Leptomedusae
Encyclopedia
Leptomedusae or Leptomedusa, commonly called thecate hydroids, are a cnidaria
n order
in the subclass
Leptolinae
. They were formerly placed at suborder rank in the paraphyletic "Hydroida
". Their closest living relatives, according to the modern view, are the Anthomedusae
which are similar enough to have always been considered closely related, and the very apomorphic Siphonophora
which were placed outside the "Hydroida" Given that there are no firm rules for synonymy for high-ranked taxa, alternate names like Leptothecata, Thecaphora or Thecata, with or without the ending emended to "-ae", are also often used for the Leptomedusae.
The about 1,900 species
of Leptomedusae are characterized by a number of features: Their polyp
s are always living in colonies with the hydranths set in hydrotheca which are usually permanent and often long enough so the animal can fully retract into it; some have very reduced hydrothecae resembling Anthomedusae
. There is a single whorl
of tentacle
s.
The gonophore
s are borne on much reduced hydranths and usually protected in a peridermal gonotheca. Medusae
forming on fully developed hydranths are extremely rare; usually the gonophores develop into medusae or into sessile sporosacs. The medusae have a shallow bell, bear the gonad
s on their radial canals, and usually have statocyst
s which are formed only from epidermal tissue and more than four tentacles and. The cnidome never has stenoteles.
Notable Leptomedusae include:
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
n order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
in the subclass
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
Leptolinae
Leptolinae
Leptolinae are a cnidarian subclass of the Hydrozoa. They contain the bulk of the paraphyletic "Hydroida" which were one of the main groupings of the Hydrozoa in older classifications and were placed at order rank...
. They were formerly placed at suborder rank in the paraphyletic "Hydroida
Hydroida
Hydroida is an obsolete cnidarian order which united such animals as hydras, hydromedusae, and many marine attached hydroids. However, the group is paraphyletic and not composed from close relatives...
". Their closest living relatives, according to the modern view, are the Anthomedusae
Anthomedusae
Anthomedusae or Anthomedusa, the athecate hydroids, are an order of the Hydrozoa, a class of marine invertebrates belonging to the phylum Cnidaria...
which are similar enough to have always been considered closely related, and the very apomorphic Siphonophora
Siphonophora
Siphonophorae or Siphonophora, the siphonophores, are an order of the Hydrozoa, a class of marine invertebrates belonging to the phylum Cnidaria. They are colonial, but the colonies can superficially resemble jellyfish; although they appear to be a single organism, each specimen is actually a...
which were placed outside the "Hydroida" Given that there are no firm rules for synonymy for high-ranked taxa, alternate names like Leptothecata, Thecaphora or Thecata, with or without the ending emended to "-ae", are also often used for the Leptomedusae.
The about 1,900 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of Leptomedusae are characterized by a number of features: Their polyp
Polyp
A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are approximately cylindrical in shape and elongated at the axis of the body...
s are always living in colonies with the hydranths set in hydrotheca which are usually permanent and often long enough so the animal can fully retract into it; some have very reduced hydrothecae resembling Anthomedusae
Anthomedusae
Anthomedusae or Anthomedusa, the athecate hydroids, are an order of the Hydrozoa, a class of marine invertebrates belonging to the phylum Cnidaria...
. There is a single whorl
Whorl (biology)
In biology, a whorl might occur at the ends of different structures or occur in the middle of structures. It's often used to describe the structures of organs and used in the aid of identification...
of tentacle
Tentacle
A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...
s.
The gonophore
Gonophore
A gonophore is a reproductive organ in Hydrozoa that produces gametes. It is a sporosac, a medusa or any intermediate stage.The name is derived from the Greek words gone and phoreus ....
s are borne on much reduced hydranths and usually protected in a peridermal gonotheca. Medusae
Medusa (biology)
In biology, a medusa is a form of cnidarian in which the body is shaped like an umbrella, in contrast with polyps. Medusae vary from bell-shaped to the shape of a thin disk, scarcely convex above and only slightly concave below...
forming on fully developed hydranths are extremely rare; usually the gonophores develop into medusae or into sessile sporosacs. The medusae have a shallow bell, bear the gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s on their radial canals, and usually have statocyst
Statocyst
The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, echinoderms, cephalopods, and crustaceans. A similar structure is also found in Xenoturbella. The statocyst consists of a sac-like structure containing a mineralised mass and numerous...
s which are formed only from epidermal tissue and more than four tentacles and. The cnidome never has stenoteles.
Notable Leptomedusae include:
- Air fernAir fernNeptune plant or Air fern is a name given to a product that is composed of a species of marine animal called Sertularia argentea, also known as the "sea fir"....
(Sertilaria argentea) of the Sertulariidae, sold dried as novelty "plants" and aquarium ornaments. - Crystal Jelly (Aequorea victoria) of the AequoreidaeAequoreidaeAequoreidae is a hydrozoan family. There are approximately 30 known species found in temperate and tropical marine coastal environments. Aequoreids include Aequorea victoria, the organism from which the green fluorescent protein gene was isolated....
, a bioluminescent hydrozoan. - ObeliaObeliaObelia is a genus in the class Hydrozoa, which consists of mainly marine and some freshwater animal species and have both the polyp and medusa stages in their life cycle...
of the CampanulariidaeCampanulariidaeCampanulariidae is a family of animals in the phylum Cnidaria, or stinging celled animals. Campanulariidae is composed entirely of hydroids, a Greek term meaning "Water Animals" applied to the plant-like polyp colonies of the class Hydrozoa...
Systematics
ORDER LEPTOMEDUSAE- Basal and incertae sedisIncertae sedis, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
- Family Eucopidae
- Suborder ConicaConica (Hydrozoa)Conica are a cnidarian suborder of the Leptomedusae . They make up the bulk of their order; their internal relationships are not well resolved, and most of the roughly 30 families are not yet assigned to a superfamily....
- A large number of uncertain affiliations
- Superfamily Campanulinoidea (disputed)
- Superfamily PlumularioideaPlumularioideaPlumularioidea are one of the few rather robustly established superfamilies of the cnidarian suborder Conica.This superfamily unites about 30 genera in the following families:* Aglaopheniidae Marktanner-Turneretscher, 1890* Halopterididae...
- Superfamily Sertularioidea
- Suborder Proboscidoidea
- Family Bonneviellidae
- Family CampanulariidaeCampanulariidaeCampanulariidae is a family of animals in the phylum Cnidaria, or stinging celled animals. Campanulariidae is composed entirely of hydroids, a Greek term meaning "Water Animals" applied to the plant-like polyp colonies of the class Hydrozoa...
- Family Phialuciidae