Sea daisy

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iSea daisies

Scientific classification

Kingdom:	Animalia
Phylum:	Echinodermata
Class:	Asteroidea
Order:	Peripoda Baker, Rowe & Clark, 1986
Family:	Xyloplacidae
Genus:	Xyloplax

Species

X. medusiformis
X. turneae
X. janetae

Sea daisies (Infraclass Concentricycloidea; order Peripoda) make up an unusual group of deep-sea taxa belonging to the phylum Echinodermata, with three species described in the genus Xyloplax.

[edit] Characteristics

These species have disk-shaped flattened body and are less than 1 cm in diameter. They have a water-vascular system and are dotted with tube feet around the edge of the disk. They do not have arms, but five ambulacral areas. A gut is either reduced or absent, depending on the species. An oral opening is present, but it is unclear how these organisms derive their nutrition.

Sea daisies typically have two circumoral canals and a single peripheral ring of tube feet (i.e., podia). Concentricyloids (commonly known as sea daisies) were supported as members of the asteroid lineage, although its exact relationship to other asteroids is likely to remain a contentious issue.

[edit] Distribution

Sea daisies have been discovered in three localities, including deep-sea habitats off New Zealand, the Bahamas and most recently from the northern central Pacific. They have been collected primarily from sunken, deep-sea (1000+ meters) wood. Although known from only a handful of specimens initially, nearly 100 specimens have been collected from the Bahamas with decent numbers collected from the north central Pacific.

[edit] Classification

They were discovered in 1986 and their position within the echinoderms has been contentious, being placed at first in a new class, Concentricycloidea. As of 2006, they are considered the sister branch to the Infraclass Neoasteroidea, which represents all post-Paleozoic asteroids (i.e., modern Asteroidea), within the Class Asteroidea.

Class Asteroidea Infraclass Concenricycloidea Order Peripodida Family Xyloplacidae