# Hydrichthys

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***Hydrichthys*** is a [genus](/source/Genus) of colonial marine [hydrozoans](/source/Hydrozoa) formerly placed in the [family](/source/Family_(taxonomy)) Hydrichthyidae but is now included in the family [Pandeidae](/source/Pandeidae).[1] The [polyps](/source/Polyp_(zoology)) of members of this genus are [parasitic](/source/Parasitism). The polyp attaches itself to a fish, and in one species exhibits [hyperparasitism](/source/Hyperparasite) by attaching itself to a [copepod](/source/Copepod), itself the parasite of a fish.

## Parasitism

The life history of hydrozoans typically has a larval, [polyp](/source/Polyp_(zoology)) stage and a bell-shaped [medusa](/source/Medusa_(biology)) stage. In *Hydrichthys*, the polyp has no tentacles but develops a root-like stolon which it thrusts through the skin of its host, usually a fish, to suck the blood and body fluids. During the medusa stage, *Hydrichthys* lives independently in the ocean. In one species, *[Hydrichthys sarcotretis](/source/Hydrichthys_sarcotretis)*, parasitism is taken a stage further when the hydrozoan attaches itself to the [copepod](/source/Copepod) *[Cardiodectes medusaeus](/source/Cardiodectes_medusaeus)*. This is itself an ectoparasite of [lanternfish](/source/Lanternfish) in the family [Myctophidae](/source/Myctophidae). The copepod attaches itself to the [bulbus arteriosus](/source/Bulbus_arteriosus) of the fish. Such a parasitic chain is known as [hyperparasitism](/source/Hyperparasite).[2] The actions of the copepod castrate its fish host. Both male and female fish do not reproduce and seem to grow faster when attacked by the copepod and it seems to have a negligible energy demand from them.[3] The hydrozoan parasite castrates the copepod, a process called hypercastration.[2]

## Species

The World Register of Marine Species recognises the following species:[1]

- *[Hydrichthys boycei](/source/Hydrichthys_boycei)* Warren, 1916
- *[Hydrichthys cyclothonis](/source/Hydrichthys_cyclothonis)* Damas, 1934
- *[Hydrichthys mirus](/source/Hydrichthys_mirus)* Fewkes, 1887
- *[Hydrichthys pacificus](/source/Hydrichthys_pacificus)* Miyashita, 1941
- *[Hydrichthys pietschi](/source/Hydrichthys_pietschi)* Martin, 1975
- *[Hydrichthys sarcotretis](/source/Hydrichthys_sarcotretis)* (Jungersen, 1913)

## References

1. [*Hydrichthys* - Fewkes, 1887](http://www.marinespecies.org/aphia.php?p=taxdetails&id=117123) World Register of Marine Species. Retrieved 2011-10-10.

1. Bush, Albert O. (2001). [*Parasitism: the diversity and ecology of animal parasites*](https://books.google.com/books?id=Q6Kl0FbvStoC&dq=Peachia+quinquecapitata&pg=PA287). p. 285. ISBN 978-0-521-66447-9.

1. Moser, Mike & Taylor, Sam (1978). ["Effects of the copepod *Cardiodectes medusaeus* on the laternfish *Stenobrachius leucopsarus* with notes on hypercastration by the hydroid *Hydrichthys sp.*"](http://www.nrcresearchpress.com/doi/abs/10.1139/z78-321). *Canadian Journal of Zoology*. **56** (11): 2372–6. [doi:10.1139/z78-321](https://doi.org/10.1139/z78-321)

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Adapted from the Wikipedia article [Hydrichthys](https://en.wikipedia.org/wiki/Hydrichthys) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Hydrichthys?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.