Ecologist's Guide to Parasites

For BIO 361: Biodiversity of Parasites

An introduction to parasite diversity through a focus on thirty species

Parasite: a eukaryotic organism that lives on or in a host, benefitting at its expense

Phylogenetic Tree

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

Click links below to be introduced to a number of parasites in the following kingdoms:


Parasites by Life Cycle

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.

Below, parasites are organized in terms of life cycles and parasitic strategies


Parasitoid (kills the host)

  1. Massospora cicadina

Castrators (render host incapable of reproduction)

  1. Sacculina carcini

  2. Massospora cicadina

Directly Transmitted Parasites

  1. Trichomonas gallinae

  2. Rafflesia arnoldii

  3. Myrmeconema neotropicum

  4. Cymothoa exigua (fish are currently this species' only known/studied host, though the life cycle is understudied)

  5. Pseudodiplorchis americanus

  6. Mermis nigrescens

  7. Ophiocordyceps unilateralis

  8. Cryphonectria parasitica

  9. Pseudogymnoascus destructans

  10. Chondronema passali

  11. Pinnotheres pisum

  12. Hemileia vastatrix

Divergent Single-Host Strategies

  1. Naegleria fowleri (one host, facultative parasite)

  2. Perkinsus marinus (one host, facultative parasite)

  3. Phoradendron leucarpum (hemiparasitic plant)

An example of a direct life cycle.

Direct life cycles may involve free-living stages or direct transmission of infectious stages through contact between hosts.


Trophically Transmitted


  1. Toxoplasma gondii

  2. Leucochloridium paradoxum

  3. Spinochordodes tellinii

  4. Myxobolus cerebralis

  5. Dracunculus medinensis (2-host, plus fish as potential paratenic hosts)


  1. Dirofilaria immitis (2-host)

  2. Leishmania tropica (2-host)

  3. Loa loa (2-host)

Above: a trophically transmitted parasite's life cycle.

Above: A vector-transmitted life cycle.


  1. Petromyzon marinus (ectoparasite that typically feeds on one host before detaching to breed elsewhere)


  1. Neottia nidus-avis

  2. Nuytsia floribunda (hemiparasitic plant that parasitizes many hosts simultaneously)