Cnidaria
Sea anemones & relatives
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There are 20 or more large and conspicuous sea anemones (Subphylum Anthozoa) that can be seen intertidally or encountered subtidally by SCUBA divers in the northwest coast of North America.

NOTE  named after a common large flower (ranunculacean) 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

   

ANIMATION of the snail's odyssey © Thomas Carefoot 2023
map used by the snail in A SNAIL'S ODYSSEY

To navigate through the ODYSSEY:

  • Select a TOPIC from the menu at the top of the screen
  • OR: play the animation to the left
  • OR: follow the snail's ODYSSEY by CLICKING on any X-marked invertebrate on the map above

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 (or subphylum) 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, Metridium¹, Cribrinopsis², 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

NOTE¹ references to Metridium senile in the scientific literature on west-coast sea anemones most likely included two related types, now separated into a larger (up to 1m in height), subtidal species known as Metridium farcimen (= M. giganteum) and two smaller, intertidal/subtidal species designated M. exilis and M. 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.

NOTE² in a recent paper a consortium of Russian and Canadian scientists splits the commonly designated snakelock anemone Cribrinopsis fernaldi into two species based upon morphological and molecular data. The first, the one we usually consider as C. fernaldi, is larger with longer tentacles, has a conspicuous ring of marginal projections (verrucae) around the top of the column, has a white column with pinkish tentacles, and usually inhabits muddy bottoms. The other, now designated as C. rubens n. sp. is smaller with shorter tentacles, unformly red or white in colour, and inhabits rocky habitats. The two species also differ in their complements of cnidae (nematocysts). Sanamyan et al. 2019 Mar Biodiv https://doi.org/10.1007/s12526-019-00956-w

Fig. 1.  Snakelock anemone Cribrinopsis fernaldi with inset photo showing close view of verrucae on the upper column rim 
Fig. 2.  Sea anemone Cribrinopsis rubens n. sp. on rock wall showing red and white colour morphs 0
Courtesy Neil McDaniel, British Columbia
   
There used to be just one species of plumose anemone on the west coast of North America, Metridium sessile, which is a smaller type commonly found intertidally, but this is now separated from a much larger type, M. farcimen, found only subtidally.  The former reproduces both sexually and asexually (longitudinal fission), but the latter only reproduces sexually.  The large specimens in the video are likely to be M. farcimen; smaller clones of M. senile are also visible