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Giant Green Anemone

Anthopleura xanthogrammica


The giant green anemone has a column diameter of up to 7 inches and a tentacular crown diameter of up to 10 inches, and may grow to a height of 12 inches.

The short, conical tentacles are arranged in six or more rings surrounding the mouth.

The column is dark green to brown in color, with irregular tubercles on the surface. The disk and tentacles are green or blue to white, depending on how much sunlight the anenome receives. This is because the anemone has symbiotic algae living inside its tissues. Under strong sunlight the algae is encouraged to grow and the sea anemone gets very green. In shade the algae's growth is inhibited, causing the anemone to lose color, sometimes to the point of being almost white.

Giant Green Anemone

Distribution and Habitat

This anemone is primarily found along the west coast of North and Central America, from Alaska south to Panama. However, it has also been found in Hudson Bay, Canada, as well as on the eastern coast of Russia. It is typically seen attached to substrate (including manmade structures such as concrete pilings) in locations with cold waters and high wave activity, at depths up to 49 feet. It is particularly fond of mussel beds.

Life Cycle

Spawning in this species seems to be triggered by warmer water temperatures.

Females release thousands of eggs at a time, and have been observed to do so multiple times within a short period. Males release sperm, which disperses rapidly.

Cell cleavage begins within 3 hours after fertilization and development continues to a planula stage, during which the larvae swim or float freely, allowing them to disperse over great distances. Larvae feed on zooplankton, phytoplankton, and even other larvae, all of which are "caught" by means of a secreted mucus thread. Once larvae find suitable locations, they attach to substrate and develop their pedal disks, completing metamorphosis into adults. Settlement occurs at least 3 weeks after fertilization.

Sexual maturity takes 5 to 10 years.


Giant green anemones feed primarily on sea urchins, detached mussels, crabs, and small fish.

Once prey is in reach, an anemone stretches its tentacles and paralyzes its prey using the nematocysts on its tentacles. It then uses its tentacles to bring food directly to the mouth.

Other Information

Although it is usually a solitary animals, groups of up to 14 individuals per square meter are also common. They are not typically aggressive toward each other, but individuals that have been transplanted from one colony to another may induce aggressive behavior.

Sea anemones tend to spend their entire post-larval lives in one spot, but it is not uncommon for an individual to change locations in order to take advantage of better conditions.

Scientific Classification

phylum Cnidaria
class Anthozoa
order Actiniaria
family Actiniidae
genus & species Anthopleura xanthogrammica

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This page was last updated on 03/24/2018.