Mushroom Sea Squirt      Distaplia occidentalis



Meet your distant cousin, Distaplia.  This mushroom-shaped, two inch-sized animal is a member of the tunicate group or sea squirts. Growing up to 5 inches, it ranges from Alaska to southern California in the low intertidal and subtidal areas and is common on floats.  


Scientists, who study animal relationships, have compared the characteristics of tadpole-like tunicate larvae (quasi-backbone protecting a spinal cord, post-anal tail and gill slits) to those of vertebrates (fish, amphibians, reptiles, birds and mammals including humans), concluding that both groups should be in the same major group or phylum called Chordata. 


The Mushroom Sea Squirt, is a colonial group of individuals called zooids.  Several zooids share an excurrent siphon but have an individual incurrent siphon which moves food particles to a basket-like filter.  The exterior covering of the colony is called a tunic (hence the name tunicate) and is made of a polysaccharide which is very similar to the cellulose of plants.  There are three kinds of sea squirts (out of 2,300 species): solitary; social, where many individuals are clumped together; and compound, like the mushroom sea squirt.


The sea squirt is a hermaphrodite.  Breeding from May to July, fertilized eggs are held within a brood pouch.  In a few days larvae develop, swim off, attach head-first to a hard substrate and metamorphose, losing the tail and fins while the rest of the body rearranges. Sexual maturity develops in a few weeks with the adult living for one to three years.