Scientific Name and Authority

Botryllus planus   (Van Name, 1902) 


Botryllus planus is a colonial tunicate with encrusting colonies. Colonies are often irregular in shape and several centimeters in greatest diameter. They are frequently so thin that the zooids are sometimes nearly parallel to the colonies surface, but in other cases, colonies are thicker and the zooids nearly upright. The color is very variable during life. Zooids range from orange, dark purple, purplish brown, or blackish with a white, pale green, or golden yellow area surrounding the branchial orifice of each zooid. The colonies' light colors fade after death to purple or brownish purple. 'Some specimens collected at Bermuda were bright orange when alive, this color suffusing the tunic as well as the zooids. The young zooids produced by budding are in many colonies differently colored than the adult ones from which they developed (Van Name 1945).

Zooids are smaller than 1.5 to 1.75 mm in length when preserved. Zooids have eight or fewer tentacles, and usually 11 to 13 rows of stigmata. 'The reproductive and digestive organs furnish the easiest means of distinguishing this species. The male organs consist of a single testis on each side of the body, situated posterior to the middle and so deeply cleft into numerous (10 to 20) rounded lobes that it appears like a rosette shaped mass of small separate glands. The female organs, at least in the adult state, consist of a single ovary on each side, each containing a large egg situated close, and directly anterior, to the testis. The stomach is oblong or barrel shaped though tapering somewhat more toward the pyloric end. The stomach has about nine complete glandular folds and one incomplete one, which increase gradually in prominence toward the esophageal end, and a very long tubular curved pyloric caecum that is slightly enlarged at the extreme end.' (Van Name 1945).

Taxonomic Classification:

Kingdom: Animalia
Phylum: Chordata
Subphylum: Tunicata
Class: Ascidiacea
Order: Stolidobranchia
Family: Styelidae
Genus: Botryllus
Species: planus


Botrylloides nigrum planum (Van Name, 1902)

Potentially Misidentified Species:

Botryllus nigrum