Hydrozoa (hydrozoans; ) are a
taxonomic class
Class 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 differentl ...
of individually very small,
predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
y animals, some solitary and some colonial, most of which inhabit
saline water. The
colonies
In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...
of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few
genera within this class live in
freshwater habitats. Hydrozoans are related to
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- ...
and
coral
Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...
s and belong to the
phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...
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 ...
.
Some examples of hydrozoans are the freshwater jelly (''
Craspedacusta sowerbyi
''Craspedacusta sowerbii'' or peach blossom jellyfish is a species of freshwater hydrozoan jellyfish, or hydromedusa cnidarian. Hydromedusan jellyfish differ from scyphozoan jellyfish because they have a muscular, shelf-like structure called ...
''), freshwater polyps (''
Hydra''), ''
Obelia
''Obelia'' is a genus of hydrozoans, a class of mainly marine and some freshwater animal species that have both polyp and medusa stages in their life cycle. Hydrozoa belongs to the phylum Cnidaria, which are aquatic (mainly marine) organisms t ...
'',
Portuguese man o' war
The Portuguese man o' war (''Physalia physalis''), also known as the man-of-war, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is considered to be the same species as the Pacific man o' war or blue bottle, which is ...
(''Physalia physalis''),
chondrophore
The chondrophores or porpitids are a small group of hydrozoans in the family Porpitidae. Though it derives from an outdated name for this lineage (see below), some still find the term "chondrophore" useful as a synonym to "porpitid" in discussio ...
s (Porpitidae), "
air fern
The air fern (''Sertularia argentea'') is a species of marine animal in the family Sertulariidae. It is also known as the sea fir and Neptune plant.
These so-called "ferns" are dead and dried colonies of hydrozoans, colonies of marine hydroids ...
" (''Sertularia argentea''), and pink-hearted hydroids (''
Tubularia
''Tubularia'' is a genus of hydroids resembling furry pink tufts or balls at the end of long strings, owing to the common names "pink-mouthed" or "pink-hearted" hydroids.
Description
The average height of an individual colony is 40–60  ...
'').
Anatomy
Most hydrozoan species include both a
polypoid and a
medusoid stage in their lifecycles, although a number of them have only one or the other. For example, ''Hydra'' has no medusoid stage, while ''
Liriope'' lacks the
polypoid stage.
Polyps
The hydroid form is usually
not colonial, with multiple polyps connected by tubelike hydrocauli. The hollow cavity in the middle of the polyp extends into the associated hydrocaulus, so that all the individuals of the colony are intimately connected. Where the hydrocaulus runs along the substrate, it forms a horizontal root-like
stolon
In biology, stolons (from Latin '' stolō'', genitive ''stolōnis'' – "branch"), also known as runners, are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external s ...
that anchors the colony to the bottom.
![Tubularia-indivisa](https://upload.wikimedia.org/wikipedia/commons/0/03/Tubularia-indivisa.jpg)
The colonies are generally small, no more than a few centimeters across, but some in
Siphonophorae
Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
can reach sizes of several meters. They may have a tree-like or fan-like appearance, depending on species. The polyps themselves are usually tiny, although some noncolonial species are much larger, reaching , or, in the case of the deep-sea ''
Branchiocerianthus'', a remarkable 2 m (6.6 ft).
[
The hydrocaulus is usually surrounded by a sheath of ]chitin
Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
and proteins called the perisarc. In some species, this extends upwards to also enclose part of the polyps, in some cases including a closeable lid through which the polyp may extend its tentacles.[
In any given colony, the majority of polyps are specialized for feeding. These have a more or less cylindrical body with a terminal mouth on a raised protuberance called the ]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 ...
, surrounded by a number of tentacles. The polyp contains a central cavity, in which initial digestion takes place. Partially digested food may then be passed into the hydrocaulus for distribution around the colony and completion of the digestion process. Unlike some other cnidarian groups, the lining of the central cavity lacks stinging 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, which are found only on the tentacles and outer surface.
All colonial hydrozoans also include some polyps specialized for reproduction. These lack tentacles and contain numerous buds from which the medusoid stage of the lifecycle is produced. The arrangement and type of these reproductive polyps varies considerably between different groups.
In addition to these two basic types of polyps, a few colonial species have other specialized forms. In some, defensive polyps are found, armed with large numbers of stinging cells. In others, one polyp may develop as a large float, from which the other polyps hang down, allowing the colony to drift in open water instead of being anchored to a solid surface.[
]
Medusae
The medusae of hydrozoans are smaller than those of typical jellyfish, ranging from in diameter. Although most hydrozoans have a medusoid stage, this is not always free-living and in many species exists solely as a sexually reproducing bud on the surface of the hydroid colony. Sometimes, these medusoid buds may be so degenerated as to entirely lack tentacles or mouths, essentially consisting of an isolated gonad
A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...
.[
The body consists of a dome-like umbrella ringed by tentacles. A tube-like structure hangs down from the centre of the umbrella and includes the mouth at its tip. Most hydrozoan medusae have just four tentacles, although a number of exceptions exist. Stinging cells are found on the tentacles and around the mouth.
The mouth leads into a central stomach cavity. Four radial canals connect the stomach to an additional, circular canal running around the base of the bell, just above the tentacles. Striated muscle fibres also line the rim of the bell, allowing the animal to move along by alternately contracting and relaxing its body. An additional shelf of tissue lies just inside the rim, narrowing the aperture at the base of the umbrella, and thereby increasing the force of the expelled jet of water.][
The nervous system is unusually advanced for cnidarians. Two nerve rings lie close to the margin of the bell, and send fibres into the muscles and tentacles. The genus '']Sarsia
''Sarsia'' is a genus of hydrozoan in the family Corynidae.
Species
* ''Sarsia angulata'' (Mayer, 1900)
* ''Sarsia apicula'' (Murbach & Shearer, 1902)
* ''Sarsia bella'' Brinckmann-Voss, 2000
* ''Sarsia brachygaster'' Grönberg, 1898
* ''Sarsia ...
'' has even been reported to possess organised ganglia
A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympatheti ...
. Numerous sense organs are closely associated with the nerve rings. Mostly these are simple sensory nerve endings, but they also include statocyst
The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, ctenophorans, echinoderms, cephalopods, and crustaceans. A similar structure is also found in ''Xenoturbella''. The statocyst cons ...
s and primitive light-sensitive ocelli
A simple eye (sometimes called a pigment pit) refers to a form of eye or an optical arrangement composed of a single lens and without an elaborate retina such as occurs in most vertebrates. In this sense "simple eye" is distinct from a multi-l ...
.[
]
Lifecycle
Hydroid colonies are usually dioecious
Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...
, which means they have separate sexes—all the polyps in each colony are either male or female, but not usually both sexes in the same colony. In some species, the reproductive polyps, known as gonozooids (or "gonotheca" in thecate hydrozoans) bud off asexually produced medusae. These tiny, new medusae (which are either male or female) mature and spawn, releasing gamete
A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...
s freely into the sea in most cases. Zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicellula ...
s become free-swimming planula larvae or actinula larvae that either settle on a suitable substrate (in the case of planulae), or swim and develop into another medusa or polyp directly (actinulae). Colonial hydrozoans include siphonophore
Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
colonies, ''Hydractinia
''Hydractinia'' is a genus of commensal athecate hydroids which belong to the family Hydractiniidae. ''Hydractinia'' species mostly live on hermit-crabbed marine gastropod shells.
One species, '' Hydractinia echinata'', is commonly known as s ...
'', ''Obelia
''Obelia'' is a genus of hydrozoans, a class of mainly marine and some freshwater animal species that have both polyp and medusa stages in their life cycle. Hydrozoa belongs to the phylum Cnidaria, which are aquatic (mainly marine) organisms t ...
'', and many others.[Bouillon, J.; Gravili, C.; Pagès, F.; Gili, J.-M.; Boero, F. (2006). An introduction to Hydrozoa. Mémoires du Muséum national d'Histoire naturelle, 194. Muséum national d'Histoire naturelle: Paris, France. . 591pp. + 1 cd-rom]
In hydrozoan species with both polyp and medusa generations, the medusa stage is the sexually reproductive phase. Medusae of these species of Hydrozoa are known as "hydromedusae". Most hydromedusae have shorter lifespans than the larger scyphozoan jellyfish. Some species of hydromedusae release gametes shortly after they are themselves released from the hydroids (as in the case of fire coral
Fire corals (''Millepora'') are a genus of colonial marine organisms that exhibit physical characteristics similar to that of coral. The name coral is somewhat misleading, as fire corals are not true corals but are instead more closely related ...
s), living only a few hours, while other species of hydromedusae grow and feed in the 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 ...
for months, spawning daily for many days before their supply of food or other water conditions deteriorate and cause their demise.
Additionally, some hydrozoan species (particularly in Turritopsis
''Turritopsis'' is a genus of hydrozoans in the family Oceaniidae.
Species
According to the '' World Register of Marine Species'', this genus includes the following species:
* '' Turritopsis chevalense'' – ''species inquirenda''
* ''Turrito ...
genus) share an unusual life cycle among the animals - they can transform themselves from sexually mature medusae stage back to their juvenile hydroid stage.
Systematics and evolution
The earliest hydrozoans may be from the Vendian
The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the ...
(late Precambrian), more than 540 million years ago.
Hydrozoan systematics
Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic tre ...
are highly complex. Several approaches for expressing their interrelationships were proposed and heavily contested since the late 19th century, but in more recent times a consensus seems to be emerging.
Historically, the hydrozoans were divided into a number of orders, according to their mode of growth and reproduction. Most famous among these was probably the assemblage called "Hydroida
Hydroidolina is a subclass of Hydrozoa and makes up 90% of the class. Controversy surrounds who the sister groups of Hydroidolina are, but research has shown that three orders remain consistent as direct relatives: Siphonophorae, Anthoathecata, an ...
", but this group is apparently paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
, united by plesiomorph
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorphy, apomorphy, and ...
ic (ancestral) traits. Other such orders were the Anthoathecatae, Actinulidae
Actinulida are an order of hydrozoans in the subclass Trachylinae
Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedus ...
, Laingiomedusae
Anthoathecata, or the athecate hydroids, are an order (biology), order of hydrozoans belonging to the phylum (biology), phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular grou ...
, Polypodiozoa, Siphonophorae
Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
and Trachylina
Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedusae, Trachymedusae, the Actinulidae, then considered an independent orde ...
.
As far as can be told from the molecular
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
and morphological data at hand, the Siphonophora for example were just highly specialized "hydroids," whereas the Limnomedusae
Limnomedusae is an order of hydrozoans.
Taxonomy
The taxon was erected by Danish marine biologist Paul Lassenius Kramp in 1938 to accommodate certain families of hydrozoans with biphasic life histories. It includes genera with medusae with ect ...
—presumed to be a "hydroid" suborder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
—were simply very primitive hydrozoans and not closely related to the other "hydroids." So, the hydrozoans now are at least tentatively divided into two subclasses, the Leptolinae
Hydroidolina is a subclass of Hydrozoa and makes up 90% of the class. Controversy surrounds who the sister groups of Hydroidolina are, but research has shown that three orders remain consistent as direct relatives: Siphonophorae, Anthoathecata, ...
(containing the bulk of the former "Hydroida" and the Siphonophora) and the Trachylinae
Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedusae, Trachymedusae, the Actinulidae, then considered an independent orde ...
, containing the others (including the Limnomedusae). The monophyly
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...
of several of the presumed orders in each subclass is still in need of verification.
In any case, according to this classification, the hydrozoans can be subdivided as follows, with 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 ...
names emended to end in "-ae":
Class Hydrozoa
* Subclass Hydroidolina
Hydroidolina is a subclass of Hydrozoa and makes up 90% of the class. Controversy surrounds who the sister groups of Hydroidolina are, but research has shown that three orders remain consistent as direct relatives: Siphonophorae, Anthoathecata, an ...
** Order Anthoathecata
Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular group. It has also been called Gymnobl ...
(= Anthoathecata(e), Athecata(e), Anthomedusae, Stylasterina(e)) — includes Laingoimedusae but monophyly requires verification
** Order Leptothecata
Leptothecata, or thecate hydroids, are an order of hydrozoans in the phylum Cnidaria. Their closest living relatives are the athecate hydroids, which are similar enough to have always been considered closely related, and the very apomorphic Siph ...
(= Leptothecata(e), Thecaphora(e), Thecata(e), Leptomedusae)
** Order Siphonophorae
Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
* Subclass Trachylinae
Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedusae, Trachymedusae, the Actinulidae, then considered an independent orde ...
** Order Actinulidae
Actinulida are an order of hydrozoans in the subclass Trachylinae
Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedus ...
** Order Limnomedusae
Limnomedusae is an order of hydrozoans.
Taxonomy
The taxon was erected by Danish marine biologist Paul Lassenius Kramp in 1938 to accommodate certain families of hydrozoans with biphasic life histories. It includes genera with medusae with ect ...
— monophyly requires verification; tentatively placed here
** Order Narcomedusae
Narcomedusae is an order of hydrozoans in the subclass Trachylinae. Members of this order do not normally have a polyp stage. The medusa has a dome-shaped bell with thin sides. The tentacles are attached above the lobed margin of the bell with ...
** Order Trachymedusae
Trachymedusae belong to the phylum Cnidaria and the class Hydrozoa, among the 30 genera are 5 families containing around 50 species in all, the family Rhopalonematidae has the greatest diversity.
Description
Trachymedusae are identifiable by the ...
— monophyly requires verification
ITIS
The Integrated Taxonomic Information System (ITIS) is an American partnership of federal agencies designed to provide consistent and reliable information on the taxonomy of biological species. ITIS was originally formed in 1996 as an interagenc ...
uses the same system, but unlike here, does not use the oldest available names for many groups.
In addition, there exists a cnidarian parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
, ''Polypodium hydriforme
''Polypodium'' is a genus of cnidarians that parasitizes in the eggs of sturgeon and similar fishes ( Acipenseridae and Polyodontidae). It is one of the few metazoans (animals) that live inside the cells of other animals.
''Polypodium hydri ...
'', which lives inside its host's cell
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...
s. It is sometimes placed in the Hydrozoa, though its relationships are currently unresolved—a somewhat controversial 18S rRNA sequence
In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is calle ...
analysis found it to be closer to the also parasitic Myxozoa
Myxozoa (etymology: Greek: μύξα ''myxa'' "slime" or "mucus" + thematic vowel o + ζῷον ''zoon'' "animal") is a subphylum of aquatic cnidarian animals – all obligate parasites. It contains the smallest animals ever known to have lived. O ...
n. It was traditionally placed in its own class
Class 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 differentl ...
, Polypodiozoa, and this view is often seen to reflect the uncertainties surrounding this highly distinct animal.[Zrzavý & Hypša 2003]
Other classifications
Some of the more widespread classification systems for the Hydrozoa are listed below. Though they are often found in seemingly authoritative Internet sources and databases, they do not agree with the available data. Especially the presumed phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
distinctness of the Siphonophorae
Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
is a major flaw that was corrected only recently.
The obsolete classification mentioned above was:
* Order Actinulidae
Actinulida are an order of hydrozoans in the subclass Trachylinae
Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedus ...
* Order Anthoathecatae
* Order Hydroida
Hydroidolina is a subclass of Hydrozoa and makes up 90% of the class. Controversy surrounds who the sister groups of Hydroidolina are, but research has shown that three orders remain consistent as direct relatives: Siphonophorae, Anthoathecata, an ...
** Suborder Anthomedusae
Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular group. It has also been called Gymnobl ...
** Suborder Leptomedusae
Leptothecata, or thecate hydroids, are an order of hydrozoans in the phylum Cnidaria. Their closest living relatives are the athecate hydroids, which are similar enough to have always been considered closely related, and the very apomorphic Sipho ...
** Suborder Limnomedusae
Limnomedusae is an order of hydrozoans.
Taxonomy
The taxon was erected by Danish marine biologist Paul Lassenius Kramp in 1938 to accommodate certain families of hydrozoans with biphasic life histories. It includes genera with medusae with ect ...
* Order Laingiomedusae
Anthoathecata, or the athecate hydroids, are an order (biology), order of hydrozoans belonging to the phylum (biology), phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular grou ...
* Order Polypodiozoa
* Order Siphonophorae
Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
* Order Trachylina
Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedusae, Trachymedusae, the Actinulidae, then considered an independent orde ...
** Suborder Narcomedusae
Narcomedusae is an order of hydrozoans in the subclass Trachylinae. Members of this order do not normally have a polyp stage. The medusa has a dome-shaped bell with thin sides. The tentacles are attached above the lobed margin of the bell with ...
** Suborder Trachymedusae
Trachymedusae belong to the phylum Cnidaria and the class Hydrozoa, among the 30 genera are 5 families containing around 50 species in all, the family Rhopalonematidae has the greatest diversity.
Description
Trachymedusae are identifiable by the ...
A very old classification that is sometimes still seen is:
* Order Hydroida
Hydroidolina is a subclass of Hydrozoa and makes up 90% of the class. Controversy surrounds who the sister groups of Hydroidolina are, but research has shown that three orders remain consistent as direct relatives: Siphonophorae, Anthoathecata, an ...
* Order Milleporina
Fire corals (''Millepora'') are a genus of colonial marine organisms that exhibit physical characteristics similar to that of coral. The name coral is somewhat misleading, as fire corals are not true corals but are instead more closely related ...
* Order Siphonophorae
Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
* Order Stylasterina
Anthoathecata, or the athecate hydroids, are an order (biology), order of hydrozoans belonging to the phylum (biology), phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular grou ...
(= Anthomedusae)
* Order Trachylinida
Catalogue of Life
The Catalogue of Life is an online database that provides an index of known species of animals, plants, fungi, and microorganisms. It was created in 2001 as a partnership between the global Species 2000 and the American Integrated Taxonomic Info ...
uses:
* Order Actinulida
Actinulida are an order of hydrozoans in the subclass Trachylinae
Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedusa ...
* Order Anthoathecata
Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular group. It has also been called Gymnobl ...
(= Anthomedusae)
* Order Hydroida
Hydroidolina is a subclass of Hydrozoa and makes up 90% of the class. Controversy surrounds who the sister groups of Hydroidolina are, but research has shown that three orders remain consistent as direct relatives: Siphonophorae, Anthoathecata, an ...
* Order Laingiomedusae
Anthoathecata, or the athecate hydroids, are an order (biology), order of hydrozoans belonging to the phylum (biology), phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular grou ...
* Order Leptothecata
Leptothecata, or thecate hydroids, are an order of hydrozoans in the phylum Cnidaria. Their closest living relatives are the athecate hydroids, which are similar enough to have always been considered closely related, and the very apomorphic Siph ...
(= Leptomedusae)
* Order Limnomedusae
Limnomedusae is an order of hydrozoans.
Taxonomy
The taxon was erected by Danish marine biologist Paul Lassenius Kramp in 1938 to accommodate certain families of hydrozoans with biphasic life histories. It includes genera with medusae with ect ...
* Order Narcomedusae
Narcomedusae is an order of hydrozoans in the subclass Trachylinae. Members of this order do not normally have a polyp stage. The medusa has a dome-shaped bell with thin sides. The tentacles are attached above the lobed margin of the bell with ...
* Order Siphonophorae
Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
* Order Trachymedusae
Trachymedusae belong to the phylum Cnidaria and the class Hydrozoa, among the 30 genera are 5 families containing around 50 species in all, the family Rhopalonematidae has the greatest diversity.
Description
Trachymedusae are identifiable by the ...
Animal Diversity Web
Animal Diversity Web (ADW) is an online database that collects the natural history, classification, species characteristics, conservation biology, and distribution information on thousands of species of animals. The website includes thousands ...
uses:
* Order Actinulida
Actinulida are an order of hydrozoans in the subclass Trachylinae
Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedusa ...
* Order Anthoathecata
Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular group. It has also been called Gymnobl ...
* Order Laingiomedusae
Anthoathecata, or the athecate hydroids, are an order (biology), order of hydrozoans belonging to the phylum (biology), phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular grou ...
* Order Leptothecata
Leptothecata, or thecate hydroids, are an order of hydrozoans in the phylum Cnidaria. Their closest living relatives are the athecate hydroids, which are similar enough to have always been considered closely related, and the very apomorphic Siph ...
* Order Limnomedusae
Limnomedusae is an order of hydrozoans.
Taxonomy
The taxon was erected by Danish marine biologist Paul Lassenius Kramp in 1938 to accommodate certain families of hydrozoans with biphasic life histories. It includes genera with medusae with ect ...
* Order Narcomedusae
Narcomedusae is an order of hydrozoans in the subclass Trachylinae. Members of this order do not normally have a polyp stage. The medusa has a dome-shaped bell with thin sides. The tentacles are attached above the lobed margin of the bell with ...
* Order Siphonophorae
Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
* Order Trachymedusae
Trachymedusae belong to the phylum Cnidaria and the class Hydrozoa, among the 30 genera are 5 families containing around 50 species in all, the family Rhopalonematidae has the greatest diversity.
Description
Trachymedusae are identifiable by the ...
References
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* (2003): Myxozoa, ''Polypodium'', and the origin of the Bilateria: The phylogenetic position of "Endocnidozoa" in light of the rediscovery of ''Buddenbrockia''. ''Cladistics'' 19(2): 164–169. (HTML abstract)
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Medusozoa