Biodiversity & Conservation

A colonial sea squirt - Botrylloides violaceus

Botrylloides violaceus

Image Judith Oakley - Botrylloides violaceus from marina pontoon. Image width ca 20 cm.
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Distribution map

Botrylloides violaceus recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

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Botrylloides violaceus is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Chordata Sea squirts, fish, reptiles, birds and mammals
Class Ascidiacea Sea squirts
Authority Oka, 1927
Recent synonyms None
Map icon Recorded Distribution in Britain and Ireland Recorded from the southern coast of the UK at the following locations in 2004: Gosport, Southampton, Hamble, Poole, Exmouth & Queen Anne's Battery in Plymouth. Also recorded from Milford Haven.
Habitat information icon Habitat information Found on artificial surfaces in shallow water, especially in harbours and marinas. Also found attached to macroalgae and other unitary sea squirts, for example Styela clava.
Text page icon Description Botrylloides violaceus is a colonial sea squirt forming lobed sheets usually 2-3 mm in thickness. Individual colonies are always one colour. The colonies can be different colours, e.g. dark brown, brick red, orange, purple and yellow. The zooids are arranged in a variety of ways, roughly oval groups or meandering, occasionally branching, double rows or chains.
Identifying features
  • Thick sheets or lobes adhering to the surface; may grow back-to-back.
  • Uniform in colour, can be dark brown, brick red, orange, purple and yellow.
  • Zooids arranged in roughly oval groups or meandering, occasionally branching, double-rows or chains.
  • The form and structure of the larva is a conclusive feature to aid with identification.
Additional information icon Additional information A non-native species from Japan recorded in the UK for the first time in 2004. The one-toned colouration of Botrylloides violaceus distinguishes it from Botrylloides leachi and Botryllus schlosseri. Furthermore, Botryllus schlosseri has star-like zooid arrangements.

Depending on the season (July to September) it is possible to see the larvae within the colony due to their large size and spherical shape. The larvae are brooded separately from the zooids and are usually a dark pink or purple regardless of the colony colour so stand out and are large enough to see without a hand lens. (Larval information; G. Lambert pers. comm.). The released tadpole larvae have a ring of 25-30 vascular ampullae around the trunk (see image).

This review can be cited as follows:

Emma Snowden 2008. Botrylloides violaceus. A colonial sea squirt. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 22/05/2012]. Available from: <http://www.marlin.ac.uk/speciesinformation.php?speciesID=2791>