Editing Parasitism (section)

==== Parasitic castrators ====

{{main|Parasitic castration}}

[[File:Sacculina carcini.jpg|thumb|The parasitic castrator ''[[Sacculina carcini]]'' (highlighted) attached to [[Liocarcinus holsatus|its crab host]]]]

[[Parasitic castrator]]s partly or completely destroy their host's ability to reproduce, diverting the energy that would have gone into reproduction into host and parasite growth, sometimes causing gigantism in the host. The host's other systems remain intact, allowing it to survive and to sustain the parasite.<ref name=PoulinRandhawa2015/>{{sfn|Poulin|2007|p=111}} Parasitic crustaceans such as those in the specialised [[barnacle]] genus ''[[Sacculina]]'' specifically cause damage to the gonads of their many species<ref name="Elumalai Viswanathan Pravinkumar Raffi">{{cite journal |last1=Elumalai |first1=V. |last2=Viswanathan |first2=C. |last3=Pravinkumar |first3=M. |last4=Raffi |first4=S. M. |title=Infestation of parasitic barnacle Sacculina spp. in commercial marine crabs |journal=Journal of Parasitic Diseases |volume=38 |issue=3 |date=2013 |doi=10.1007/s12639-013-0247-z |pmid=25035598 |pages=337–339|pmc=4087306 }}</ref> of host [[crab]]s. In the case of ''Sacculina'', the testes of over two-thirds of their crab hosts degenerate sufficiently for these male crabs to develop female [[secondary sex characteristic]]s such as broader abdomens, smaller [[chela (organ)|claws]] and egg-grasping appendages. Various species of helminth castrate their hosts (such as insects and snails). This may happen directly, whether mechanically by feeding on their gonads, or by secreting a chemical that destroys reproductive cells; or indirectly, whether by secreting a hormone or by diverting nutrients. For example, the [[Trematoda|trematode]] ''[[Zoogonus lasius]]'', whose [[Trematode life cycle stages|sporocysts]] lack mouths, castrates the intertidal marine snail ''[[Tritia obsoleta]]<!--formerly Ilyanassa-->'' chemically, developing in its gonad and killing its reproductive cells.{{sfn|Poulin|2007|p=111}}<ref name=Cheng13>{{cite book |last=Cheng |first=Thomas C. |title=General Parasitology |url=https://books.google.com/books?id=d4GQlYzode8C&pg=PA13 |year=2012 |publisher=Elsevier Science |isbn=978-0-323-14010-2 |pages=13–15}}</ref>