Asellota Latreille, 1802

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Suggested Common Name: Asellotes
Number of subordinate taxa: about 2300 species in 4 superfamilies and 1 incertae sedis family worldwide, 487 species in all four superfamilies occurring in our area, making it the second most diverse superorder in our area (just short of Cymothoida's 489 species)
Etymology: after Asellus Geoffroy, 1762, see that account for details. Common name is an anglicized version of the scientific name
Taxonomic History: Asellota Latreille, 1802. Microcerberidea was formerly subsumed under this suborder, but was split out during the 80s-00s.
Description: (modified from Poore, 2002) Antenna 2 with or without scale. Pereopod 1 subchelate or ambulatory (chelate in Katianiridae). Pereopods 2-7 with coxae ring-like around the base of the legs. Spermathecal ducts complex, opening dorsally or ventrally. Pleon with 1-2(-3) free segments, generally greatly reduced and not reaching the margin (large and reaching the margin in Stenasellidae). ♂ pleopod 1 present, uniramous, forming cover over genitalia. ♀ pleopod 1 absent. ♂ pleopod 2 biramous or with exopod fused with protopod; exopod (or fused exopod-protopod) strong, assistive in copulation; endopod copulatory, geniculate. ♀ pleopod 2 present, either separate or joined into a flap. Pleopod 3 present, biramous, either operculiform or simple. Uropods set near the tip of telson. Anus exiting near the tip of the telson.
Type taxon: Aselloidea Latreille, 1802
Notes: This enormous suborder is the second largest in Isopoda, with only Oniscidea being more specious. A large chunk of Asellota's diversity comes from two major radiations: a fairly large radiation into freshwater environments mostly in the Holarctic (Aselloidea) and an enormous radiation into deepsea environments (Janiroidea). Microcerberidea is very close to Asellota and was formerly considered a consituent of Aselloidea.
The taxonomy of the superfamilies are still in flux and it is very likely that the consituents of the 3 marine superfamilies will get shuffled around in the future. The sole differentiating features betwen each superfamily, the shape and size of pleopods 1-3, seems to be fairly weak phylogenetically, with many families (especially in Janiroidea) seemingly being closer to members of the other marine superfamilies despite their pleopodal arrangement. Aselloidea is most likely monophyletic due to its unique ecology and presumed ancient age.

Subordinate taxa: Aselloidea, Gnathostenetroidioidea, Janiroidea, Stenetrioidea

Key to superfamilies
1 a. Pleopod 3 operculate, with shorter pleopod(s) visible in front of it; marine or freshwater → 2
b. Pleopod 3 not operculate, either pleopod 1 (♂️), pleopod 2 or a combination of the two acting as an operculum, the resulting operculum with no shorter pleopods in front of it; marine (some Janiroidea freshwater along the immediate coast) → 3

2 (1) a. ♂️ pleopod 1 protopods separated; ♂️ pleopod 2 exopods large, circular, often fringed with setae; ♀️ pleopod 2 separated; Nearctic freshwater south to Guatemala (sometimes swept to sea after storms) → Aselloidea
b. ♂️ pleopod 1 protopods fused; ♂️ pleopod 2 exopods small; ♀️ pleopod 2 fused; tropical-marine → Stenetrioidea

3 (1) a. ♂️ pleopod 1 broad, opercular, with protopod present, endites free; ♂️ pleopod 2 small and hidden behind pleopod 1; ♀️ pleopod 2 with protopod present; tropical shallow water and N Caribbean anchialine → Gnathostenetroidoidea
b. ♂️ pleopod 1 narrow, protopod fused to endites; ♂️ pleopod 2 large, forming operculum with pleopod 1; ♀️ pleopod 2 lacking protopod; widespread habitats from polar to tropical → Janiroidea

Sources

Kensley, B., & Schotte, M. (1989). Guide to the marine isopod crustaceans of the Caribbean. Smithsonian Institution Press.

Poore, G. C. (2002). Asellota. Zoological Catalogue of Australia, 19:32-34.

Published: Jan 1, 2023