Hydra oligactis

Hydra oligactis, also known as the brown hydra, is a species of hydra found widely dispersed in the northern temperate zone. It is a common organism found in still waters from early Spring to late Autumn.

Hydra oligactis
Scientific classification
Kingdom:	Animalia
Phylum:	Cnidaria
Class:	Hydrozoa
Order:	Anthoathecata
Family:	Hydridae
Genus:	Hydra
Species:	H. oligactis
Binomial name
Hydra oligactis Pallas, 1766[1]
Synonyms
Pelmatohydra oligactis (Pallas, 1766)[1] Hydra fusca Linnaeus, 1767[1] Hydra rhaetica Asper, 1879[1] Hydra roeselii Haacke, 1879[1] Hydra rhistica Asper, 1880[1] Hydra monoecia Downing, 1900[1]

It is commonly found attached to the stems of water plants, the undersides of leaves, submerged twigs and on the surface of stones. When disturbed it retracts to a small brown blob which is easily overlooked. Gently sweeping through a clean weedy pond and allowing the collected water and leaves to stand in a jar will often reveal Hydra emerging after only a few minutes.

When in feeding mode, the fully extended tentacles are very long and may exceed 1 inch (25 mm) in length. In this condition the tentacles are very difficult to see with the naked eye and are often only revealed when a prey animal such as Daphnia is caught. The relative length of the tentacles compared to the body is characteristic of the species and serves to differentiate it from any other brown Hydra of cool temperate waters.

References

1. Schuchert, P. (2015). Schuchert P (ed.). "Hydra oligactis Pallas, 1766". World Hydrozoa database. World Register of Marine Species. Retrieved 2015-06-29.