Sea daisies

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Sea daisies
Xyloplax janetae

Xyloplax janetae

Systematics
Trunk : Echinoderms (Echinodermata)
Sub-stem : Eleutherozoa (Eleutherozoa)
Class : Starfish (asteroidea)
Order : Peripodida
Family : Xyloplacidae
Genre : Sea daisies
Scientific name of the  order
Peripodida
Baker, Rowe & Clark, 1986
Scientific name of the  family
Xyloplacidae
Baker, Rowe & Clark, 1986
Scientific name of the  genus
Xyloplax
Baker , Rowe & Clark , 1986

The sea daisy ( Xyloplax ) are a close until 1986 New Zealand discovered genus of echinoderms . After its discovery , the genus was placed in a class of its own , the Concentricycloidea, but is now counted among the starfish .

It includes only three species, of which Xyloplax turnerae occurs in the Atlantic ( Caribbean , near the island of Andros ), Xyloplax medusiformis in the Pacific off New Zealand and Xyloplax janetae in the northeastern Pacific.

The known representatives of this group are only a few millimeters tall and apparently live in the deep sea at depths of up to 2000 meters. X. medusiformis was found in drill tunnels of drill clams in sunken wood, X. turnerae settled on sunken test plates , also made of wood.

The animals have a calcareous skeleton made of overlapping plates, have marginal spines and a skeletal ring around the mouth, which is probably a remnant of the ambulacral system found in echinoderms . The feet that do not have suction pads protrude between the skeletal plates. Only X. turnerae has a sac stomach; both species probably feed on bacteria that form a film on the wood.

The animals are of separate sexes and probably reproduce by means of internal fertilization. The larval development of at least the Pacific species takes place in the ovary of the female, so the animals are born fully developed ( viviparia ).

The systematic classification of the Concentricycloidea has not yet been fully clarified, currently they are mostly regarded as a sister group of the starfish (Asteroida). Alternatively, according to the current discussion, they could also be classified in the Velatida, which belongs to the starfish .

literature

  • Alan N. Baker, Francis WE Rowe, Helen ES Clark: A new class of Echinodermata from New Zealand. In: Nature. Volume 321, June 26, 1986, pp. 862-864. (nature.com)
  • Peter Ax: The system of Metazoa II. A textbook on phylogenetic systematics. Mainz / Heidelberg 2001, ISBN 3-8274-1179-3 .
  • H. Füller, H.-E. Gruner, G. Hartwich, R. Kilias, M. Moritz: Urania Tierreich, Invertebrates 2 (Annelida to Chaetognatha) . Urania-Verlag, Leipzig 1994, ISBN 3-332-00502-2 .

Individual evidence

  1. ↑ L. Mah: A new species of Xyloplax (Echinodermata: Asteroidea: Concentricycloidea) from the northeast Pacific: comparative morphology and a reassessment of phylogeny. (PDF). In: Invertebrate Biology. (The American Microscopical Society). Volume 125, No. 2, 2006, pp. 136-153. doi: 10.1111 / J.1744-7410.2006.00048.X

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