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Species Profile – Pencil Urchins

November 16, 2010
Large Pencil Urchin caught in the dive at Pourtales Terrace

Large Pencil Urchin: Photo by Mike Dunn

On our dive at Pourtales Terrace we came across some enormous Pencil Urchins, so named because they have thicker spines than most. These belong to a group of primitive sea urchins characterized by their primary spines being much more widely separated than in other sea urchins. Sea urchins are members of the phylum Echinodermata (spiny skin) that also includes sea stars (or star fish), sea cucumbers, brittle stars, and crinoids.  Like other echinoderms, sea urchins have five-part symmetry — they have roughly spherical bodies with five equally sized parts radiating out from the central axis. The internal organs are enclosed in a hard roundish housing known as a test made of fused plates of calcium carbonate. Urchins use their prominent spines for defense and for locomotion, while their tube feet are used primarily for grasping the substrate and manipulating of larger particles.

Aristotle's lantern, the five plates that form the mouth parts of a sea urchin.

Aristotle's lantern, the five plates that form the mouth parts of a sea urchin: Photo by Mike Dunn

The mouth of most sea urchins is located on the underside of the animal and is made up of five calcium carbonate teeth or jaws, with a fleshy tongue-like structure within. Urchins feed by using their jaws and tongue to rasp encrusting organisms or algae off of hard substrates. The entire chewing organ is known as Aristotle’s lantern. It looks like something from a sci-fi film that you would not want to see coming at you in a narrow passageway. It also reminds me of the jaws you see on the back of landscaping trucks that are used to transplant large tree saplings.

We pulled up what looked to me like two different species of urchins: one small and a couple of very large specimens. The test of the largest is the size of a baseball and the spines are about 8+ inches long. The spines look like they are made of wood — so much so that I would have named this urchin  the “skewer urchin” or the “toothpicks-for-giants urchin.” Most of the scientists said they had not seen this particular species before or ones this large. A close look at the larger urchins revealed intricate details of their anatomy — they look like something designed for futuristic warfare with multiple layers of movable plates to protect them as they lumber across the landscape devastating everything in their path with the swipe of their spines.

The mystery case maker used sand grains and shell bits to make tubular cases.

Closeup of a mystery case: Photo by Mike Dunn

The smaller urchin had several things attached to its spines. Some looked like deep-sea equivalents of caddisfly tubes with pieces of sand and shell cemented together to house some unknown invertebrate. The scientists I spoke to aren’t sure who the case makers are. A mystery to be solved by another researcher perhaps when images or specimens from this cruise are further analyzed back on land.

This small urchin has several mystery cases attached to its spines.

This small urchin has several mystery cases attached to its spines: Photo by Art Howard

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2 Comments leave one →
  1. Liz Baird permalink
    November 17, 2010 12:34 am

    Excellent echinoderms!
    Have you seen any sea cucumbers?

    • ncmuseummike permalink
      November 17, 2010 2:20 am

      Yes, a cool one was collected. I’ll try to post a couple of pics soon (internet willing – the official slogan of this cruise:)

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