Sea daisy
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| Sea daisies | ||||||||||||
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X. medusiformis |
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.
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[edit] Characteristics
Sea daisies (or concentricycloids) have a disk-shaped flattened body and are generally less than 3 cm in diameter. They have a water vascular system, typically with two concentric circumoral canals and a single peripheral ring of 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.
[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
Since they were discovered in 1986, their position within the echinoderms has been debated. At first they were placed in a new class, Concentricycloidea, since it was unclear whether they might have affinities with asteroids or ophiuroids. The former view gained acceptance, and since 2006, they are currently considered a sister group to the Infraclass Neoasteroidea, which represents all post-Paleozoic asteroids within the Class Asteroidea.
Class Asteroidea, Infraclass Concentricycloidea, Order Peripoda (or Peripodida), Family Xyloplacidae
- Genus Xyloplax
- Xyloplax medusiformis
- Xyloplax turneae
- Xyloplax janetae
