Crinoidea
Crinoidea
Crinoidea (/kraɪˈnɔɪdiə/; from the Greek words "krinon", "a lily", and "eidos", "form") is a class of echinoderms that includes more than 600 species of sea lilies and feather stars living today.
Etymology
The term Crinoidea comes from the Greek words "krinon", meaning "a lily", and "eidos", meaning "form". This is due to the resemblance of many crinoids to the flower of a lily.
Anatomy
Crinoidea are characterized by 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.
Classification
Crinoidea is a class within the phylum Echinodermata, which also includes the starfish (Asteroidea), sea urchins (Echinoidea), brittle stars (Ophiuroidea), and sea cucumbers (Holothuroidea).
Fossil Record
Crinoids are an ancient fossil group that first appeared in the seas of the Middle Cambrian, about 300 million years before dinosaurs. They flourished during the Paleozoic and Mesozoic, and some survive to the present day.
Related Terms
- Echinodermata: The phylum that includes crinoids, as well as starfish, sea urchins, brittle stars, and sea cucumbers.
- Asteroidea: The class of echinoderms that includes starfish.
- Echinoidea: The class of echinoderms that includes sea urchins.
- Ophiuroidea: The class of echinoderms that includes brittle stars.
- Holothuroidea: The class of echinoderms that includes sea cucumbers.
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