Epicaridea Latreille, 1825

Main Page | Isopoda > Epicaridea

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 the often incomprehensible shapes achieved by adult ♀♀ in many taxa.
Taxonomic History: Epicaridea Latreille, 1825
Description: Body fairly broad to somewhat elongate depending on life stage, most species (and all larval forms) dorsoventrally compressed (highly derived adult ♀♀ often amorphous); post-manca juveniles stages highly modified with dramatically different ecologies and morphologies over a 4-step maturation, adult sexual dimorphism extreme, ♂♂ highly simplified isopodiform (i.e. looks like a very simplified version of a normal isopod), ♀♀ immensely to incomprehensibly contorted. Antenna 1 frequently reduced in segments but still of considerable size compared to antenna 1, set dorsally to medially; peduncle segment 3 without scale. Antenna 2 peduncle segment 3 without scale. Mandible massively simplified to a stylet-like appendage, lacking all normal structures. Maxilla 1 uniramous in epicaridium larvae, absent in microniscus and adult stages (apparently only 1 maxilla remaining in cryptoniscus larvae). Maxilla 2 uniramous in the epicaridium larvae, absent in microniscus and adults and (apparently only 1 maxilla remaining in cryptoniscus larvae). Maxilliped massively reduced to a biarticulated structure in epicaridium larvae (often reduced), endite frequently with distal setae. Pereonite 1 articulated to head in at least larval stages (frequently at least delineated by a suture in adults). Pereonite 7 in cryptoniscus larvae subsimilar to other pereonites (epicaridium larvae represent manca stages and therefore have a reduced pereonite 7); dorsal coxal plate subsimilar to other plates. Pereopod 1 subchelate. Pereopods 2-7 coxae all modified into coxal plates (not visible on epicaridium larvae but well-defined in cryptoniscus larvae), plates apparently articulated with tergites and sternites[?] (at least well-defined by sutures if not). Pereopod 7 present in cryptoniscus larvae (epicaridium larvae represent manca stages and therefore lack pereopod 7). Penes medial, closer to ventral midpoint than to pereopod bases. Pleonites 1-5 all articulating in larval stages, at least delineated by sutures or fused in adult stages, combined length noticeably longer than telson. Pleonite 1 subequal in width to pleonite 2. Pleopods 1-5 epipods absent. Pleopod 1 sexual dimorphism not quite present, pleopods often lobe-like or absent in adults. Pleopod 2 sexual dimorphism not quite present, pleopods often lobe-like or absent in adults (appendix masculina appears to be absent). Pleopod 3 endopod ovate, tip blunt. Telson wider than deep; ventral surface flat, without ventrolateral shelf, uropod notches absent. Uropod present only in epicaridium and cryptoniscus stages, ventrolateral (present and marginal in adult stages of some Bopyridae), otherwise absent; rami apparently subterete; exopods plane with endopods.
Type taxon: Bopyroidea Rafinesque, 1815
Notes: With a complex cycle that includes 2 planktonic dispersal stages, and the extreme simplification of the adult bodies often to the point of incomprehensibility, members of Epicaridea represent some of the more extreme boundaries to the typical isopod bauplan. All species in this suborder are parasitic on other crustaceans, with a majority being exoparasites (including and especially the branchial chamber of decapods) while others are endoparasitic into the viscera. Epicarideans show some fascinating convergent evolution with other crustacean-parasitic crustaceans, especially the barnacle infraclass Rhizocephala, with some species of epicarideans even being first described as a rhizocephalans (or vice versa)!
The life cycle of epicarideans is one of the more unique traits of the suborder. Traditionally, the life cycle is split into 4 stages:
- Epicaridium: free-living and non-feeding. The body is usually fairly short and lacks pereopod 7, indicating that this stage is a highly derived manca stage. Usually swims around with the legs locked to the body, but occasionally curls the body and extends the often elongated pereopod 6 pair out as if sensing for an intermediate host.
-Microniscus: ectoparasitic on copepods. Functionally acts as a feeding pupa stage, with the body becoming extremely soft and rapidly growing and changing throughout this stage. Originally thought to be a seperate taxon from the other stages, this stage is poorly known due to not occuring with the ultimate hosts like the other three stages.
-Cryptoniscus: free-living and non-feeding (until a host is found). Arguably the most "normal"-appearing stage, this stage is somewhat analogous to the juvenile and ♂ stages of Cymothoidae. The body is well-defined, with distinct features and a hard cuticle. Once a host is found, the larvae either becomes a ♀ (if the host is unoccupied) or a ♂ (if the host is occupied), usually with a transitional juvenile stage between this stage and the adult.
-Adult: ecto- or endoparasitic on the ultimate hosts. The well-defined features of the cryptoniscus degrade into a fleshy mass, with the final appearance ranging from having at least some visual affinity to other isopods (Bopyroidea) to loosing any sort of external indication that the creature at hand is a crustacean (many Cryptoniscoidea). In most Cryptoniscoidea, the ♂ never transition to any other state, remaining identical to the cryptoniscus.

Subordinate taxa: Bopyroidea, Cryptoniscoidea

Key to superfamilies (modified from Boyko & Williams, 2015)
1 a. Adult ♂♂ differentiated from cryptoniscus larvae, appearing fleshy and simplified; cryptoniscus antenna 2 with 3-4(-5) flagellomeres; adult ♀♀ generally attaching externally either on the external surface or on the branchial chambers on Decapods (creating an increasingly elongate pocket into the body to become endoparasitic in Entoniscidae) --> Bopyroidea
b. Adult ♂♂ neotenic, identical with the cryptoniscus larvae (differentiated in some groups); cryptoniscus antenna 2 with 5 flagellomeres; adult ♀♀ commonly occuring in the marsupia of other Peracaridans but also occuring externally or internally and occuring on other groups of crustaceans --> Cryptoniscoidea

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

Sources

Anderson, G. & Dale, W. E. (1981). Probopyrus pandalicola (Packard) (Isopoda, Epicaridea): morphology and development of larvae in culture. Crustaceana, 41:143-161.

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.

Boyko, C. B., Williams, J. D., & Sancetta, G. (2024). The epicaridium larvae of Paragigantione species (Isopoda: Epicaridea: Bopyridae) have external yolk sacs: transfer of the genus to Pleurocryptellinae, description of two new species in the genus and a new species of hyperparasite (Isopoda: Epicaridea: Cabiropidae). Systematic Parasitology, 101(6):70.

Hosie, A. M. (2008). Four new species and a new record of Cryptoniscoidea (Crustacea: Isopoda: Hemioniscidae and Crinoniscidae) parasitising stalked barnacles from New Zealand. Zootaxa, 1795(1):1-28.

Huys, R., Savchenko, A. S., & Kosobokova, K. N. (2023). Discovery of a new species and host record of Holophryxus Richardson, 1905 (Isopoda: Dajidae) from the central Arctic: a model of enhanced descriptive standards for epicaridean isopods. Zoological Journal of the Linnean Society, 20:1-58.

Oanh, L. T. K., & Boyko, C. B. (2020). Cancrion khanhensis sp. nov. (Crustacea: Isopoda: Entoniscidae) infesting Monomia haanii (Stimpson, 1858) (Crustacea: Brachyura:  Portunidae) from Nha Trang Bay, Khanh Hoa, Vietnam, with remarks on larval stages of Entoniscids and description of a new family, genus and two new species of hyperparasites infesting entoniscids. Zootaxa, 4894(3):366-386.

Schädel, M., Perrichot, V. & Haug, J. T. (2019). Exceptionally preserved cryptoniscium larvae - morphological details of rare isopod crustaceans from French Cretaceous Vendean amber. Palaeontologia Electronica, 22.3.71:1-46. 

Shiraki, S., & Kakui, K. (2024). Isopods on isopods: integrative taxonomy of Cabiropidae (Isopoda: Epicaridea: Cryptoniscoidea) parasitic on anthuroid isopods, with descriptions of a new genus and three new species from Japan. Invertebrate Systematics, 38(8).

Schultz, G. A. (1977). Bathypelagic isopod Crustacea from the Antarctic and southern seas. Biology of the Antarctic seas V, 23:69-128.

Williams, J. D., Boyko, C. B., & Stewart, E. C. (2024). Establishment of a new subfamily for the parasitic isopod genus Pleurocryptella (Isopoda: Bopyridae), including recognition of epicaridium larval yolk sacs and description of a new genus and species of hyperparasite. Journal of Crustacean Biology, 44(2):ruae034.

Williams, J. D., Boyko, C. B., Tepolt, C. K., & Blakeslee, A. M. (2023). Cryptic diversity in endoparasitic isopods (Bopyroidea: Entoniscidae) from mud crabs (Panopeidae) along the Atlantic coast of North America, with the description of a new genus and new species as revealed by molecular and larval characters: the long and the short of it. Journal of Crustacean Biology, 43(1):1-20.

Published: Jan 1, 2023
Updated: Aug 5, 2025