TAXONOMY OF ISOPODA
FIRST: A primer on Taxonomy
Taxonomy is the study of organizing organisms into discrete units called taxa. The best way to understand the science of taxonomy is to imagine a series of nesting boxes similar to a matryoshka doll. An object placed in one of the smaller boxes is simultaneously in the smaller box and the larger box that holds the smaller box. Similarly, in taxonomy, organisms are placed into nesting taxa, so a member of the species Armadillidium vulgare is both in the genus Armadillidium and Oniscidea (which contains Armadillidium in it). Traditionally, each “level” of taxa were given names in the classic phylum-class-order-family-genus-species order, however in recent times this has been loosened, with more emphasis being placed on clades or a group united by a set of clades. For the sake of clarity, the traditional taxa level names are used to help define where a specific taxa is relative to others. A full list of the terms for taxa levels used in the guide from largest to smallest is displayed below:
Order
Suborder
Infraorder
Superfamily
Family
Subfamily
Tribe
Genus
Complex
Species
Subspecies
Common names, which can often function as a more accessible set of names that scientific names, are more or less nonexistent in Isopods. In the groups without common names, common names are coined to facilitate knowlegnjtbgfnjro
ISOPOD TAXONOMY
Isopods consist of the members of the creatively named order Isopoda, which in turn is part of the larger superorder Peracarida, also called the marsupial shrimps (see below). Isopoda is split into 12 suborders, each of which usually form fairly monotone units that are distinct from other suborders other (outside of Asellota and Microcerberidea, which are very similar, and Cymothoida, which is very diverse and likely not a natural group). Out of the 13 suborders, 8 occur in our area, with the other 5 either being small in diversity or geographically restricted. A quick overview of each suborder in our area is provided below:
Asellota (Asellotes): a huge group of somewhat relictual isopods and the earliest off-branching group in our area. There are two major centers of diversity of the suborder: in freshwater environments across North America and Eurasia (Waterslaters) and in abyssal environments worldwide (Deepsea Witchers), with a moderate diversity also occurring in much shallower marine waters.
Microcerberidea (Cerberuses and Pillslaters): a very small suborder that closely resembles (and probably is closely related to) Asellota, but is distinguished through differences in the genitalia (outlined in more detail in the morphology section). One family (Microcerberidae, Cerberuses) contains a small extremely ancient radiation of sand-dwelling organisms in both fresh and marine waters, while the second order (Atlantasellidae: Pillslaters) contains only 2 species endemic to the caves on Hispaniola and in Bermuda
Oniscidea (Woodlice and allies): the largest isopod suborder and the second largest group of terrestrial crustaceans outside of insects, numerous adaptations to terrestrial life allow about 4000 species of woodlice to thrive on land across the planet. Curiously, the diversity of native woodlice drops significantly north of the US-MEX border despite being very diverse in similar latitudes on other continents, although this gap is partially filled by numerous species introduced from other regions (mainly Europe) since the start of European colonization in the Americas.
Valvifera (Valvetails): a moderately large suborder of unique-looking isopods,
Sphaeromatidea (Seapills and Trisobites)
Limnoriidea (Gribbles and allies)
Cymothoida (Wormpods and Fisheaters
Epicaridea (Eldritch Isopods)
Four additional orders occur entirely outside of the area covered by the AIMG, for interest, these orders are listed below:
Phreatoicidea (Grigslaters): an ancient group of isopods with an odd, almost amphipod-like body shape. Currently, grigslaters are restricted to freshwater and semiterrestrial environments in Australia, New Zealand, South Africa and India, but fossils reveal a much more diverse globe-spanning Phreatoicidea going as far back as the Carboniferous, including at least a few marine species.
Calabozoidea (Slaterlice): a very small group of isopods that are probably related to Asellota+Microcerberidea, Oniscidea or both. The entire group is endemic to groundwater habitats in tropical South America.
Tainisopidea (Water-Earwigs): a strange group of subterranean isopods endemic to western Australia that appears to be basal to all isopods outside of Phreatoicidea, Asellota+Microcerberidea, Calabozoidea and Oniscidea. Many members of this suborder vaguely resemble earwigs, hence the name coined for them.
Phoratopidea (Oarsman): an enigmatic suborder containing a single species that has only been collected twice off southern Australia. An odd array of features suggests a basal relationship to either Cymothoidea,
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