{"id":26999,"date":"2023-04-06T15:45:24","date_gmt":"2023-04-06T13:45:24","guid":{"rendered":"https:\/\/www.discoverwildlife.com\/?p=7191"},"modified":"2023-04-06T16:35:46","modified_gmt":"2023-04-06T14:35:46","slug":"what-are-sea-urchins-a-guide-to-the-fascinating-and-strange-creature-that-inhabits-the-sea-bed","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcwildlife\/rss_feed\/what-are-sea-urchins-a-guide-to-the-fascinating-and-strange-creature-that-inhabits-the-sea-bed\/","title":{"rendered":"What are sea urchins? A guide to the fascinating and strange creature that inhabits the sea bed"},"content":{"rendered":"

We take a look at the fascinating sea urchin <\/p>

By Dr Amy-Jane Beer\n \t\t<\/p>

Published: Thursday, 06 April 2023 at 12:00 am<\/p>

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What are sea urchins?<\/h2>\n

A confession: I have a soft spot for the sea urchin, an echinoderm in the class Echinoidea. In life it contained a coil of gut, a five-toothed feeding apparatus known resplendently as Aristotle\u2019s lantern, and a radiating system of nerves and hydraulic canals. Oh \u2013 and gonads. In fact at this time of year, urchins are mostly gonad.<\/p>\n

The test bears the five-way symmetry that hallmarks most echinoderms, the spiny-skinned group that also includes starfish<\/a><\/strong> and sea cucumbers. Look closer and you\u2019ll see double rows of pores where the hydraulic tube feet protruded, each one ending in a tiny sucker that helps attach the urchin to the seafloor, passes food to the mouth and arranges adornments of gravel, shell and weed as camouflage.<\/span><\/p>\n

Between the pores are white bumps, or tubercles, the \u2018ball\u2019 part of ball-and-socket joints where individual spines were attached. Each spine would have been able to swivel, in defence or to wedge the body in a crevice.<\/span><\/p>\n

If you find a live urchin and look closer still (a hand lens will help, or use your binoculars backwards), you\u2019ll see a third kind of appendage. These are globiferous pedicellariae, as delicate as their name is clumsy. Each tiny pincer-like structure, mounted on a slender stalk, can deliver a minute jab of toxin. You might feel these stings when handling a live urchin, but generally our skin is too thick to be troubled by them.<\/p>\n

The test is made up of hundreds of plates, which grow slowly from the edges. Empty tests often break along the joints; if so, take comfort knowing that the former occupant was probably healthy. Loose joints indicate active growth was taking place, while the plates of a starving urchin become welded together.<\/p>\n

Dr Amy-Jane Beer6<\/p>\n