Velatida
{{Short description|Order of starfishes}}
{{Automatic taxobox
| image = Starfish at Tafelberg deep DSC09595.JPG
| image_caption = Pteraster capensis
| taxon = Velatida
| authority = Perrier, 1884
| subdivision_ranks = Families
| subdivision = 5, see text
}}
The Velatida are an order of sea stars containing about 200 species in five families. These sea stars normally have thick bodies with large discs.{{cite web|url=http://palaeo.gly.bris.ac.uk/Palaeofiles/Fossilgroups/asteroz2/index_f/mod_fm.html |title=Asterozoa: Fossil groups: SciComms 05-06: Earth Sciences |publisher=Palaeo.gly.bris.ac.uk |date=2005-11-22 |access-date=2010-07-30}}
Description and characteristics
This order contains mostly deep or cold seas sea stars, often with a wide distribution (sometimes global). They have a pentagonal or star shape, with between 5 and 15 arms. Their skeleton is weakly developed, which confers them a good flexibility, and numerous papillae on the aboral surface allow them to breathe in poorly oxygenated waters. Their pedicellariae are often provided with spines. The smallest are Caymanostellidae (between 0,5 and 3 cm) and the biggest Pterasteridae (up to 30 cm).{{cite web |url=http://www.accessscience.com/content/velatida/900662 |title=Velatida |last1=Mah |first1=Christopher L. |website=www.accessscience.com }}
Taxonomy
New molecular evidence now suggests a relationship between some velatid and valvatid families.
List of families according to World Register of Marine Species:{{cite web|url=http://www.marinespecies.org/asteroidea/aphia.php?p=taxdetails&id=123091 |title=The World Asteroidea Database - Velatida |publisher=Marinespecies.org |access-date=2010-07-30}}
- Caymanostellidae Belyaev, 1974
- Korethrasteridae Danielssen & Koren, 1884
- Myxasteridae Perrier, 1885
- Pterasteridae Perrier, 1875
- †Tropidasteridae Wright, 1880
Image:Peribolaster.jpg|Peribolaster sp., Korethrasteridae
Image:Myxaster.jpg|Myxaster sp., Myxasteridae
Image:Translucent sea star.jpg|Hymenaster sp., Pterasteridae