Collector Urchins - small spines, large pincers

DLNR image - basket o urchins

Just a short entry this week on one of the animals in our observation tank, the Collector urchin, Tripneustes gratilla or hāwa 'e maoli. You all probably know of their use in controlling the invasive seaweeds (DLNR Press Release with lots of great pictures) and most folks appreciate their lack of long venomous spines (like the wana or diadem urchins). We also tend to appreciate their propensity for collecting bits of substrate and holding it with their suction tube feet. These items may serve as ballast, camouflage, food, or more.

But the other thing folks notice about them are the beautiful purple bands between the spines. These bands are actually rows of tiny pincers known as pedicillaria (image below). It is hard to believe that tiny rows of these cover the urchins body, but take a close look sometime and you can see them.

Pedicillaria  - more images from the blog below.
Image Livington, Copyright BIODAC

They are unable to pierce our skin or cause much issue for us - however they can be used to discourage settlement of small creatures on the urchin and perhaps other uses as well. A relative of the collector urchin, the flower urchin, Toxopnuestes pileolus actually has some rather serious venom associated with the pincers. For some entertaining readings on this and other seastar/sea cucumber/sea urchin toxicity,  check out this article on Echinoderm Envenomation.

For a very nice blog on the pincers themselves, I suggest you go to Jim Lemire's site, "From Archaea to Zeaxanthol - DNA, Darwin, and a bottle of rum...not necessarily in that order" for the article Weekly Urchin: Pedicillaria. He explains why urchins are cooler than the snail group.

Aloha,

Mark