Diadumene franciscana is commonly known as the San Francisco anemone.
It has only been reported from the California coast and Hawaii, but is believed to have been introduced to both regions.
Its area of origin is unknown.
Diadumene franciscana was first collected in San Francisco Bay in the 1940s and has since been found from San Diego to Tomales Bay.
It is known from estuaries and sheltered waters where it grows on pilings, floats, and seagrasses.
Like other anemones, it feeds by capturing zooplankton and small epibenthic animals with its tentacles.
When extended, the column of the polyp of Diadumene franciscana is about 2x as wide.
Most specimens are less than 20 mm high and 10 mm in diameter.
This anemone has acontia, filamentous structures lined with cnidocytes (cells bearing nematocysts), arising from the median lobes of the incomplete mesenteries, which partially subdivide the gastrovascular cavity.
The acontia may protrude into the body cavity or be expelled through pores to defend themselves when disturbed or handled.
The anemone has fewer than 100 tentacles, and there is a substantial tentacle-free zone around the mouth.
The two tentacles (called guide tentacles) at each end of the slit-shaped mouth are closer to the mouth than the other tentacles and are yellowish in color.
The body column of Diadumene franciscana is pale green, cream or gray and translucent when extended.
It often has up to 48 double or single white stripes on the column, but is sometimes stripeless.
This anemone is transparent when expanded, but cream, gray, or light green when contracted.
It is usually marked with single or double longitudinal white stripes, but may be unmarked.
Diadumene franciscana often occurs in groups as it frequently reproduces asexually (clonal formation).
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