Discomedusae is a subclass of
jellyfish
Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...
in the class
Scyphozoa
The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish (or "true jellies").
The class name Scyphozoa comes from the Greek word ''skyphos'' (), denoting a kind of drinking cup and alluding to the ...
. It is the sister
taxon
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
of
Coronamedusae. Discomedusae contains about 155 named species and there are likely to be many more as yet undescribed. Jellyfish in this subclass are much more likely to have swarming events or form blooms than those in Coronamedusae.
Discomedusae consists of two
orders
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
,
Rhizostomae
Rhizostomae or Rhizostomeae is an order of jellyfish. Species of this order have neither tentacles nor other structures at the bell's edges. Instead, they have eight highly branched oral arms, along which there are suctorial minimouth orifices. ...
and
Semaeostomeae
Semaeostomeae (literally "flag mouths") is an order of large jellyfish characterized by four long, frilly oral arms flanking their quadrate mouths. The umbrella is domed with scalloped margins, and the gastrovascular system consists of four unbra ...
.
[
]
Rhizostomae
Members of the order Rhizostomae are collectively known as "root-mouth jellies" and are very diverse. They do not have tentacle
In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...
s or other structures at the edge of the bell, instead they have eight oral arms which fuse together to form the manubrium, a central organ with the mouth at its tip, resembling an elephant's trunk. Some have numerous manubrial outgrowths, well-armed with cnidocytes and mucus-secreting cells; others have the central manubrial mouth closed, instead making use of secondary mouths at the side of the manubrium. These adaptations give the jellyfish a large surface area with which to collect large quantities of plankton
Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...
ic organisms. It can trap plankton from the water currents it produces by pulsating.
Semaeostomeae
Members of the Semaeostomeae are known as "flag-mouth jellies" and are large jellyfish. They have an elongate manubrium composed of four oral arms. The edge of the bell bears flaps known as lappets and in the niches between these, there are usually eight rhopalia (sensory organs). Sometimes there are also hollow marginal tentacles. The stomach is subdivided into four gastric pouches, with the four gonads situated on the oral walls of the pouches. Some semaeostomids are suspension feeders, but others supplement this with prey such as small fish, crustaceans, worms and other jellyfish. The pulsating action of the bell is linked by a nerve ring to the sensory inputs received by the rhopalia.[
]
Phylogeny
According to the World Register of Marine Species
The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive list of names of marine organisms.
Content
The content of the registry is edited and maintained by scientific specialist ...
, Discomedusae contains the following taxa:Catostylidae
Catostylidae is a family of jellyfish. Members of this family are characterized by their thick, sausage-like oral arms.
Description
Members of the family Catostylidae are small marine jellyfish with domed bells. The eight short oral arms are bro ...
*** Family Lobonematidae
Lobonematidae is a family of jellyfishes belonging to the order Rhizostomeae.
Genera:
* ''Lobonema'' Mayer, 1910
* ''Lobonemoides
''Lobonemoides'' is a genus of cnidarians belonging to the family Lobonematidae
Lobonematidae is a family of ...
*** Family Lychnorhizidae
*** Family Rhizostomatidae
Rhizostomatidae is a family of cnidarians in the class Scyphozoa.
Genera and species
According to the World Register of Marine Species, 11 extant species are in four extant genera within this family:
*Genus ''Eupilema''
**'' Eupilema inexpect ...
*** Family Stomolophidae
** Suborder Kolpophorae
*** Family Cassiopeidae
*** Family Cepheidae
Cepheidae may refer to:
* Cepheidae (jellyfish)
Cepheidae is a family of jellyfish
Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part o ...
*** Family Mastigiidae
Mastigiidae is a family of true jellyfish. The family is native to the Indo-Pacific, but a species of ''Mastigias'' has been introduced to the West Atlantic, and ''Phyllorhiza punctata'' has been introduced to the West Atlantic and Mediterranea ...
*** Family Thysanostomatidae
Thysanostomatidae is a family of true jellyfish from the Indo-Pacific. The first sighting of ''Thysanostoma loriferum'' in Hong Kong; extending its known range from the Philippines, the Malay Archipelago, and Hawaii; was from the Hong Kong Jelly ...
*** Family Versurigidae
''Versuriga'' is a monotypic genus
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In ...
* Order Semaeostomeae
Semaeostomeae (literally "flag mouths") is an order of large jellyfish characterized by four long, frilly oral arms flanking their quadrate mouths. The umbrella is domed with scalloped margins, and the gastrovascular system consists of four unbra ...
*** Family Cyaneidae
The Cyaneidae are a family of true jellyfish. About 20 species are in this family, including the well-known lion's-mane jellyfish.
Species
The following species are recognized within the family Cyaneidae. Formerly, this family also included th ...
*** Family Drymonematidae
''Drymonema'' is a genus of true jellyfish, placed in its own family, the Drymonematidae. There are three species: '' Drymonema dalmatinum'', '' Drymonema gorgo'', and '' Drymonema larsoni'', which are found in the Gulf of Mexico, Atlantic Ocean ...
*** Family Pelagiidae
The Pelagiidae are a family of jellyfish. Members of the family ''Pelagiidae'' have no ring canal, and the marginal tentacles arise from umbrella margin.
Genera
There are four genera currently recognized:
*Genus ''Chrysaora'' – (14 species)
*G ...
*** Family Phacellophoridae
*** Family Ulmaridae
References
{{Taxonbar, from=Q1413884
Scyphozoa