Distaplia occidentalis Bancroft, 1899

Common name(s): Mushroom ascidian

Phylum Chordata
 Subphylym Urochordata
  Class Ascidiacea
   Order Enterogona
    Suborder Aplousobranchia
     Family Clavelinidae
Distaplia occidentalis from about 20 m depth, Sares Head, WA.  The attachment stalk is at the bottom.
(Photo by: Dave Cowles, July 2006)
Description:  This compound tunicate (many individuals are embedded in a common tunic) grows in a globular (sometimes flat) mass with a short, narrow attachment stalk.  The colonies are not encrusted with sand.  The pharynx of individuals has 4 rows of stigmata.  Colored from pale orange to yellow to pink to dark purplish-red or brown.  Most colonies are less than 2 cm in diameter, though they can be larger as here (up to 10 cm).  Each of the closely packed zooids has its own incurrent siphon and pharynx, but several adjacent zooids share a slightly raised common buccal or excurrent siphon and atrial cavity.

How to Distinguish from Similar Species:  Several species of similar shape are often sand-encrusted and have 5 or more rows of stigmataDistaplia smithi, which lives on the open coast, is a cluster of leaflike lobes.  Of the other common, smooth orange local tunicates, Metandrocarpa taylori is a social ascidian in which individuals live near each other and are often connected with narrow stolons or sheets of tunic but are not enclosed within the same lump of tunic. Cnemidocarpa finmarkiensis is a solitary tunicate with a very smooth, shiny tunic.

Geographical Range:  Vancouver Island, Canada to San Diego, CA

Depth Range: Intertidal to 15 m

Habitat:  Protected floats and pilings, subtidal on rocks with good current, among surfgrass roots, open coast.

Biology/Natural History:  Spawns April to late August.  Each zooid produces 2-4 sausage-shaped eggs, which are retained in a brood pouch of the atrial cavity until the tadpole larva stage.  Larve are released mainly in the morning.  Hermaphroditic.

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Dichotomous Keys:
  Flora and Fairbanks, 1966
  Kozloff 1987, 1996
  Smith and Carlton, 1975

General References:
  Carefoot, 1977
  Gotshall, 1994
  Harbo, 1999
  Johnson and Snook, 1955
  Kozloff, 1993
  Morris et al., 1980

 Scientific Articles:
Watanabe, H. and C.C. Lambert, 1973.  Larva release in response to light by the compound ascidians Distaplia occidentalis and Metandrocarpa taylori.  Biological Bulletin 144: 556-566

Web sites:

General Notes and Observations:  Locations, abundances, unusual behaviors:

Each individual has its own separate incurrent (oral) siphon but the excurrent (buccal) siphon is shared by several adjacent individuals.  This closeup shows the arrangement of individuals.

Authors and Editors of Page:
Dave Cowles (2006):  Created original page