Sea urchin
Sea Urchin
Sea urchin (/siː ˈɜːrʃɪn/), from the Old English 'eorcyn', is a common name for a group of marine animals that belong to the class Echinoidea of the phylum Echinodermata. They are characterized by their spiny, globular bodies and are found in oceans worldwide.
Etymology
The term "sea urchin" is derived from the Old English 'eorcyn', which means 'hedgehog'. This is due to the similar appearance of sea urchins to hedgehogs, with their spiny exteriors.
Anatomy
Sea urchins have a hard, calcareous shell called a test, which is covered in spines. The test is divided into five equal sections, each containing a pair of tube feet. These tube feet are used for locomotion and feeding. The mouth of the sea urchin, known as the Aristotle's lantern, is located on the underside of the body and is used for grazing on algae and other organic matter.
Reproduction
Sea urchins reproduce through a process known as broadcast spawning, where both males and females release their gametes into the water column. Fertilization occurs externally, and the resulting larvae, known as pluteus larvae, are planktonic.
Ecology
Sea urchins play a crucial role in their ecosystems. They are important grazers and can significantly influence the distribution and abundance of algae. Some species of sea urchins, such as the purple sea urchin, are also known to form urchin barrens, areas devoid of macroalgae due to overgrazing.
Related Terms
- Echinoidea: The class to which sea urchins belong.
- Echinodermata: The phylum to which sea urchins belong.
- Test (biology): The hard, calcareous shell of a sea urchin.
- Tube feet: Small, suction-cup like appendages used by sea urchins for locomotion and feeding.
- Aristotle's lantern: The mouth of a sea urchin.
- Broadcast spawning: A method of reproduction used by sea urchins.
- Pluteus larvae: The larval stage of sea urchins.
- Urchin barrens: Areas devoid of macroalgae due to overgrazing by sea urchins.
External links
- Medical encyclopedia article on Sea urchin
- Wikipedia's article - Sea urchin
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