26 Facts About Sea urchins

Sea urchins are spiny, globular echinoderms in the class Echinoidea.

Sea urchins move slowly, crawling with tube feet, and propel themselves with their spines.

Predators that eat sea urchins include a wide variety of fish, starfish, crabs, marine mammals.

Adult sea urchins have fivefold symmetry, but their pluteus larvae feature bilateral symmetry, indicating that the sea urchin belongs to the Bilateria group of animal phyla, which comprises the chordates and the arthropods, the annelids and the molluscs, and are found in every ocean and in every climate, from the tropics to the polar regions, and inhabit marine benthic habitats, from rocky shores to hadal zone depths.

Sea urchins are members of the phylum Echinodermata, which includes sea stars, sea cucumbers, brittle stars, and crinoids.

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The "irregular" sea urchins are an infra-class inside the Euechinoidea, called Irregularia, and include Atelostomata and Neognathostomata.

Several sea urchins including the sand dollars, are oval in shape, with distinct front and rear ends, giving them a degree of bilateral symmetry.

Sea urchins might appear to be incapable of moving but this is a false impression.

Sea urchins have no visible eyes, legs, or means of propulsion, but can move freely but slowly over hard surfaces using adhesive tube feet, working in conjunction with the spines.

Sea urchins convert aqueous carbon dioxide using a catalytic process involving nickel into the calcium carbonate portion of the test.

Sea urchins move by walking, using their many flexible tube feet in a way similar to that of starfish; regular sea urchins do not have any favourite walking direction.

Mouth of most sea urchins is made up of five calcium carbonate teeth or plates, with a fleshy, tongue-like structure within.

Sea urchins possess a hemal system with a complex network of vessels in the mesenteries around the gut, but little is known of the functioning of this system.

In general, sea urchins are negatively attracted to light, and seek to hide themselves in crevices or under objects.

Regular sea urchins have five gonads, lying underneath the interambulacral regions of the test, while the irregular forms mostly have four, with the hindmost gonad being absent; heart urchins have three or two.

Mass mortality of sea urchins was first reported in the 1970s, but diseases in sea urchins had been little studied before the advent of aquaculture.

Adult sea urchins are usually well protected against most predators by their strong and sharp spines, which can be venomous in some species.

Sea urchins are one of the favourite foods of many lobsters, crabs, triggerfish, California sheephead, sea otter and wolf eels.

Sea urchins otters have re-entered British Columbia, dramatically improving coastal ecosystem health.

Sea urchins are established in most seabed habitats from the intertidal downwards, at an extremely wide range of depths.

Sea urchins can be found in all climates, from warm seas to polar oceans.

Sea urchins are being used in longevity studies for comparison between the young and old of the species, particularly for their ability to regenerate tissue as needed.

Scientists at the University of St Andrews have discovered a genetic sequence, the '2A' region, in sea urchins previously thought to have belonged only to viruses that afflict humans like foot-and-mouth disease virus.

Beyond embryology, urchins provide an opportunity to research cis-regulatory elements.

Importantly, Sea urchins act as the closest living relative to chordates and thus are of interest for the light they can shed on the evolution of vertebrates.

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However, sea urchins are commonly eaten by the Alaska Native population around Kodiak Island.