Extant Orders of the Asteroidea
A survey of asteroid nomenclature arranged by order has been compiled. Clark (1989, 1993, 1996) and Clark and Mah (2001) list accepted names as well as synonyms, otherwise invalid names, references and ranges of type localities.
Brisingida—Brisingids are deep-sea dwelling asteroids. They usually have many (6-16) long, attenuated arms which are used in suspension feeding. The Brisingida contains about 100 species in 17 genera and 6 families. A preliminary phylogeny for this order has been produced by Mah (1998).
Forcipulatida—These asteroids are distinguished by their forcipulate pedicellariae, which are generally quite conspicuous on the body surface. The Forcipulatida contains about 300 species in 68 genera and 6 families. A preliminary phylogeny for this order has been produced by Mah (2000).
Notomyotida—These are deep-sea dwelling asteroids having flexible arms with characteristic longitudinal muscle bands along the inner dorsolateral surface. The Notomyotida contains about 75 species in 12 genera and 1 family.
Paxillosida—These asteroids are considered to be somewhat infaunal in that they can bury themselves partially under sandy sediments. They are characterized by some morphological features (e.g. pointed, unsuckered tubefeet) which have been considered primitive by some (see Discussion of Phylogenetic Relationships, below). The Paxillosida contains about 255 species in 46 genera and 5 families.
Spinulosida—These asteroids have a relatively delicate skeletal arrangement and completely lack pedicellariae. No fossil spinulosids have been found. The Spinulosida contains about 120 species in 9 genera and 1 family.
Valvatida—These asteroids are quite diverse, but are often characterized by their conspicuous marginal ossicles. Definition of this group has been the most variable and the ordinal definition of many families included here has been controversial (see Discussion of Phylogenetic Relationships, below). The Valvatida contains about 695 species in 165 genera and 14 families.
Velatida—These asteroids typically have thick bodies with large discs and interradial depressions. Contrary to Blake's (1987) classification, molecular evidence suggests a relationship between some velatid and valvatid families (see Discussion of Phylogenetic Relationships, below). The Velatida contains about 200 species in 25 genera and 5 families.