''Hydra oligactis'', also known as the brown hydra, is a species of
hydra
Hydra generally refers to:
* Lernaean Hydra, a many-headed serpent in Greek mythology
* ''Hydra'' (genus), a genus of simple freshwater animals belonging to the phylum Cnidaria
Hydra or The Hydra may also refer to:
Astronomy
* Hydra (constel ...
found widely dispersed in the northern
temperate zone. It is a common organism found in still waters from early Spring to late Autumn.
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 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.
When a cold sensitive strain of ''H. oligactis'' is subjected to temperature stress, it undergoes a shift from asexual budding to
sexual reproduction. This shift involves an upreglation of genes involved in
gametogenesis,
cellular senescence
Cellular senescence is a phenomenon characterized by the cessation of cell division. In their experiments during the early 1960s, Leonard Hayflick and Paul Moorhead found that normal human fetal fibroblasts in culture reach a maximum of approxi ...
,
apoptosis
Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...
and
DNA repair, and a downregulation of genes involved in
stem cell
In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type o ...
maintenance.
''Hydra oligactis'' is preyed upon by the flatworm ''Microstomum lineare'', which incorporates ''Hydra'' stenoteles into its own epidermis.
References
Hydridae
Animals described in 1766
Taxa named by Peter Simon Pallas
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