Editing Gastrotrich (section)

==Reproduction and lifespan==
[[File:Thaumastodermatinae.jpg|thumb|left|''Ptychostomella'' sp., Macrodasyida]]
Gastrotrich reproduction and reproductive behaviour has been little studied. That of [[Macrodasyida|macrodasiyds]] probably most represents that of the ancestral lineage and these more primitive gastrotrichs are simultaneous [[hermaphrodite]]s, possessing both male and female sex organs. There is generally a single pair of [[gonad]]s, the anterior portion of which contains [[sperm]]-producing cells and the posterior portion producing [[ovum|ova]]. The sperm is sometimes packaged in [[spermatophore]]s and is released through male [[gonopore]]s that open, often temporarily, on the underside of the animal, roughly two-thirds of the way along the body. A [[copulatory organ]] on the tail collects the sperm and transfers it to the partner's [[seminal receptacle]] through the female gonopore. Details of the process and the behaviour involved vary with the species, and there is a range of different accessory reproductive organs. During copulation, the "male" individual uses his copulatory organ to transfer sperm to his partner's gonopore and fertilisation is internal. The fertilised eggs are released by rupture of the body wall which afterwards repairs itself. As is the case in most [[protostome]]s, development of the embryo is [[Cleavage (embryo)#Determinate|determinate]], with each cell destined to become a specific part of the animal's body.<ref name=Ruppert/> At least one species of gastrotrich, ''[[Urodasys viviparus]]'', is [[Viviparity|viviparous]].<ref>{{cite journal |author1=Elena, Fregni |author2=Faienza, Maria Grazia |author3=De Zio Grimaldi, Susanna |author4=Tongiorgi, Paolo |author5=Balsamo, Maria |year=1999 |title=Marine gastrotrichs from the Tremiti archipelago in the southern Adriatic Sea, with the description of two new species of ''Urodasys'' |journal=Italian Journal of Zoology |volume= 66|issue=2 |pages=183–194 |doi=10.1080/11250009909356254 |doi-access=free }}</ref>

Many species of chaetotonid gastrotrichs reproduce entirely by [[parthenogenesis]]. In these species, the male portions of the reproductive system are degenerate and non-functional, or, in many cases, entirely absent. Though the eggs have a diameter of less than 50 [[μm]], they are still very large in comparison with the animals' size. Some species are capable of laying eggs that remain [[Dormancy|dormant]] during times of [[desiccation]] or low temperatures; these species, however, are also able to produce regular eggs, which hatch in one to four days, when environmental conditions are more favourable. The eggs of all gastrotrichs undergo [[direct development]] and hatch into miniature versions of the adult. The young typically reach sexual maturity in about three days. In the laboratory, ''[[Lepidodermella squamatum]]'' has lived for up to forty days, producing four or five eggs during the first ten days of life.<ref name=Ruppert/>

Gastrotrichs demonstrate [[eutely]], each species having an invariant genetically fixed number of cells as adults. Cell division ceases at the end of embryonic development and further growth is solely due to cell enlargement.<ref name=Ruppert/>