Sea Urchin Facts Vol.2

Some more fun facts about sea urchins, you can see my first post here. (image: staroftheeast on instagram)

Regular sea urchins have a five-fold symmetry which you can see most clearly in the pink ones, they are born as bilateral symmetric but develop five-fold symmetry as they mature.
However sand dollars are also sea urchins and they are called irregular sea urchins as they are often oval and radial symmetric.

The bodies of adult sand dollars, display radial symmetry. The petal-like pattern in sand dollars consists of five paired rows of pores. The pores are perforations in the endoskeleton through which podia for gas exchange project from the body. The mouth of the sand dollar is located on the bottom of its body at the center of the petal-like pattern.

(image: staroftheeast on instagram)

Unlike other urchins, the bodies of sand dollars also display secondary front-to-back bilateral symmetry. The anus of sand dollars is located at the back rather than at the top as in most urchins, with many more bilateral features appearing in some species. These result from the adaptation of sand dollars, in the course of their evolution, from creatures that originally lived their lives on top of the seabed to creatures that burrow beneath it. (source: wikipedia)

Sea urchins are omnivorous animals and therefore eat both plant and animal matter. The sea urchin mainly feeds on algae on the coral and rocks, along with decomposing matter such as dead fish, mussels, sponges ans barnacles.

Sea urchins' tube feet arise from the five ambulacral grooves. Tube feet are moved by a water vascular system, which works through hydraulic pressure, allowing the sea urchin to pump water into and out of the tube feet, enabling it to move. (image source: wikipedia)

The Phyllacanthus imperialis sea urchin, more commonly known as the Sputnik urchin have thick spines which leave a very different texture once they die and have no spines left. Around the big spines are tiny spines for more protection. (image source: galleryofinvertebrates)
We find them very seldom on our beaches here, but when we do we use them for some special jewelry:

Sterling silver Sea urchin earrings available here.

Brass and Enamel Sputnik sea urchin cuff available here.

Here you can see a sea urchin in action, it is pretty amazing!

Sea Urchin Facts

I thought it would be fun to investigate more about sea urchins and share my findings with you. I tried to find out how many species of sea urchins are out there and different sources give different amount, I think the exact amount is not known as still new sorts are discovered, but it must be between the 700 and 900 types of sea urchins! (Source of Sea urchin Anatomy image: Abiogenisis)

Their anatomy is very unique. They don't have any brains but do react to touch and light. Their mouth is under the body (the part which has a large hole when you find them on the beach) and their anus is on top (the little hole). Their teeth, called Aristotles Lanterns are intriguing little things, their teeth sharpen themselves and renew every so often.

When we find sea urchins on the beach (we never collect living ones from the sea) they are often cleaned up by the sun and the waves. But we very often find them with their spines too which is a painful thing to clean, but when they have still their spines it often means that they haven't been on the beach for long and they still have their teeth inside. We carefully take them out and offer them in our supply shop as they are loved materials for sailors valentines art works as you can see below.

Sailor's Valentines are little framed art pieces made entirely out of sea treasures, usually very small treasures are used making them look like fine mosaic pieces. There are collectors of them, Antique ones are rare and not many people make them today. (Source of Sailor's Valentines image: Valentinesmansion).

The sea urchin above is the Heterocentrotus species Slate pencil sea urchin, image from ryanphotographic. We sometimes have necklaces of their spines in our shop.

Here is a necklace made with a Slate pencil Urchin Spine, available in our shop,

This striking striped spined sea urchin is the Echinothrix diadema Sea urchin (image from ryanphotographic).

They make striking earrings, available in our shop.

The sea urchin's name comes from hedgehog as urchin is the old name for hedgehog so they are hedgehogs of the sea.

I will be digging up more sea urchin facts for more blogposts but for now, here are 10 fun facts about sea urchins: