Star ascidian |  |
Botryllus schlosseri
(Pallas, 1766)
Karen Gowlett-Holmes, CSIRO Marine Research
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Taxonomy |
| Phylum: |
Chordata |
| Subphylum: |
Tunicata |
| Class: |
Ascidiacea |
| Order: |
Pleurogona |
| Suborder: |
Stolidobranchia |
| Family: |
Styelidae |
| Genus: |
Botryllus |
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Description |
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Botryllus schlosseri is an colonial ascidian composed of many individual asexually produced zooids arranged in clusters. Colonies vary in size and shape from sheets to stalked or sessile, fleshy lobes. Colour is variable from purple or brown to colourless tests with yellow, white or orange zooids. The 3 mm long zooids are arranged in circular or elongate flower-like clusters, with all zooids in a cluster sharing a large, circular opening - an exhalant siphon. Spherical ampullae (small bumps) occur in the test between the zooids and become more elongate at the edges of the colony. Internally, the inhalant siphon (atrial aperture) is small, the body wall forming a broad siphon, with a small lip on the upper border of the opening.
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Diagram |
Diagram: Kott, 1985
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Similar Species |
Sarcobotrylloides racemosum Hartmeyer, 1912
Botrylloides racemosum Quoy & Gaimard, 1834
Botrylloides violaceum Oka, 1927
MORE (Common Names, Synonyms, Identification Notes, Similar Species, Morphology)...
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Reproduction and Growth |
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B. schlosseri is a cyclical hermaphrodite. All zooids undergo an asexual and sexual cycle. A new generation of zooids form by asexual budding of the sides of existing zooids. These buds become functional and replace previous zooid generations, which are resorbed. Sexual reproduction then occurs with internal fertilisation of mature eggs, soon after the inhalant siphons open. Sperm release begins 16 hours later, avoiding self-fertilisation. Developing embryos are brooded and released as free-swimming larvae just before zooids degenerate. Larvae settle and metamorphose into a new colony. MORE (Reproduction, Life Cycle)...
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Habitat |
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Colonies of B. schlosseri are encrusting and are found attached to rocks, algae, seagrass, other fouling organisms, floats, wharf pylons, vessel hulls and other submerged man-made structures. It is mainly recorded from temperate waters, but occurs in sub-tropical locations in the Mediterranean and Australia. Colonies are found from the very shallow subtidal to almost 200m depth. MORE (Habitat, Survival)...
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Feeding Preferences |
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Trophic status: Suspension Feeder B. schlosseri feeds on suspended matter such as phytoplankton, zooplankton and organic materials.
MORE (Food, Competitors)...
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Predators |
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Colonies of B. schlosseri are eaten by crabs, gastropods, nudibranchs and flatworms.
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Impacts |
Colonies of B. schlosseri are encrusting and can overgrow other fouling organisms altering community dynamics as well as occurring as nuisance fouling on vessel hulls, floats, aquaculture equipment and species (such as oysters) and other submerged man-made structures.
MORE (Impact information)...
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Vectors |
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Control Options |
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Additional Information |
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MORE (Other additional information available) ...
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Key ReferencesKott, P. (1985). The Australian Ascidiacea. Part 1: Phlebobranchia and Stolidobranchia. Memoirs of the Queensland Museum 23:1-438.Milkman, R. (1967). Genetic and developmental studies on Botryllus schlosseri. Biological Bulletin 132:229-243. Millar, R.H. (1971). The biology of ascidians. Advances in Marine Biology 9:1-100. Osman, R.W., Whitlatch, R.B., Malatesta, R.J. (1992). Potential role of micro-predators in determining recruitment into a marine community. Marine Ecology Progress Series 83:35-43. Stewart-Savage, J., Wagstaff, B.J., Yund, P.O. (1999). Developmental basis of phenotypic variation in egg production in a colonial ascidian: Primary oocyte production versus oocyte development. Biological Bulletin 196:63-69. Yund, P.O. (1998). The effect of sperm competition on male gain curves in a colonial marine invertebrate. Ecology 79(1):328-339. Yund, P.O., McCartney, M.A. (1994). Male reproductive success in sessile invertebrates: Competition for fertilizations. Ecology 75:2151-2167. |
| MORE - References... |