''Hydra viridissima'' is a species of
cnidaria
Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.
Their distinguishing feature is cnidocytes, specialized cells that th ...
n which is commonly found in still or slow-moving freshwater
in the Northern temperate zone. ''Hydra viridissima'' is commonly called green hydra due to its coloration, which is due to the
symbiotic
Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...
green algae ''
Chlorella vulgaris
''Chlorella vulgaris'' is a species of green microalga in the division Chlorophyta. It is mainly used as a dietary supplement or protein-rich food additive in Japan.
Description
''C. vulgaris'' is a green Eukaryote, eukaryotic microalga in the ...
'' which live within its body.
These creatures are typically 10 mm long and have tentacles that are about half of their length.
They are strictly carnivorous and typically feed on small crustaceans, insects and annelids. ''Hydra'' are normally sessile and live on aquatic vegetation. They secrete mucous to attach to substrate using their basal disc.
Anatomy
''Hydra'' are multi-cellular organisms. They are made up of two layers of epithelial cells and have a
hypostome
In zoology, the hypostome can refer to structures in distinct animal groups:
*Hypostome (trilobite), the ventral mouthpart plate in trilobites
*Hypostome (tick)
The hypostome (also called the maxilla, radula, or labium) is a calcified harpoo ...
or mouth opening. Circling the mouth are tentacles that contain
nematocyst
A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this ce ...
s or stinging cells to help in prey capture. The mouth and tentacles are called the