Sea Urchins

Lone Purple sea star
Purple sea stars in bottom of pool Sea stars have a hard test or shell. This is what many visitors find in tidepools Lots of sea urchins living in pool Sea urchins lying along cracks in bottom of pool Sea urchins will stay in the same pool for long periods of time and sometimes their whole life Lots of sea urchins living in pool

Purple Sea Urchin (Strongylocentrotus purpuratus)

The purple sea urchin is the most common sea urchin visitors will see in the tidepool. They have an unmistakable purple color. They are covered by hundreds of spines and tube feet. They are typically a few inches in width an found in pools of water. They prefer to be submerged all the time but on occasion will be caught above water as the tide reseeds.
Red urchin with smaller purple urchins
Deep red colored urchin with smaller purple urchins

Red Sea Urchin (Strongylocentrotus franciscanus)

Red sea urchins range in color from a strong red to a very dark red almost black color. They are a little larger than the purple sea urchins and found in the deeper parts of pools. They are not very common so find one can be tricky. They feed on algae similar to the purple sea urchins.

White Sea Urchin (Lytechinus anamesus)

White sea urchins prefer deeper and cooler waters. Adults appear light brown with white and brownish spines. They are not as common as the purple sea urchins and not quite as large. They feed on algae and diatoms.
Description – Sea urchins are very unique animals in that their bodies are covered with spines. The spines serve multiple purposes including protection, feeding and making a home. Urchins have a hard outer shell called a teste. Spines are attached to the test along with tube feet. Urchins like sea stars have many tube feet that they use for feeding and moving. The spines are different lengths. Contrary to popular believe, they do not have an venom in the spines.

Feeding – Urchins are herbivores and primarily eat brown algae. They will spend most of their lives sitting on the bottom of the ocean or pool waiting for algae to get caught on the top of their spines. The urchins, using their tube feet will move the algae from the top of their shells to the bottom where the mouth is located.

Protection – The spines of an Urchin are the most obvious form of protection. They prevent the smaller and sometimes larger animals from preying on them. Urchins also have a hard shell that spines are attached to that also help protecting the animals.

Ecology – Urchins will spend most all of their time sitting on the ocean floor or bottom of a tidepool. They sometimes create a home scar that is a small depression in the rocks. The home scar is created slowly over time as the urchin will move around on the same spot and the spines slowly erode the rock. Urchin also can venture out away from their home scar or preferred location when food becomes scares. Urchins have been known to migrate in mass and look for additional food sources. During this movement, they can devour most all plant live in the area.
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