Editing Sex-determination system (section)

===Other environmental systems===
There are other [[environmental sex determination]] systems including location-dependent determination systems as seen in the marine worm ''[[Bonellia viridis]]'' – larvae become males if they make physical contact with a female, and females if they end up on the bare sea floor. This is triggered by the presence of a chemical produced by the females, [[Bonellia viridis#Bonnelin as a biocide|bonellin]].<ref name="Gilbert-2006">{{cite book | vauthors = Gilbert S |title=Developmental biology |url=https://archive.org/details/developmentalbio00gilb_292 |url-access=limited |date=2006 |publisher=Sinauer Associates, Inc. Publishers |location=Sunderland, Mass. |isbn=9780878932504 |pages=[https://archive.org/details/developmentalbio00gilb_292/page/n569 550]–553 |edition= 8th.}}</ref> Some species, such as some [[snail]]s, practice [[Sequential hermaphroditism|sex change]]: adults start out male, then become female. In tropical [[clownfish]], the dominant individual in a group becomes female while the other ones are male, and bluehead wrasses (''[[Thalassoma bifasciatum]]'') are the reverse. 

[[File:ClownFishCycle.jpg|thumb|Life cycle of clownfish]]

Clownfish live in colonies of several small undifferentiated fish and two large fish (male and female). The male and female are the only sexually mature fish to reproduce. Clownfish are protandrous hermaphrodites, which means after they mature into males, they eventually can transform into females. They develop undifferentiated until they are needed to fill a certain role in their environment, i.e., if they receive the social and environmental cues to do so. <ref>Casas, L., Saborido-Rey, F., Ryu, T., Michell, C., Ravasi, T., & Irigoien, X. (2016). Sex Change in Clownfish: Molecular Insights from Transcriptome Analysis. Scientific Reports, 6(1). https://doi.org/10.1038/srep35461</ref>

Some species, however, have no sex-determination system. Hermaphrodite species include the common earthworm and certain species of snails. A few species of fish, reptiles, and insects reproduce by [[parthenogenesis]] and are female altogether. There are some reptiles, such as the [[boa constrictor]] and [[Komodo dragon]] that can reproduce both sexually and asexually, depending on whether a mate is available.<ref name="Watts-2006">{{cite journal | vauthors = Watts PC, Buley KR, Sanderson S, Boardman W, Ciofi C, Gibson R | title = Parthenogenesis in Komodo dragons | journal = Nature | volume = 444 | issue = 7122 | pages = 1021–1022 | date = December 2006 | pmid = 17183308 | doi = 10.1038/4441021a | name-list-style = amp | s2cid = 4311088 | bibcode = 2006Natur.444.1021W }}</ref>