Sea urchins (/ˈɜːrtʃɪnz/) are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin are distributed on the seabeds of every ocean and inhabit every depth zone from the intertidal seashore down to 5,000 meters (16,000 ft; 2,700 fathoms).[1] The spherical, hard shells (tests) of sea urchins are round and covered in spines. Most urchin spines range in length from 3 to 10 cm (1 to 4 in), with outliers such as the black sea urchin possessing spines as long as 30 cm (12 in). Sea urchins move slowly, crawling with tube feet, and also propel themselves with their spines. Although algae are the primary diet, sea urchins also eat slow-moving (sessile) animals. Predators that eat sea urchins include a wide variety of fish, starfish, crabs, marine mammals, and humans.
Like all echinoderms, adult sea urchins have fivefold symmetry, but their pluteus larvae feature bilateral (mirror) symmetry, indicating that the sea urchin belongs to the Bilateria, along with chordates, arthropods, annelids and molluscs. Sea urchins are found in every ocean and in every climate, from the tropics to the polar regions, and inhabit marine benthic (sea bed) habitats, from rocky shores to hadal zone depths. The fossil record of the Echinoids dates from the Ordovician period, some 450 million years ago. The closest echinoderm relatives of the sea urchin are the sea cucumbers (Holothuroidea), which like them are deuterostomes, a clade that includes the chordates. (Sand dollars are a separate order in the sea urchin class Echinoidea.)
The animals have been studied since the 19th century as model organisms in developmental biology, as their embryos were easy to observe. That has continued with studies of their genomes because of their unusual fivefold symmetry and relationship to chordates. Species such as the slate pencil urchin are popular in aquaria, where they are useful for controlling algae. Fossil urchins have been used as protective amulets.
^"Animal Diversity Web – Echinoidea". University of Michigan Museum of Zoology. Retrieved 26 August 2012.
Seaurchins (/ˈɜːrtʃɪnz/) are spiny, globular echinoderms in the class Echinoidea. About 950 species of seaurchin are distributed on the seabeds of every...
The red seaurchin (Mesocentrotus franciscanus) is a seaurchin found in the northeastern Pacific Ocean from Alaska to Baja California. It lives in shallow...
Purple seaurchin can refer to one of several species of seaurchin: Arbacia punctulata, a species of seaurchin from the family Arbaciidae commonly known...
Seaurchin injuries are caused by contact with seaurchins, and are characterized by puncture wounds inflicted by the animal's brittle, fragile spines...
use tools. In most of its range, it is a keystone species, controlling seaurchin populations which would otherwise inflict extensive damage to kelp forest...
White seaurchin is a common name for several seaurchins and may refer to: Lytechinus anamesus [Wikidata] Salmacis sphaeroides [Wikidata] Tripneustes...
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Several species of seaurchin share the name green seaurchin: Lytechinus variegatus, also known as the variegated seaurchin Psammechinus microtuberculatus...
of cacti native to South America, sometimes known as hedgehog cactus, sea-urchin cactus or Easter lily cactus. As of October 2023[update], there are about...
gastrulation, the blastocoel has been obliterated. At the 120- cell stage, the seaurchin embryo is considered a blastula because of its developed blastocoel, which...
which includes starfish, brittle stars, seaurchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally...
echinoderms (phylum Echinodermata), particularly in sea stars (class Asteroidea) and seaurchins (class Echinoidea). Each pedicellaria is an effector...
Echinodermata, which also includes the starfish, brittle stars, seaurchins and sea cucumbers. They live in both shallow water and in depths as great...
gastrulation in the seaurchin. Recent simulations found that planar cell polarity is sufficient to drive seaurchin gastrulation. Seaurchins exhibit highly...
also eat dead algae that they find. Some seaurchins, such as the variegated seaurchin or the red seaurchin, have become popular as pets for home aquariums...
masses, of fish and certain marine animals such as shrimp, scallop, seaurchins and squid. As a seafood, roe is used both as a cooked ingredient in many...
Arbacia lixula, the black seaurchin, is a species of seaurchin from Europe. It is a medium-sized seaurchin, characterized by its deep black color and...
Strongylocentrotus purpuratus is a species of seaurchin in the family Strongylocentrotidae commonly known as the purple seaurchin. It lives along the eastern edge...
invasive species. Sea Stars (starfish) are the main predators of kelp-eating seaurchins. Satellite imagery shows that seaurchin populations have exploded...
as the lime urchin, black seaurchin, or the long-spined seaurchin, is a species of seaurchin in the family Diadematidae. This seaurchin is characterized...
prey to fill their diets. They are predatory, feeding mostly on seaurchins, clams, sea snails, and other small invertebrates. Although the species was...
made of calcium carbonate cemented onto other surfaces. The shells of seaurchins are called "tests", and the moulted shells of crabs and lobsters are...
Ecological role of purple seaurchins. Science 314: 940-941. Filbee-Dexter, Karen; Scheibling, Robert E. (2014-01-09). "Seaurchin barrens as alternative...
development of the seaurchin, a marine invertebrate. The larval seaurchin does not resemble its adult form, because the seaurchin is an indirect developer...
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