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).^[2]

New molecular evidence now suggests a relationship between some velatid and valvatid families.

List of families according to World Register of Marine Species:^[3]

• Caymanostellidae Belyaev, 1974
• Korethrasteridae Danielssen & Koren, 1884
• Myxasteridae Perrier, 1885
• Pterasteridae Perrier, 1875
• †Tropidasteridae Wright, 1880

•  
  Peribolaster sp., Korethrasteridae
•  
  Myxaster sp., Myxasteridae
•  
  Hymenaster sp., Pterasteridae