Christmas Anemone

Urticina crassicornis is biradially symmetrical and ranges from 2 - 12.7 cm tall with a width of 1 - 7.6 cm. This sea anemone has a solid basal plate which is always flat. Its column can be olive green with or without red spots, solid red, cream, or brown. It always has small, inconspicuous tubercles but no acontia. Its tubercles are not white and do not usually accumulate bits of sand, gravel and shell. The tentacles, superior of the column and usually 100 in number, are green to opaque cream with red and white striations and semi-transparent when extended. The tentacles are conical, thick and blunt and arranged in 3 - 5 circular rings around the oral disc. The oral disc has no white striations and usually has the same color scheme as the tentacles.

Urticina crassicornis is found in the north Pacific Ocean (along coasts of both Asia and North America), north Atlantic Ocean (North America and Europe) and Arctic Ocean (Asia, Europe and North America). In the northeastern Pacific Ocean, it ranges from intertidal and subtidal zones of the Pribilof Islands, Alaska to Monterey, California. In the Atlantic Ocean, it is found in intertidal and subtidal zones ranging from the Arctic Ocean above Newfoundland, Canada to Cape Cod, Massachusetts (USA), and also along the coasts of northwestern Europe. In the state of Washington this sea anemone more commonly frequents the Puget Sound compared to the Pacific Ocean front. It is found in a lower intertidal, upper subtidal zone - 30 m deep, inhabiting well protected and shaded areas. Urticina crassicornis is a benthic and sessile organism, firmly attached only to hard substrata.

A non-selective and opportunistic predator, Urticina crassicornis, may feed on crabs, sea urchins, mussels, gastropods, chitons, barnacles, fish, and sometimes sea stars and stranded jellies. A peculiar prey, the sun star, Pycnopodia helianthoides commonly known as the "Sunflower Star", is found in Washington state and has a size much greater than U. crassicornis, sometimes ranging up to 3 ft. in armspan. This anemone exhibits both intracellular and extracellular digestion. Food is caught within the tentacles which then move the prey towards the oral disc.

Urticina crassicornis produces by both asexual and sexual reproduction. In the Atlantic populations, eggs and sperm are held and fertilized within the body column. The young are brooded between the mesenteries of the body and are emitted as smallish, well developed, young anemones. Spawning occurs in the spring amongst Puget Sound populations, when eggs (yolky, 0.7 mm in diameter) and sperm are released into the sea for fertilization. Urticina crassicornis's major sperm chromosomal proteins have been found to be two specialized histone H1 proteins which indicate a strong relation to the chromosomal proteins of bird and amphibians. After fertilization, a solid and ciliated blastula is created due to superficial cleavage. Six days following fertilization, a cone-shaped and benthic, larval planula develops.