Sea urchin
Sea urchins are spiny, globular echinoderms found in all oceans.
They typically have a globular body covered by spiny protective tests, ranging from 3 to 10 cm across, and move slowly using tube feet and spines. They feed primarily on algae but also on slow-moving or sessile animals, and their predators include sharks, sea otters, starfish, wolf eels, triggerfish, and humans. Sea urchins have been studied since the 19th century as model organisms in developmental biology due to their easily observable embryos, and their genomes continue to be studied because of their unusual fivefold symmetry and relationship to chordates.
- Class
- Echinoidea
- Size range
- 3 to 10 cm (1 to 4 in), largest up to 36 cm (14 in)
- Habitat
- All oceans, intertidal zone to hadal zone depths
- Diet
- Primarily algae, also slow-moving or sessile animals
- Known for
- Model organisms in developmental biology; fivefold symmetry; fossil urchins used as amulets
Lore & Background
Sea urchins are members of the phylum Echinodermata, which also includes starfish, sea cucumbers, sand dollars, brittle stars, and crinoids. Like other echinoderms, they have five-fold symmetry and move by means of hundreds of tiny, transparent, adhesive tube feet. The term 'sea urchin' refers to the 'regular echinoids', which are symmetrical and globular, and includes two subclasses: Euechinoidea and Cidaroidea. Irregular sea urchins, such as sand dollars and heart urchins, have evolved flattened or oval shapes for burrowing. Together with sea cucumbers, they make up the subphylum Echinozoa, characterized by a globoid shape without arms.
Reader's Guide
Sea urchins have been studied since the 19th century as model organisms in developmental biology because their embryos are easy to observe. This has continued with studies of their genomes due to their unusual fivefold symmetry and relationship to chordates. The closest echinoderm relatives of sea urchins are sea cucumbers, which like them are deuterostomes, a clade that includes chordates. Sea urchins are also popular in aquaria, where species such as the slate pencil urchin are useful for controlling algae. Fossil urchins have been used as protective amulets. When unchecked by predators, urchins can create urchin barrens, damaged environments devoid of large algae and the animals associated with them. The structure of the mouth and teeth has been found to be so efficient at grasping and grinding that similar structures have been tested for use in mechanical applications.
Did You Know?
- Sea urchins have a rigid test composed of fused plates of calcium carbonate covered by a thin dermis and epidermis.
- The name 'urchin' is an old word for hedgehog, which sea urchins resemble.
- Sea urchins convert aqueous carbon dioxide using a catalytic process involving nickel into the calcium carbonate portion of the test.
- The jaw apparatus of sea urchins is known as Aristotle's lantern.
Frequently Asked Questions
What are Sea urchin's key traits and abilities?
Sea urchins display a distinctive fivefold radial symmetry and crawl along the seafloor using tiny tube feet and their spines. They feed primarily on algae but will also take in slow or stationary animals, and their dense spiny armor serves as the main defense against most predators.
Who preys on Sea urchin?
A range of animals hunt sea urchins, including sharks, sea otters, starfish, wolf eels, and triggerfish, while humans also harvest them for food. Their spiny test is the primary barrier keeping these predators at bay.
Why is Sea urchin important to science and culture?
Since the 19th century, sea urchins have been valued as model organisms in developmental biology because their large, easily observed eggs make them ideal for studying cell division and early embryogenesis. Fossil urchin tests have also been repurposed throughout history as decorative amulets.
Where does Sea urchin live?
Sea urchins inhabit every ocean, from the intertidal zone right down to hadal depths in the abyssal sea. They are slow-moving benthic animals that settle on the seabed rather than swimming freely in the water column.
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