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: Body form extreme diverse, generally ovate to elongate-ovate (rarely subrectangular) with a large shield-like telson; sexual dimorphism outside basic features present, mainly involving pleopods 1-2. Antenna 1 usually well developed (secondarily reduced in some taxa); scale absent. Antenna 2 scale present or absent. Mandible incisor present, usually multicuspidate; lacinia present, usually multicuspidate; spine row present, often prominent; molar present, usually truncate (sometimes conical to elongate); palp large, 3-segmented, often secondarily reduced to absent. Maxilla 1 briamous, rami well-developed. Maxilla 2 exopod biramous with 2 endites, endites subequal in size; endopod as long as or shorter than endopod endites. Maxilliped epipod present, usually ovate; basis body not dominating maxilliped structure; endite large, subquadrate, partially to completely fused to basis, usually narrower than basis; palp 5-segmented (often secondarily reduced). Pereopods 2-7 coxae free, ring-like, often with a dorsally-visible projection. Penes separate, conical and close to elongate and far. Pleon almost entirely fused with telson, extremely short and often not visible dorsally, with 0-2(-3) extremely short free segments, lateral margins usually not free or at least not as wide as telson. Pleopod 1 highly modified, sexually dimorphic; male pleopod uniramous, consisting of a basal protopod and a distal endite (=exopod) or fused into one piece; female pleopod absent. Pleopod 2 highly modified, sexually dimorphic; ♂ pleopod biramous, protopod subquadrate to semicircular, endopod small, ovate, highly muscular, “thrusting”, set distally on protopod, endopod highly modified, fused with appendix masculina, geniculate (often segmented at elbow), set distomedially on protopod; female pleopod uniramous, 1-2-segmented, sides separate or fused, small or operculate. Pleopod 3 endopod ovate, rounded. Telson huge, shield-shaped, shallowly domed ventrally. Uropod set distally on telson, often in a notch in the telson, biramous or secondarily reduced.
Type taxon: Aselloidea Latreille, 1802
Notes: Asellota is the second largest suborder in Isopoda (behind Oniscidea), with the vast majority of the radiation occurring in multiple huge deepsea radiations within the potentially paraphyletic Janiroidea. Another large radiation, although nowhere near the scale of Janiroidea, has occurred in Holarctic freshwater environments with the family Asellidae, which has numerous epigean species and an even higher number of subterranean species. In contrast, Asellotes are relatively poorly represented in shallow marine waters, possibly due to outcompetition by Scuticoxiferans.
The taxonomy of the superfamilies are still in flux and it is very likely that the constituents of the 3 marine superfamilies will get shuffled around in the future. Aselloidea is most likely monophyletic due to its unique ecology and presumed ancient age, but the other 3 suborders are probably paraphyletic or even polyphyletic among each other. Genetic and full morphological studies on the group are needed, although the rarity of many groups, especially many families of deepsea Janiroideans, will make such study difficult to achieve.

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


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.

Wilson, G. D. F. (1987). The road to the Janiroidea: Comparative morphology and evolution of the  asellote isopod crustaceans. Journal of Zoological Systematics and Evolutionary Research, 25(4), 257-280.

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