Epicaridea Latreille, 1825

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Suggested Common Name: Eldritch Isopods
Number of subordinate taxa: 862 species in 2 superfamilies globally, 144 species in both superfamilies in our area.
Etymology: epi- = on [multilingal] + Caridea [True Shrimps], refering to this infraorder's parasitism on shrimps (and other crustaceans). Common name refers to how utterly bizarre this group is to the point of near indescribability, much like the Lovecraftian monsters that many resemble.
Taxonomic History: Epicaridea Latreille, 1825
Description: Body highly modified with 4 unique stages: a free-living epicaridium stage, a copepod-parasitic microniscus stage, a free-living cryptoniscus stage and an adult stage in an ultimate host. Epicaridium freeliving. Microniscus parasitic on calanoid copepods. Cryptoniscus freeliving. Adult ♂ with typical isopod morphology, symmetrical, although generally simpified, living on surface of ♀; ♀ highly contorted, asymmetrical, ranging from appearing like a flattened somewhat contorted isopod to an unrecognizable blob entirely consisting of ovaries with an anchoring mechanism, parasitic on various crustaceans but not copepods. A more complete diagnosis of the group is coming out soon.
Type taxon: Bopyroidea Rafinesque, 1815
Notes: No words in the english language can describe how utterly bizarre the Epicarideans are. The adults of many species are reduced to what are effectively ovaries with an anchoring system and some others (especially Entoniscids) delve straight into incomprehensibility. All members are parasites of crustaceans, with most well-studied groups (like Bopyrids) being found on Decapods, although the true extent of this group is very poorly known in part to their cryptic lifestyles. Some of the more reduced species strongly resemble other groups that had similar lines of evolution, especially Rhizocephalans (parasitic barnacles), and in many cases a species described as a member of one group has been discovered to be a member of another group.
Due to problems in obtaining some literature, the superfamilies of Epicaridea are currently not prepared in time for the Taxonomic Guide's release. The superfamilies will be released alongside lower taxa accounts when they are complete. For the time being, a provisional family key based on adult ♀'s has been included below. This key will be updated as more information on morphological characteristics (especially for Cryptoniscidae and Cabiropidae) becomes avaliable.
Recent genetic studies have indicated that this clade, often regarded as an infraorder in recent times, should be returned to the subordinal level (An et. al. 2022). This change is reflected in the guide for the time being, although it may be reversed upon new information being released.

Subordinate taxa: Bopyroidea, Cryptoniscoidea

Key to superfamilies (modified from Boyko & Williams, 2015)
1 a. Cryptoniscus antenna 2 with 5 flagellomeres; adult ♀ internal (not as below) or marsupial, if external then marsupia divided --> Cryptoniscoidea
b. Cryptoniscus antenna 2 with 4 flagellomeres; adult ♀ external or branchial, if internal then surrounded by a sack made of host blood cells --> Bopyroidea

Provisonal key to families known in the AIMG area based off of adult ♀s*
1 a. Body symmetrical; ovaries divided into 2 chambers; external or internal --> Dajidae
b. Body asymmetrical; ovaries not divided --> 2

2 (1) a. Situated on the surface of host or inside the branchial chamber --> 3
b. Situated in the haemocoel or marsupia of the host --> 4

3 (2) a. Uropods with numerous long straps that resemble bristles; solely branchial --> Ionidae
b. Uropods lacking long straps, generally simple; branchial or abdominal --> Bopyridae

4 (2) a. Various appendages grossly extended into "wings", almost making the isopod look a biblical angel, but with basic structure (especially the pleon) still being visible; body encased in a sheath made from blood cells of hosts; on Decapods--> Entoniscidae
b. Not as above, body usually compact or occasionally with "ribbons" but then with no basic structure visible; on Decapods, Peracarideans, Cirripedes and other crustaceans --> 5

5 (4) a. Front half of body "normal", resembling average isopod, back half irregular; parasites in barnacles along the temperate Pacific Coast and Nova Scotia --> Hemioniscidae
b. Body asymmetrical or blobby; ecology otherwise --> 6

6 (5) a. Body bopyroid, with visible segments and appendages; occuring in the haemolymph of decapods --> Entophilidae
b. Body irregular-blobby, segments reduced or entirely absent; hosts various --> 7

7 (6) a. Hosting on Paranebalia --> Apocumoechus
b. Hosting on other crustaceans --> 8

8 (7) a. Generally hosting on isopods; body often "segmented" or laterally compressed (Cabirops-type morphology) --> Cabiropidae
b. Generally hosting on rhizocephalans or decapods; body generally not "segmented" or laterally compressed  --> Cryptoniscidae

*Thermaloniscus is only known from a cryptoniscus larvae found near a hydrothermal vent far off the Pacific coast of Central America


An, J., Yin, X., Chen, R., Boyko, C. B., & Liu, X. (2022). Integrative taxonomy of the subfamily Orbioninae Codreanu, 1967 (Crustacea: Isopoda) based on mitochondrial and nuclear data with evidence that supports Epicaridea Latreille, 1825 as a suborder. Molecular Phylogenetics and Evolution, 107681.

Boyko, C. B., & Williams, J. D. (2015). A new genus for Entophilus mirabiledictu Markham & Dworschak, 2005 (Crustacea: Isopoda: Cryptoniscoidea: Entophilidae) with remarks on morphological support for epicaridean superfamilies based on larval characters. Systematic parasitology, 92(1):13-21.

Published: Jan 1, 2023
Updated: Nov 1, 2023