Isopods are paradoxical for being simultaneously extremely obscure and also extremely charismatic. Ask any random person off the street what an isopod is and they would likely not know, yet within a smaller subset of people isopods are very popular to the point of creating a large invertebrate keeping industry around them. However, outside a very niche group of scientists, the only isopods that most people know to exist are the terrestrial isopods (Oniscidea) and giant isopods (Bathynomus). This is only a small fragment of the full diversity of isopods, with a fascinating array of fantastic and sometimes outright bizarre forms lost in a maze of endless scientific articles. The goal of this guide is to bring this unknown diversity out of extreme obscurity and to allow more people to explore the rich and utterly bizarre isopod fauna of North America.

the four kinds of isopods: just a little guy, giant freak, he who has seen the deep, and little guy (murder)

The four basic kinds of isopods: just a little guy, giant freak, ȟ̷̿e̸̔̃ ̸͂̿w̶̃̈́h̵͛̎o̵̓̉ ̴̊́h̷͋̒a̷̓͗s̵̉͑ ̴͒̉s̷͊̍é̵͘ë̵́͂n̶̽̈́ ̶̊̕t̶͛̅h̶̛͐e̸̛̎ ̷͛̋d̷̋̓è̶̚è̶͘p̴̃̃, and just a little guy (murder). Not pictured: incomrehensible lung-eating eldritch entity (too confusing)


Taxonomy is the study of sorting earth’s biosphere into discrete categories (or boxes), with the general idea of closer-related organisms sharing lower boxes. The main goal of taxonomy is to achieve monophyletic groups, where a group contains a common ancestor and all of its descendants, in contrast to paraphyletic groups, where a common ancestor and only some of its descendants are included, or polyphyletic groups, where the grouped organisms are seemingly random with no shared common ancestor (unless you look really far back). Taxonomy rides on descriptions of organisms (i.e. a descriptive science), which are a list of traits that the organism has. Traits can be divided into plesiomorphies, which are traits ancestral to a group, and apomorphies, which are derived traits that occur in a group, with an apomorphy defining a group called a synapomorphy. What traits are considered plesiomorphies and apomorphies is based on the context it is being used. For example, a chitinous jointed exoskeleton is a plesiomorphy for isopods, but in the context of all arthropods it is an apomorphy. A good example of a synapomorphy in Isopoda is biphasic molting (the front and back halves molt at different times), as it an important defining characteristic of the order. Sometimes a synapomorphy of a group will become lost in a highly derived subgroup; the presence of only 1 pair of uropods can be considered a synapomorphy for Isopoda, but they have reverted back to pleopods in Anuropidae and completely lost in Paravireia.
Taxonomy is currently split into two major directions: classical Linnaean Taxonomy, which groups organisms in hierarchical sets of nesting boxes called taxa (sing. taxon), and more modern cladistics, which divides organisms into discrete sets of nesting groups called clades. Typically, a combination of the two systems is used, with clades being given a taxonomic name to facilitate the understanding of a group. In Isopods, the largest clade that contains all isopods is currently set at the order level, with major subordinate clades being placed at the suborder level.

[drawings of concepts]

Unfortunately, taxonomy is very far from being a perfect science, and isopods are a prime example of this. Many taxa within Isopoda are very poorly defined, with many classic taxa likely being paraphyletic or even polyphyletic. The Taxonomic Guide attempts to organize our current knowledge of the relationships between different groups of isopods avaliable in current literature, but it is very likely that this organization will change dramatically in the future.


The order Isopoda is currently arranged into 12 suborders. They range in size from the monospecific Phoratopidea (only known from 2 specimens of 1 species off the coast of Australia) to Oniscidea, which contains almost a fourth of the total global Isopod diversity. Most of the suborders are generally easily recognizable from each other, with charismatic gestalts that allow for them to be instantly recognizable from each other in most cases, and even where differentiation is more difficult (i. e. Asellota vs Microcerberidea), specific characters can still facilitate identification. A short summary of each are provided below:

In addition, the suborder Flabellifera was recognized until fairly recently, when it was divided up into multiple suborders. The majority of species of Flabellifera went to the new suborders Sphaeromatidea and Cymothoida, while small fragments also going to Phoratopidea and Limnoriidea. The loose grouping is still useful on a gestalt ground to help narrow down to a currently accepted suborder, with former flabelliferans being recognized by the presence of a tailfan created from laterally articulating uropods and a wide telson.



Brandt, A., & Poore, G. C. (2003). Higher classification of the flabelliferan and related Isopoda based on a reappraisal of relationships. Invertebrate Systematics, 17(6):893-923.

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Published: Apr 1, 2023