A Few Sea Urchin Facts You May Not Know
Sea urchin facts can be quite interesting. That’s because sea urchins are colorful underwater creatures who are members of the echinoderm family. The family includes such other animals as sea cucumbers, sea stars, crinoids, and brittle stars.
Sea urchins have five-point symmetry and move with tube feet. Their body colors can range from red or green to purple, brown or olive. Sea urchin facts tell us that the name “urchin” comes from an old name for hedgehogs. Apparently someone thought that sea urchins looked like the relatives of spiny hedgehogs.
What do sea urchins look like?
Sea urchins can range from around 2-½ inches long to over 4-½ inches long. There is one species of urchins which can grow to be approximately fourteen inches long. The five-section bodies are very unique with each part being identical in size. They are not like their relatives, the sand dollars who, although flat, have both front and rear ends.
According to sea urchin facts, it is the bottom half of the urchin’s body which contains the mouth. Around the mouth are soft lips. There are five pairs of tube feet and five pairs of gills. Opposite the mouth, on the upper half of the body is the anus. A section of hard plates surrounds the anus and these are known as the periproct.
Sea urchins do not have muscles, but instead they develop spines, the sharp, pointed bones that make up the endoskeleton of urchins. While the spines are painful should you be wounded by one, there is no long-lasting damage or poisons to avoid. One particular sea urchin, diadema antillarum, lives in the Caribbean, and can have a sharp spine which grows up to four inches long. You definitely wouldn’t want to step on one of these underwater creatures.
Sea urchin reproduction
Sea urchin facts also indicate that there are both males and females with testicles and ovaries, respectively, as in other species. Sea urchins release their sperm and eggs into the sea where they are united with one another. Once an egg is fertilized, an embryo can be formed in as small an amount of time as four hours.
The sea urchin starts out as nothing more than a ball of cells and then it turns into larva which is shaped like a cone. The larva has arms covered with cilia (which look like threads or hairs) which catch food (algae and invertebrates) and push it into the mouth. It can take many months for the larva to become an adult sea urchin.
From larvae to adulthood
When it is time, the larva goes to the bottom of the ocean and an adult can appear in as little as an hour for some species. Others take many months to shift from larval to adult form. Everything having to do with sea urchins develops in fives. For example, in addition to their five body parts, they also have five teeth. Their stomach has five parts as well.
Among sea urchin facts are the specifics of their vascular system. They have a water vascular system and a hemal system, which contains blood. Sea urchins also have five pair of gills which are placed around the mouth. These allow the urchin to breathe as do their tube feet which are also part of the sea urchin’s respiratory system. They do not have a brain, but sea urchins do have five nerves which surround the mouth and can radiate feeling through other parts of the body. A sea urchin is sensitive to light, touch and certain chemicals.
Parts of sea urchins are eaten y humans in many parts of the world. The ovaries, known as roe, are considered delicacies. Some species are eaten raw. Japan, where urchins are considered a delicacy, is the largest importer of sea urchins.