This is the second installment in our series introducing how to properly observe creatures in the "Tide Pool" Tokyo Sea Life Park we're focusing on the "Purple Sea Urchin."

・First observation of "tide pools" "Are chitons hard or soft?"

Purple Sea Urchin is distributed in the warm seas from Honshu to Kyushu, inhabiting rocky areas from the intertidal zone to depths of about 70 meters. It has a round, dark purple body with spines that are about the same length as its body. Including the spines, large specimens can reach a diameter of about 15 centimeters.

If you look closely at the body of Purple Sea Urchin, you'll see many thin, dark purple, thread-like structures swaying between its spines. These are called tube feet, the urchin's legs. The slightly swollen tip acts like a suction cup, allowing it to firmly attach itself to surfaces.

When you look at sea urchins inside holes in rocks, you'll see them nestled snugly, their thick spines spread out. Normally, their spines would get caught in the opening of the hole, preventing them from going in or out. However, sea urchins can move their spines, allowing them to freely pass through such holes and crevices.
In this way, Purple Sea Urchin moves by using its many tube feet and spines in an orderly fashion.

By skillfully touching Purple Sea Urchin, you can feel the movement of its spines with your fingers. If you carefully insert one finger between the spines, paying attention to the tips, the sea urchin will move its spines and touch your finger. It seems to be using its spines, its weapon, to keep you from getting any closer.

In the "Tide Pool" aquarium, there is a "one-finger rule" where you gently touch the creatures with just one finger. This method of touching is not only to avoid harming the creatures, but is also very useful for understanding their individual characteristics.

Also, during the "Tide Pool" animal demonstration (1:30 PM to 3:00 PM), you can touch sea urchin shells. The spines have fallen off, but you can see the neatly arranged bumps of various sizes. The spines are connected to these bumps by a joint-like mechanism, allowing them to move freely. If you look closely at the shell, you can learn about the structure of the sea urchin's body. Feel free to ask the staff and enjoy observing them while comparing them to live Purple Sea Urchin.

Photo above: Touching a sea urchin
Photo: Spines and tube feet
Photo below: Sea urchin shell

[Tokyo Sea Life Park]

(June 1, 2012)