Sea Urchin

A Sea Urchin is a spiny, globular echinoderm.

• Context:
  • It can exhibit radial symmetry and endoskeletal structures common among Echinoderms.
  • It can display a variety of morphologies from nearly spherical to slightly flattened.
  • It can (range) from being a Shallow Water Urchins to being a Hadal Zone Urchin (Hadal zone).
  • It can serve as a Developmental Biology Model Organism, providing insights into early bilateral developmental stages.
  • It can be a crucial component of marine ecosystems, influencing benthic community structure through their feeding habits.
  • ...
• Example(s):
  • a Mississippian Period Urchin (Mississippian period), such as Archaeocidaris.
  • an Eucidaris tribuloides, known as the slate pencil urchin, demonstrating adaptations to different environmental conditions.
  • an Ordovician Period Urchin (Ordovician).
  • a Pacific Ocean Urchin, such as:
    • a Pacific Red Urchin.
    • a Pacific Purple Urchin.
    • a Collector Urchin (Tripneustes gratilla).
    • a Long-Spined Sea Urchin (Diadema setosum).
    • a Flower Urchin (Toxopneustes pileolus), famous for their potent venom.
    • a Slate Pencil Urchin (Heterocentrotus mammillatus).
  • ...
• Counter-Example(s):
  • Sand Dollars, which, while closely related to sea urchins and sharing the same class (Echinoidea), have distinct skeletal structures and life habits.
  • ...
• See: Tripneustes Ventricosus, Echinometra Viridis, Perischoechinoidea, Cidaroida, Euechinoidea, Atelostomata, Cassiduloida, Spatangoida, Uni.

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References

2024

• (Wikipedia, 2024) ⇒ https://en.wikipedia.org/wiki/sea_urchin Retrieved:2024-4-24.
  • Sea urchins () 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 . The spherical, hard shells (tests) of sea urchins are round and covered in spines. Most urchin spines range in length from , with outliers such as the black sea urchin possessing spines as long as . 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.

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