Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada

Family Asellidae - Common Waterslaters

Water Hoglouse, Asellus sp - Caecidotea 6022244 Lirceus - Lirceus water sowbug - Caecidotea communis - male Sow Bug? - Caecidotea Freshwater Isopods - Caecidotea Caecidotea sp.? - Caecidotea Caecidotea sp. - Caecidotea unknown - Lirceus
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Crustacea (Crustaceans)
Class Malacostraca (Malacostracans)
Superorder Peracarida (Marsupial Crustaceans)
Order Isopoda (Isopods)
Suborder Asellota (Asellotes)
Superfamily Aselloidea (Waterslaters)
Family Asellidae (Common Waterslaters)
Other Common Names
Hoglice (some Eurasian species)
Numbers
over 350 species globally; in our area about 126 described species and numerous (at least 25 known and countless unknown) undescribed species in 10 genera
Identification
Key to Asellid genera of North America:

1a. Eastern and Great Plains → 2
1b. Montane and Pacific → 5

2a. Head with large lateral plates, often with a large notch in the sides; pleopod 3 with an oblique suture; epigean. stygobitic and phreatobitic → Lirceus
2b. Head lacking large lateral plates; pleopod 3 usually with a transverse suture (oblique in some Lirceolus) → 3

3a. Pereopod 1 ambulatory, pereopods 2-3 strongly natatory and hairy; N FL stygobite → Remasellus parvus (monospecific genus)
3b. Pereopod 1 subchelate (at least in ♂’s), pereopods 2-3 ambulatory and not as hairy →

4a. ♂ pleopod 2 exopod lacking plumose setae or catch lobe, protopod overlapping with exopod; pereopod 1 propus without processes; pleopod 3 with transverse or oblique suture; uropods very short, under half as long as telson OR telson smaller than pereonite 7; TX+MO stygobites → Lirceolus (dubiously seperated from Caecidotea[/i])
4b. ♂ pleopod 2 exopod with or without plumose setae, with catch lobe, protopod not overlapping with exopod; pereopod 1 propus with or without processes; pleopod 3 with transverse suture; uropods usually longer, averaging around 0.5x-2x as long as telson (shorter in a few species), telson generally larger than pereonite 7; epigean, stygobitic or phreatobitic → Caecidotea (in part)

5a. Eyed epigean species, usually heavily pigmented → 6
5b. Eyeless, generally with little to no pigment → 7

6a. ♂️ pleopod 2 endopod with large basal spur; ♂️ pereopod 1 palm process without processes; Alaska and San Fransisco → Asellus
6b. ♂️ pleopod 2 endopod with a small basal process or lacking basal process; ♂️ pereopod 1 palm process with or without processes; widespread → Caecidotea

7a. Head with a small rostrum; ♂️ pleopod 2 endopod basal spur absent; WA, MT and Alberta → Salmasellus
7b. Head lacking rostrum; ♂️ pleopod 2 endopod basal spur present (small and inconspicuous in Bowmanasellus); Pacific coast states → 8

8a. Mandible with only a stub of a palp; ♂️ pleopod 1 protopod with only 1 linking hook; endemic to Malheur Cave in SW OR → Oregonasellus elliotti (monospecfic genus)
8b. Mandible with a 3-segmented palp; ♂️ pleopod 1 protopod with more than 1 linking hook, usually 2-3; not in Malheur Cave → 9

9a. ♂️ pleopod 2 endopod with odd bumpy globose structure (“lateral process”) posterior to tip, medial process forming a distal spine; Sequoia and Kings Canyon NP in CA → Bowmanasellus sequoiae (monospecific genus)
9b. ♂️ pleopod 2 endopod lacking odd bumpy globose structure posterior to tip, cannula forming a distal spine (when present); PNW to central-southern California → 11

10a. ♂️ pleopod 2 endopod basal spur mostly obscured dorsally, cannula alone at tip; hyporheic PNW → Columbasellus acheron (monospecific genus)
10b. ♂️ pleopod 2 endopod basal spur plainly visible doe sally, cannula backed by a very long broad round-tipped caudal process; general phrearobitic C CA → Calasellus
Range
Holarctic
Habitat
Surface water species are restricted to 3 genera in North America (Caecidotea, Lirceus and Asellus)
Subterranean members of Caecidotea and Lirceus are also known, along with 7 small narrow-ranged subterranean-only genera (Lirceolus, Bowmanasellus, Calasellus, Columbasellus, Oregonasellus, Remasellus and Salmasellus)
Remarks
Across most of the continent there are only 1-2 genera in a given location, although in southern and western regions a few other genera are also known.
Caecidotea: +80 species found across the continent from west-central BC to Nova Scotia to the Everglades, probably absent from the southwest
Lirceus: +15 species endemic to the eastern US (S Quebec to E OK to N FL)
Asellus: only 2 species are known from North America: Asellus alaskensis from far northeastern Alaska and Asellus hilgendorfii introduced to central California. More are known from Eurasia
Remasellus: one species (R. parvus) endemic to N FL
Lirceolus: about 5-7 species mostly found in Texas (one in MO depending if it's placed here or in Caecidotea, while another reaches Coahuila), may just be a grade of abberant species in Caecidotea
Salmasellus: 2 species in the northwest in WA, Alberta and MT
Columbasellus: one species known from along the Columbia River in WA, probably more widespread
Oregonasellus: one species endemic to Malheur Cave, OR
Calasellus: at least 3 species (1 undescribed) in central CA
Bowmanasellus: one species endemic to Sequoia National Park in CA