Clavopsella navis
Phylum: Cnidaria
Class: Hydrozoa
Order: Athecata
Species name: Clavopsella navis (Millard 1959)
Synonyms: Clavopsella quadrangularia Thiel 1962, Rhizorhagium navis   Millard 1959
Common name: None
 
Date of introduction and origin
Clavopsella navis was first noted in 1973 (P.F.S. Cornelius pers. comm.) in Widewater Lagoon, Shoreham, West Sussex. Its origin is not known since it has only ever been found in the vicinity of ports and harbours, presumably as an introduction.
 
Method of introduction
It was probably transported on ships' hulls.
 
Reasons for success
Many hydroids are substrate generalists which probably assists in their distribution on ships and other slow-moving material as well as establishment upon arrival in foreign ports etc.
 
Rate of spread and methods involved
In Britain, C. navis is not known to have spread outside the one lagoon where it is found.
 
Distribution
Widewater Lagoon, West Sussex, contains the only known British population. Elsewhere in Europe it is known from the Kiel Canal, Germany, and the Azores. Outside Europe, it is only known from Cape Town harbour, South Africa (Barnes 1994). It is a brackish-water species.
 
Factors likely to influence spread and distribution
Its spread is likely to be influenced by slow-moving shipping entering brackish waters.
 
Effects on the environment
Unknown.
 
Effects on commercial interests
Unknown.
 
Control methods used and effectiveness
None used.
 
Beneficial effects
None known.
 
Comments
None.
 
References
Barnes, R.S.K. 1994. The brackish-water fauna of northwestern Europe. Cambridge, Cambridge University Press.
 
Millard, N.A.H. 1959. Hydrozoa from ships' hulls and experimental plates in Cape Town docks. Annals of the South African Museum, 45:239-256.
 
Millard, N.A.H. 1975. Monograph on the Hydroida of southern Africa. Annals of the South African Museum, 68. (pp.100-102)
 
Acknowledgements (contributions from questionnaire)
Dr P.F.S. Cornelius, The Natural History Museum, London.