Sea-star diversity on the Pacific coast of North America is the highest of anywhere in the world.  On a single SCUBA dive one can expect to see a dozen or more species.  Diversity of intertidal forms is less, but number of individuals, for example, ochre stars Pisaster ochraceus, may be great. 

NOTE “sea star” or “starfish”?  According to the Oxford English Dictionary, the first literature reference to asteroids was in 1538 to a type of  “sterrefyshe”, and the designation “sea star” did not appear until 1672.  Contemporary invertebrate textbooks refer to asteroids as “sea stars”, and this is the term used in the ODDYSEY.  The first part of the name reminds us that echinoderms live only in the sea.  As for the pentaradiate symmetry implied by the second part, consider this. Of 37 species of asteroids in British Columbia, 30 have 5 arms (a classic "star"), and 7 have more than 5, so the “star” designation is mostly applicable.  The sunflower star Pycnopodia helianthoides has up to 40 arms and, at sizes up to 1.3m across, is the largest diameter asteroid in the world.  Larger in mass than Pycnopodia is the pink sea star Pisaster brevispinus, and this species is the largest 5-armed sea star in the world (60cm dia). 

Ochre stars Pisaster ochraceus sheltering
in a crevice on the west coast of Vancouver
Island, British Columiba during low tide 0.3X

Phylum Echinodermata (lit. “spiny skin” G.) including sea lilies, sea stars, sea urchins, sea cucumbers, and brittle stars

Class Asteroidea (lit. “like a star” G.), including sea stars

NOTE  some recent name changes in west-coast asteroids include: bat stars changed from Patiria miniata to Asterina miniata and then back again.  Blood stars Henricia spp. remain a “puzzling complex”; however, whatever species name used by an author will be the one used in the ODYSSEY.  Mah 2007 p. 927 and 922, respectively, In The Light and Smith Manual Intertidal invertebrates from central California to Oregon (Carlton, ed.) U Cal Press, Berkely.