The brown hydra, although largely a sessile species is capable of moving by gliding along on the 'basal disc', the part of the body that attaches to the substrate. They may also move by bending the body around, attaching to the substrate with the tentacles, and then 'somersaulting' or 'looping' forwards (3). This species is carnivorous; it feeds on small aquatic invertebrates that are paralysed by the stinging cells when the prey comes into contact with the tentacles. The prey item is then brought to the mouth by the tentacles and taken into the body of the hydra (3). Reproduction in hydras typically takes place asexually by a process known as 'budding', in which a bud-like growth on the body of the 'parent' hydra eventually grows into a new individual that becomes separated from the parent. When conditions are harsh, or there is a shortage of food, hydras can reproduce sexually; a single individual may produce both male and female sex cells, which are released into the water where fertilisation occurs. The egg develops into a larva, which is covered in tiny hair-like structures known as cilia. The larva may either settle immediately and develop into a hydra, or become surrounded in a tough outer layer that allows it to survive harsh conditions (4).

Hydras are freshwater animals that belong to the same group as jellyfish, corals and sea anemones (2). The sac-shaped 'body' is topped with a mouth surrounded by a crown of tentacles that feature stinging cells used to stun prey (2).

The brown hydra is commonly found in the Northern Hemisphere and parts of Australia.

Biogeographic Regions: nearctic (Native ); australian (Native )

The brown hydra is a widespread species, found throughout the northern hemisphere and parts of Australia (3).

Hydras are are well known as the faunas of ponds, spring brooks, unpolluted streams, rivers, and the littoral zone of lakes.

Aquatic Biomes: lakes and ponds; rivers and streams

This hydra is found in freshwater ponds, brooks, rivers, and streams as well as at the edges of lakes, and typically attaches to aquatic plants, stones, twigs and debris (3).

Hydra oligactis, as in all Cnidaria, are strictly carnivorous and eat many different kinds of small metazoans, including annelids, copepods, cladocerans, and insects. Hydra capture their food by paralyzing and killing the food organism by means of nematocysts, which are discharged into the prey. The prey is brought to the mouth (proctostome) by the tentacles, a response that is induced glutathione. This is considered the key mechanism in digestion. The organism is then taken in through the mouth, which is star-shaped or circular. Hydras have been known to feed on the organic material of the substrate when the food supply is insufficient. This behavior, however, is not considered normal. Digestion is both extra and intracellular.

The common asexual method of reproduction by hydras is budding. Buds originate at the junction of the stalk and gastric regions. The bud begins as a hemispherical outpouching that eventually elongates, becomes cylindrical, and develops tentacles. The bud then pinches off and a new individual becomes independent. Buds are produced every two to three days under favorable conditions. Following unfavorable conditions, such as injuries or periods of scarce resources, hydras occasionally reproduce through transverse and longitudinal fission.

The following is a representative barcode sequence, the centroid of all available sequences for this species. 

 
There are 2 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
 

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 2
Species: 2
Species With Barcodes: 1

Common and widespread in Britain (2).

This species is not threatened.

The brown hydra is not listed under any conservation legislation.

Hydra oligactis is a hatchery nuisance because it may kill fish fry.