Lecithoepitheliata

{{Automatic taxobox

| image = Geocentrophora baltica.jpg

| image_caption = Geocentrophora baltica

| taxon = Lecithoepitheliata

| authority = Reisinger, 1924

| subdivision_ranks = Families

| subdivision =

}}

The Lecithoepitheliata are an order of rhabditophoran flatworms. They are free-living worms, found in freshwater, soil,{{cite journal | last1 = Adl| first1 = Sina M. | year = 2006 |title = Observations on a Geocentrophora sp. (Lecithoepitheliata) flatworm from forest soils in Nova Scotia | publisher = Journal of Natural History 40(23-24) | page = 1381 }} and marine environments.{{cite book | last1 = Barnes | first1 = Robert D. | year = 1982 |title = Invertebrate Zoology |publisher = Holt-Saunders International | location= Philadelphia, PA | page = 229 | isbn = 0-03-056747-5}} However, it is still poorly known their roles in the natural food web.{{cite journal |last1=Adl |first1=Sina M. |last2=Ruiz‐Trillo |first2=Inaki |last3=Wilson |first3=Melanie L. |title=Observations on a Geocentrophora sp. (Lecithoepitheliata) flatworm from forest soils in Nova Scotia |journal=Journal of Natural History |date=18 October 2006 |volume=40 |issue=23–24 |pages=1381–1387 |doi=10.1080/00222930600929285 |s2cid=85892208 |url=https://www.tandfonline.com/doi/abs/10.1080/00222930600929285 |access-date=13 February 2023}}

Description

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).{{cite journal | last1 = Schockaert | first1 = Ernest R. | last2 = Hooge | first2 = Matthew | last3 = Sluys | first3 = Ronald | last4 = Schilling | first4 = Steve| last5 = Tyler | first5 = Seth | last6 = Artois | first6 = Tom | title = Global diversity of free living flatworms (Platyhelminthes, "Turbellaria") in freshwater | journal = Hydrobiologia | volume = 595 | issue = 1 | year = 2007 | pages = 41–48 | issn = 0018-8158 | doi = 10.1007/s10750-007-9002-8| s2cid = 21471933 }} 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.{{Cite journal | doi = 10.1016/j.cub.2015.03.034 | last1 = Egger | first1 = B. | last2 = Lapraz | first2 = F. | last3 = Tomiczek | first3 = B. | last4 = Müller | first4 = S. | last5 = Dessimoz | first5 = C. | last6 = Girstmair | first6 = J. | last7 = Škunca | first7 = N. | last8 = Rawlinson | first8 = K. A. | last9 = Cameron | first9 = C. B. | last10 = Beli | first10 = E. | last11 = Todaro | first11 = M. A. | last12 = Gammoudi | first12 = M. | last13 = Noreña | first13 = C. | last14 = Telford | first14 = M. I. | date = 2015 | title = A Transcriptomic-Phylogenomic Analysis of the Evolutionary Relationships of Flatworms | journal = Current Biology | volume = 25 | issue = 10 | pages = 1347–1353| pmc = 4446793 | pmid=25866392}} 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.

Phylogeny

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.{{cite journal |last1=Williams |first1=Joan Bowman |title=Ultrastructural studies on Kronborgia (Platyhelminthes; Neoophora): The spermatozoon |journal=International Journal for Parasitology |date=June 1988 |volume=18 |issue=4 |pages=477–483 |doi=10.1016/0020-7519(88)90010-0 |url=https://www.sciencedirect.com/science/article/abs/pii/0020751988900100 |access-date=13 February 2023|url-access=subscription }} 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. 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.{{cite journal | last1 = Laumer | first1 = Christopher E. | last2 = Giribet | first2 = Gonzalo | title = Inclusive taxon sampling suggests a single, stepwise origin of ectolecithality in Platyhelminthes | journal = Biological Journal of the Linnean Society | volume = 111 | issue = 3 | year = 2014 | pages = 570–588 | issn = 0024-4066 | doi = 10.1111/bij.12236| doi-access = free }}

Phylogeny of Lecithoepitheliata in relation to other rhabditophorans according to Laumer & Giribet (2011):

{{clade | style = font-size:100%;line-height:80%

|label1 = Rhabditophora

|1={{Clade

|1=Polycladida

|2={{Clade

|1=Macrostomorpha

|label2=Neoophora

|2={{Clade

|1=Prorhynchidae (Lecithoepitheliata)

|2={{Clade

|1=Gnosonesimidae (Lecithoepitheliata)