Parasite: a eukaryotic organism that lives on or in a host, benefitting at its expense
Click the image below to be taken to an interactive phylogenetic tree, and click the number corresponding to the parasite species to be taken to its page:
*omitted: Myrmeconema neotropicum (phylum Nematoda) and Chondronema passali (also phylum Nematoda), which have not yet been added to the NCBI taxonomy database
Parasites can have direct (monoxenous) or indirect (heteroxenous) life cycles. Direct life cycles involve parasites that infect a single, definitive host species, and these can take parasitoid, castrator, or directly transmitted parasitic strategies. In indirect life cycles, parasites can have multiple hosts (for example, one or more intermediate hosts followed by the definitive host in/on which sexual reproduction takes place), and strategies include trophic or vector transmission. Additionally, a paratenic host may be involved in an indirect life cycle in which the parasite only uses the paratenic host for transport, not life stage completion. Micropredators feed on multiple hosts without killing them.
Cymothoa exigua (fish are currently this species' only known/studied host, though the life cycle is understudied)
Naegleria fowleri (one host, facultative parasite)
Perkinsus marinus (one host, facultative parasite)
Phoradendron leucarpum (hemiparasitic plant)
An example of a direct life cycle.
http://www.aquaticparasites.org/background.html
Direct life cycles may involve free-living stages or direct transmission of infectious stages through contact between hosts.
https://link.springer.com/chapter/10.1007/978-3-319-99194-8_9
Two-Host
Dracunculus medinensis (2-host, plus fish as potential paratenic hosts)
Three-Host
Dirofilaria immitis (2-host)
Leishmania tropica (2-host)
Loa loa (2-host)
Above: a trophically transmitted parasite's life cycle.
https://www.researchgate.net/figure/Indirect-life-cycle-where-the-fish-is-an-intermediate-host-The-nematode-eggs-larvae-a_fig3_251325739
Above: A vector-transmitted life cycle.
https://www.sciencedirect.com/science/article/pii/B9780128140437000042
Petromyzon marinus (ectoparasite that typically feeds on one host before detaching to breed elsewhere)
Nuytsia floribunda (hemiparasitic plant that parasitizes many hosts simultaneously)
Image Sources
Page Header
https://www.news-medical.net/news/20200519/Do-parasites-protect-against-SARS-CoV-2.aspx
https://www.sciencenews.org/article/malaria-parasites-may-have-their-own-circadian-rhythms
Plantae https://commons.wikimedia.org/wiki/File:Rafflesia_arnoldii_Bengkulu_02.jpg
Animalia https://www.acsh.org/news/2016/08/04/parasitism-evolved-at-least-223-times-among-animals
References
Poulin R. (2011). The many roads to parasitism: a tale of convergence. Advances in parasitology, 74, 1–40. https://doi.org/10.1016/B978-0-12-385897-9.00001-X