flat. Where these urchins are removed, algae take over the seagrass and rubble within months, and they are farmed and released as a biological control on algae in several countries - an animal whose main value is that it eats constantly and indiscriminately.
- short blunt white to purple spines over a dark test, never long needles
- usually carrying seagrass blades, shells and rubbish on its back
- bands of tube feet visible between the spines
- up to 15 cm across
