| Lecithoepitheliata | |
|---|---|
 | |
| Geocentrophora baltica | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Platyhelminthes |
| Clade: | Amplimatricata |
| Order: | Lecithoepitheliata Reisinger, 1924 |
| Families | |
The Lecithoepitheliata are an order of rhabditophoran flatworms. They are free-living worms, found in freshwater, soil, [1] and marine environments. [2] However, it is still poorly known their roles in the natural food web. [3]
Members of the order Lecithoepitheliata are distinguished from other flatworms by the presence of four nerve cords and the fact that the ovary forms a single structure that produces both the eggs (ovocytes) and nourishing yolk cells (vitellocytes). [4] The vitellocytes form a follicle around the ovocyte, hence the name of the group, which means "with a yolk epithelium". In most other rhabditophorans, yolk cells, where present at all, are typically formed in glands derived from the ovaries, but separate from them, called vitellaria. [5] Other diagnostic features of this order include the presence of a sharp stylet on the end of the penis, and a simple, unbranched, intestine. The penis lacks a proper pore and is protruded through the mouth. [4]
The order Lecithoepitheliata is usually classified as belonging to the clade Neoophora, a subgroup of rhabditophoran flatworms distinguished by the presence of ectolecithal eggs, i.e., yolk is stored outside the ovocytes. [6] However, recent molecular studies have grouped Lecithoepitheliata (at least the family Prorrhynchidae) with the order Polycladida, which has endolecithal eggs, i.e., yolk is stored inside the ovocytes as in most animals. [5] Another previous study, which included representatives of both families of Lecithoepitheliata, concluded that Prorhynchidae is the basalmost clade of Neoophora, followed by Gnosonesimidae. In the former scenario, the ectolecithal condition would have evolved independently twice, and in the latter it would have arisen only once, but Lecithoepitheliata would be paraphyletic. [7]
Phylogeny of Lecithoepitheliata in relation to other rhabditophorans according to Laumer & Giribet (2011): [7]
| Rhabditophora |
| ||||||||||||||||||||||||
Phylogeny according to Egger et al. (2015): [5]
| Rhabditophora |
| ||||||||||||||||||
The flatworms, flat worms, Platyhelminthes, or platyhelminths are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. Unlike other bilaterians, they are acoelomates, and have no specialised circulatory and respiratory organs, which restricts them to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. The digestive cavity has only one opening for both ingestion and egestion ; as a result, the food cannot be processed continuously.
Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of 1300 known species. Most ribbon worms are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. Many have patterns of yellow, orange, red and green coloration. The foregut, stomach and intestine run a little below the midline of the body, the anus is at the tip of the tail, and the mouth is under the front. A little above the gut is the rhynchocoel, a cavity which mostly runs above the midline and ends a little short of the rear of the body. All species have a proboscis which lies in the rhynchocoel when inactive but everts to emerge just above the mouth to capture the animal's prey with venom. A highly extensible muscle in the back of the rhynchocoel pulls the proboscis in when an attack ends. A few species with stubby bodies filter feed and have suckers at the front and back ends, with which they attach to a host.
Parazoa are a taxon with sub-kingdom category that is located at the base of the phylogenetic tree of the animal kingdom in opposition to the sub-kingdom Eumetazoa; they group together the most primitive forms, characterized by not having proper tissues or that, in any case, these tissues are only partially differentiated. They generally group a single phylum, Porifera, which lack muscles, nerves and internal organs, which in many cases resembles a cell colony rather than a multicellular organism itself. All other animals are eumetazoans, which do have differentiated tissues.
The Turbellaria are one of the traditional sub-divisions of the phylum Platyhelminthes (flatworms), and include all the sub-groups that are not exclusively parasitic. There are about 4,500 species, which range from 1 mm (0.039 in) to large freshwater forms more than 500 mm (20 in) long or terrestrial species like Bipalium kewense which can reach 600 mm (24 in) in length. All the larger forms are flat with ribbon-like or leaf-like shapes, since their lack of respiratory and circulatory systems means that they have to rely on diffusion for internal transport of metabolites. However, many of the smaller forms are round in cross section. Most are predators, and all live in water or in moist terrestrial environments. Most forms reproduce sexually and with few exceptions all are simultaneous hermaphrodites.
Acoelomorpha is a subphylum of very simple and small soft-bodied animals with planula-like features which live in marine or brackish waters. They usually live between grains of sediment, swimming as plankton, or crawling on other organisms, such as algae and corals. With the exception of two acoel freshwater species, all known Acoelomorphs are marine.
The Polycladida represents a highly diverse clade of free-living marine flatworms. They are known from the littoral to the sublittoral zone, and many species are common from coral reefs. Only a few species are found in freshwater habitats.
Pseudocerotidae is a family of flatworms which includes the Bedford's flatworm. Pseudocerotidae are simple organisms categorized by their oval bodies and tentacles and bright colors. They use the cilia to glide along surfaces. Most commonly referred to as marine flatworms, closely related to the orders Macrostomorpha and Lecithoepitheliata. These organisms have very complex reproductive systems, no blood systems or organs for gas exchange, a simple brain and are hermaphroditic.
Vetigastropoda is a major taxonomic group of sea snails, marine gastropod mollusks that form a very ancient lineage. Taxonomically the Vetigastropoda are sometimes treated as an order, although they are treated as an unranked clade in Bouchet and Rocroi, 2005.
The Spiralia are a morphologically diverse clade of protostome animals, including within their number the molluscs, annelids, platyhelminths and other taxa. The term Spiralia is applied to those phyla that exhibit canonical spiral cleavage, a pattern of early development found in most members of the Lophotrochozoa.
Dugesiidae is a family of freshwater planarians distributed worldwide. The type genus is Dugesia Girard, 1850.
Neoophora is a group of rhabditophoran flatworms with ectolecithal eggs, i.e., yolk is not present in the egg as in most animals, but rather is secreted by accessory glands called vitellaria or yolk glands. These glands have the same embryonic origin as the ovaries, but usually constitute a separate organ in adult animals.
Obama is a genus of land planarians from South America. It contains several species adapted to human-disturbed environments, including the only invasive land planarian native to the Neotropical realm, Obama nungara, which has been accidentally introduced in Europe.
The reproductive system of planarians is broadly similar among different families, although the associated structures can vary in complexity.
Neodermata is a clade of rhabditophoran flatworms containing the parasitic groups Trematoda, Monogenea and Cestoda.
Rhynchodeminae is a subfamily of land planarians with a worldwide distribution.
Rhabditophora is a class of flatworms. It includes all parasitic flatworms and most free-living species that were previously grouped in the now obsolete class Turbellaria. Therefore, it contains the majority of the species in the phylum Platyhelminthes, excluding only the catenulids, to which they appear to be the sister group.
Rhabdocoela is an order of flatworms in the class Rhabditophora with about 1700 species described worldwide. The order was first described in 1831 by Christian Gottfried Ehrenberg. Most of rhabdocoels are free-living organisms, but some live symbiotically with other animals.
Trepaxonemata is a subclass of the Platyhelminthes or flatworms. It includes all parasitic flatworms and several free-living species that were previously grouped in the now obsolete class Turbellaria. Therefore, it contains the majority of species in the phylum Platyhelminthes, excluding the Catenulida, and the Macrostomorpha.
Dalytyphloplanida is a suborder of rhabdocoel flatworms. It contains about 1000 species and has a cosmopolitan distribution in both marine and freshwater environments, with several groups having commensal or parasitic lifestyles.
Pseudoceros canadensis, commonly known as the Puget flatworm, is a species of free-living flatworm in the genus Pseudoceros, belonging to the family Pseudocerotidae.
{{cite journal}}: Cite journal requires |journal= (help)  | This flatworm- (or platyhelminth-) related article is a stub. You can help Wikipedia by expanding it. |