''Obelia'' is a genus of
hydrozoans, a
class
Class, Classes, or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used d ...
of mainly marine and some freshwater animal
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
that have both
polyp and
medusa stages in their life cycle. Hydrozoa belongs to the
phylum
In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...
Cnidaria
Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...
, which are aquatic (mainly marine) organisms that are relatively simple in structure with a diameter around 1mm.
There are currently 120 known species, with more to be discovered.
These species are grouped into three broad categories: ''O. bidentata'', ''O. dichotoma'', and ''O. geniculata''. ''O. longissima'' was later accepted as a legitimate species, but taxonomy regarding the entire genus is debated over.
''Obelia'' is also called sea fur.
''Obelia'' has a worldwide distribution except the high-Arctic and Antarctic seas. and a stage of ''Obelia'' species are common in coastal and offshore plankton around the world.
[Cornelius, P.F.S., 1995b. North-West European thecate hydroids and their Medusae. Part 2. Synopses of the British Fauna (New Series), No 50.] ''Obelia'' are usually found no deeper than from the water's surface, growing in intertidal rock pools and at the extreme low water of spring tides.
Life cycle
The polyp colony reproduces
asexually. During this stage of life, ''Obelia'' are confined to
substrate surfaces. In mature colonies there are individual
hydranths called