There are 20 or more large and conspicuous sea anemones that can be seen intertidally or encountered subtidally by SCUBA divers in the northwest coast of North America. 

NOTE  lit. “wind flower” G., referring to a a common large flower (ranunculaceans) widespread in temperate areas.  Early references (e.g., in the 1550s) to anemones in English literature are to the flower while the designation “sea” anemone does not appear until the 1770s

Phylum Cnidaria (lit. “nettle-bearing” G.), referring to the nematocysts possessed by all members of the phylum; includes sea anemones, corals, sea pens, gorgonians, jellyfishes, hydroids

Class Anthozoa  (lit. “flower animal” G.), including sea anemones, sea pens, soft corals, and cup corals

Subclass Hexacorallia (=Zoantharia) (lit. “six coral” G.), referring to six sets of mesenteries

Order Actiniaria (lit. “beach/seashore” G.), including sea anemones such as Anthopleura, Urticina, Epiactus, Metridium, and others

Order Ceriantharia, including tube-inhabiting, burrowing anemones such as Pachyceriathus imbricata

Order Corallimorpharia (lit. “coral form” G.), including Corynactis californica

Order Scleractinia (lit. “hard” G.), including cup corals Balanophyllia spp.

Order Zoanthidea (=Zoanthiniaria), including epizoanthids Epizoanthus scotinus

NOTE   early references to Metridium senile in the scientific literature on west-coast sea anemones likely included 2 species, now separated into a larger (up to 1m in height), subtidal species known as Metridium farcimen (= M. giganteum) and 2 smaller, intertidal/subtidal species designated M. exilis and senile.  When it is clear that the larger species is being referred to in a research paper, the name M. farcimen is substituted. For a morphological, biochemical, and genetical analyses of the Metridium spp. complex see Bucklin & Hedgecock 1982 Mar Biol 66: 1.

In a later study on the same research topic of the Metridium complex, another set of authors asks, “how did an organism as conspicuous as M. giganteum escape formal description until now?”. The question is not really a fair one, as the authors of the 1982 paper do describe its presence, but just fail to provide a name for it. Fautin et al. 1989 The Wasmann J Biol 47: 77.