Hydrozoa are among the most diverse group of cnidarians. Although marine species vastly outnumber freshwater ones, the genus Hydra may nevertheless be the best known hydrozoan. It appears in almost all textbooks on invertebrate zoology, but this simple animal is not at all representative of the Hydrozoa as a whole, and may actually give a false impression of the complexity of this animal group. For more information see the Hydrozoa Directory.

The Directory includes all extant hydrozoan species and is intended to act as a tool for anyone needing correct taxonomic information, both specialists and non-specialists alike.

The database for this Directory comes from a list of accumulated taxonomic information assembled over the years from the literature of Wim Vervoort and Peter Schuchert (see Schuchert, 1989). The list of the Siphonophorae was provided by Gill Mapstone who also manages the species of this Order. The number of known hydrozoan species is about 3800, although the status of many nominal species is currently unclear. A considerable number of names also represent synonyms.

The list of currently accepted names is at least 90% complete, but the taxonomy of many species still needs revision and newly described species will be added as soon as possible after publication, a task that will be undertaken continuously by the editors. There is currently no broad consensus available for the higher classification of the Hydrozoa and several systems and alternative names are in use. Here, the classification given in Cartwright & Collins (2007) is used, although some minor spelling changes were made. Hence, the classification used in this database is somewhat provisional. The results of ongoing molecular phylogenetic investigations will certainly help to stabilise the taxonomic system in the near future.

No guarantee for the correctness of the data can be given. Please inform the editor responsible for the group of any omissions, errors or typos you come across, or if you need to confirm some crucial data. If you disagree with a synonym, genus assignment or other taxonomic decision, please, send in your reasoned argument to the editors. We will evaluate each contribution and corrections will be incorporated quickly.

Citation

By downloading or consulting data from this website, the visitor acknowledges that he/she agrees to the following:

If data are extracted from this website for secondary analysis resulting in a publication, the website should be cited as follows:

Peter Schuchert (2009). World Hydrozoa database. Available online at http://www.marinespecies.org/hydrozoa. Consulted on 2012-02-06

If any data constitutes a substantial proportion of the records used in secondary analyses (i.e. more than 25% of the data are derived from this source, or the data are essential to arrive at the conclusion of the analysis), the author/manager of the database should be contacted.

References

• Schuchert, P. 1998. How many hydrozoan species are there? Zoologische Verhandelingen 323: 209-219.
• Cartwight, P., & Collins, A. G. 2007. Class Hydrozoa. pp. 153-168 in Daly et al. 2007: Daly, M., Brugler, M. R., Cartwright, P., Collins, A. G., Dawson, M. N., France, S. C., McFadden, C. S., Opresko, D. M., Rodriguez, E., Romano, S., & Stake, J. 2007. The phylum Cnidaria: A review of phylogenetic patterns and diversity 300 years after Linnaeus. Zootaxa 1668: 127-182.

Hydra viridissima

Dynamena pumila

Stylaster roseus

Forskalia edwardsi