what are pedicellarial state their function
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Echinoderm, any of a variety of invertebrate marine animals belonging to the phylum Echinodermata, characterized by a hard, spiny covering or skin. Beginning with the dawn of the Cambrian Period (542 million to 488 million years ago), echinoderms have a rich fossil history and are well represented by many bizarre groups, most of which are now extinct. Living representatives include the classes Crinoidea (sea lilies and feather stars), Echinoidea (sea urchins), Holothuroidea (sea cucumbers), Asteroidea (starfishes, or sea stars), Ophiuroidea (basket stars and serpent stars, or brittle stars), and the recently discovered Concentricycloidea (sea daisies).
Echinoderms exhibit a variety of body plans. The starfishes are also called sea stars. Although they commonly have five arms, some can have many more. Basket stars have branched and coiling arms. Many brittle stars are quick and agile in comparison to most other echinoderms, especially the almost immobile sand dollar. Sea cucumbers are elongated, soft-bodied echinoderms, while sea urchins are globular and spiny. The adult sea lily is sessile, using tentacles growing from its arms to feed.Encyclopædia Britannica, Inc.
Echinoderms have been recognized since ancient times; echinoids, for example, were used extensively by Greeks and Romans for medicinal purposes and as food. During the Middle Ages, fossil echinoids and parts of fossil crinoids were objects of superstition. In the early part of the 19th century, Echinodermata was recognized as a distinct group of animals and was occasionally associated with the cnidarians and selected other phyla in a division of the animal kingdom known as the Radiata; the concept of a superphylum called Radiata is no longer valid.
Echinoderms are separated into 21 classes, based mainly on differences in skeletal structures. The number of extant species exceeds 6,500, and approximately 13,000 fossil species have been described.
muscle: Echinoderms
The phylumEchinodermata comprises the starfishes, sea urchins, and their relatives.…
General Features
Size range and diversity of structure
Although most echinoderms are of small size, ranging up to 10 centimetres (four inches) in length or diameter, some reach relatively large sizes; e.g., some sea cucumbers are as long as two metres (about 6.6 feet), and a few starfishes have a diameter of up to one metre. Among the largest echinoderms were some extinct (fossil) crinoids (sea lilies), whose stems exceeded 20 metres in length.
Echinoderms exhibit a variety of body plans. The starfishes are also called sea stars. Although they commonly have five arms, some can have many more. Basket stars have branched and coiling arms. Many brittle stars are quick and agile in comparison to most other echinoderms, especially the almost immobile sand dollar. Sea cucumbers are elongated, soft-bodied echinoderms, while sea urchins are globular and spiny. The adult sea lily is sessile, using tentacles growing from its arms to feed.Encyclopædia Britannica, Inc.
Echinoderms have been recognized since ancient times; echinoids, for example, were used extensively by Greeks and Romans for medicinal purposes and as food. During the Middle Ages, fossil echinoids and parts of fossil crinoids were objects of superstition. In the early part of the 19th century, Echinodermata was recognized as a distinct group of animals and was occasionally associated with the cnidarians and selected other phyla in a division of the animal kingdom known as the Radiata; the concept of a superphylum called Radiata is no longer valid.
Echinoderms are separated into 21 classes, based mainly on differences in skeletal structures. The number of extant species exceeds 6,500, and approximately 13,000 fossil species have been described.
muscle: Echinoderms
The phylumEchinodermata comprises the starfishes, sea urchins, and their relatives.…
General Features
Size range and diversity of structure
Although most echinoderms are of small size, ranging up to 10 centimetres (four inches) in length or diameter, some reach relatively large sizes; e.g., some sea cucumbers are as long as two metres (about 6.6 feet), and a few starfishes have a diameter of up to one metre. Among the largest echinoderms were some extinct (fossil) crinoids (sea lilies), whose stems exceeded 20 metres in length.
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