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Trepaxonemata (from ''trepa''-, spiral + axoneme) is a subclass of the Platyhelminthes or flatworms.Ehlers, U. (1985). Das Phylogenetische System der Plathelminthes. Stuttgart: G. Fischer. It includes all parasitic flatworms (clade Neodermata) and several free-living species that were previously grouped in the now obsolete class Turbellaria. Therefore, it contains the majority of species in the
Current classification of Trepaxonemata based on several morphological and molecular studies:
*Subclass Trepaxonemata
**Clade Amplimatricata
***Order
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 ...
Platyhelminthes, excluding the Catenulida, and the Macrostomorpha
Macrostomorpha is a clade of free living flatworms ranked either as class or subclass in the group Rhabditophora. There are about 260 described species in two orders - marine, freshwater and brackish Macrostomida, which group most of the species ...
.
Description
The Trepaxonemata are characterised by: * biflagellate spermatozoa * axoneme of the spermatozoa with a special type of dense core (9+“1” pattern). The axoneme in the spermatozoa of species of Trepaxonemata, also called "trepaxoneme" or "trepaxonematan axoneme" has nine peripheral doublets of microtubules as the usual 9+2 axoneme but the two central microtubules are replaced by a central core. This central core appears as a spiral when seen in longitudinal sections in transmission electron microscopy. This structure is found in all species of Trepaxonemata with very rare exceptions. The trepaxoneme is found only in the Platyhelminthes; no otherphylum
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 ...
has this 9+“1” structure. However, the cilia
The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...
in cells other than spermatozoa in species of Trepaxonemata have the classical 9+2 structure, for example in the epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...
of in protonephridia.
The Trepaxonemata is one of the rare examples of major groups in zoology named after characteristics of spermatozoa, and especially after characteristics observed with transmission electron microscopy.
Systematics
Current classification of Trepaxonemata based on several morphological and molecular studies:
*Subclass Trepaxonemata
**Clade Amplimatricata
***Order Lecithoepitheliata
The Lecithoepitheliata are an order of rhabditophoran flatworms. They are free-living worms, found in freshwater, soil, and marine environments. However, it is still poorly known their roles in the natural food web.
Description
Members of the or ...
***Order Polycladida
**Clade Euneoophora
Trepaxonemata (from ''trepa''-, spiral + axoneme) is a subclass of the Platyhelminthes or flatworms.Ehlers, U. (1985). Das Phylogenetische System der Plathelminthes. Stuttgart: G. Fischer. It includes all parasitic flatworms (clade Neodermata) ...
***Order Rhabdocoela
***Order Proseriata
Proseriata is an order of free-living flatworms in the class Rhabditophora with over 400 species described worldwide.
Description
Proseriate flatworms are minute aquatic organisms, usually with an elongate body. There are no strong synapomorph ...
***Clade Acentrosomata
****Clade Adiaphanida
Trepaxonemata (from ''trepa''-, spiral + axoneme) is a subclass of the Platyhelminthes or flatworms.Ehlers, U. (1985). Das Phylogenetische System der Plathelminthes. Stuttgart: G. Fischer. It includes all parasitic flatworms (clade Neodermata ...
*****Order Prolecithophora
*****Order Fecampiida
Fecampiida is an order of flatworms in the class Rhabditophora. It is a considerably recent clade, erected after molecular studies.
Description
The order Fecampiida, as currently defined, was erected based on molecular studies. They all are pa ...
*****Order Tricladida
****Clade Bothrioneodermata
*****Order Bothrioplanida
*****Clade Neodermata
******Order Trematoda
******Order Monogenea
******Order Cestoda
References
Further reading
* {{open access