Asterias amurensis, also known as the Northern Pacific seastar and Japanese common starfish, is a seastar found in shallow seas and estuaries, native to the coasts of northern China, Korea, far eastern Russia, Japan, Alaska, the Aleutian Islands and British Columbia in Canada. Two forms are recognised: the nominate and forma robusta from the Strait of Tartary. It mostly preys on large bivalve molluscs, and it is mostly preyed on by other species of starfish. Population booms in Japan can affect the harvest of mariculture operations and are costly to combat. This species has been introduced to oceanic areas of southern Australia, and is an invasive species there causing damage to native species, especially in Tasmania. Common names It is known in English vernacular as the northern Pacific seastar, flatbottom seastar, Japanese seastar, Japanese starfish, north Pacific seastar, purple-orange seastar and Japanese common starfish. Taxonomy This species was first described in 1871 by Christian Frederik Lütken. Parasterias albertensis was described in 1914 from British Columbia by Addison Emery Verrill from a collection made late in the previous century and kept at the Smithsonian; this taxon was synonymised by Walter Kenrick Fisher in 1930. Walter Kenrick Fisher also subsumed Asterias rollestoni as a forma of A. amurensis in 1930, and further stated that A. versicolor might well intergrade with his A. amurensis f. rollestoni to the north of its range. In 1936, and subsequently in 1940, Ryori Hayashi followed Fisher's interpretation, in 1940 even subsuming Asterias versicolor as a form of A. amurensis, although Alexander Michailovitsch Djakonov in 1950 and subsequent authors have rejected this taxonomic interpretation. Asterias pectinata was described from Kamchatka by Johann Friedrich Brandt in 1834 or 1835, and synonymised with Asterias amurensis by Fisher in 1930. In the 1950 work Sea stars (Asteroids) of the USSR Seas (translation) Djakonov named five new forms of this species from the far eastern Soviet Union (recognising six forms including the nominate), although these were later all synonymised, except for one: f. robusta. Intraspecific variation There are two forms (or subspecies) are accepted in the World Register of Marine Species by Christopher Mah as of 2008: Asterias amurensis f. amurensis Lütken, 1871 – likely described from the sea off Korea. Asterias amurensis f. robusta Djakonov, 1950 – described from far eastern Russia. Description It can grow up to 50 cm in diameter, although this is exceptional and the arms usually grow