Crinoidea

Crinoidea is a class of marine animals that are part of the phylum Echinodermata. They are characterized by their unique body structure, which includes a mouth on the top surface that is surrounded by feeding arms. Crinoids are commonly known as sea lilies or feather stars.

Anatomy

Crinoids have a mouth on the top surface that is surrounded by feeding arms. They have a U-shaped gut, and their anus is located next to the mouth. Although the basic echinoderm pattern of fivefold symmetry can be recognized, most crinoids have many more than five arms. Crinoids usually have a stem used to attach themselves to a substrate, but many live attached only as juveniles and become free-swimming as adults.

Habitat and Distribution

Crinoids are found in a variety of marine habitats, from shallow coastal waters to deep-sea trenches. There are both stalked forms, also known as sea lilies, and unstalked forms, known as feather stars or comatulids.

Fossil Record

Crinoids have a rich fossil record and have been important contributors to the biodiversity of marine ecosystems for hundreds of millions of years. The earliest known crinoids come from the Ordovician period, and they reached their peak diversity in the Mississippian subperiod of the Carboniferous period.

Classification

Crinoidea is divided into three orders: Comatulida, Isocrinida, and Hyocrinida. Comatulida, or feather stars, are the most diverse order, with over 540 species. Isocrinida, or sea lilies, are less diverse, with about 50 species. Hyocrinida is the least diverse order, with only a few species.

See Also

• Echinodermata
• Comatulida
• Isocrinida
• Hyocrinida

References

Crinoidea Resources
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