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Genus Caecidotea

Water louse - Caecidotea Asellus or Caecidotea - Caecidotea - male - female water sowbug - Caecidotea communis - male water sowbug - Caecidotea communis - male Asellus? - Caecidotea Isopod? - Caecidotea Freshwater Isopods - Caecidotea Lirceus - Caecidotea
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)
Genus Caecidotea
Other Common Names
American Waterslaters
Explanation of Names
Caecidotea Packard, 1871
The genus has a contorted history behind it. Originally erected to house the blind isopods in North America (caecus = blind in Latin), it was eventually lumped into Asellus and the split off to hold all members of Asellus native to North America (asides from A. alaskensis)(1)
Numbers
about 100 species globally, most (+80) are in the US and adjacent Canada
Size
Most species are generally around 5-15mm, the largest species (C. jordani) can reach to 30mm, while some very small species never reach more than 4mm
Identification
Species in Caecidotea are usually defined by features on the endopod of the male second pleopod, but other features can be used to narrow down an individual to species groups or even individual species. Getting shots of these specific features should help:
-a dorsal shot of the whole body to show pigmentation and proportions of certain areas
-a good shot of the claws (pereopod 1) from the side to see if there are any teeth on the "palm" and how they're arrangd
-a good shot of the underside of the telson to show the small pleopods near the base, this can help with sexing the individual since the pleopods differ between males and females along with species identification
Range
Endemic to North America (including Mexico and Guatemala), the range is split into 3 parts:
-a western range from BC to central California which has 2 closely-related species (occidentalis and tomalensis)
-a southern range from central Mexico to Guatemala, which has about 10-20 species
-an eastern range from Oklahoma and Texas east to Nova Scotia and the Everglades, which contains the bulk of the genus
Two eastern species (communis and racovitzai) are also widely introduced west of their normal range and in Europe, while there are apparently reports of one of the western species (occidentalis) in Utah
Habitat
Surface waters, groundwater or caves depending on the species. Surface species can be found by sifting through aquatic vegetation and leaf debris
Remarks
This massive genus has a good number of undescribed species in our area
Almost all of the species in Caecidotea used to be placed in Asellus until the 1970s, many resources still incorrectly place American asellids in this genus.(1) Currently, the only members of Asellus in North America are Asellus alaskensis in far northwestern Alaska (no overlap with Caecidotea) and the introduced Asellus hilgendorfii in the San Joaquin delta in California. These can be told from Caecidotea by the massive basal spur on the endopod of the male's pleopod 2.
See Also
Lirceus has large lateral plates on the sides of the head and usually has much wider bodies
Lirceolus is dubiously split from Caecidotea but all species within the overlap zone between the two genera in central Texas can be told from Caecidotea by their much smaller size.
In the west, almost all pigmented surface species are in Caecidotea, while all known pigment-free subterranean species are in a handful of small endemic genera. The only other pigmented surface species in the area Caecidotea is found in the west is Asellus hilgendorfii in central California, which has a large "spur" projecting from the inner bottom corner of the second pleopod's endopod. The head pattern may also be different between that species and the about 4 species of Caecidotea known from California, and the lack of teeth on the claws can also differentiate A. hilgendorfii from 2 of those Caecidotea species (communis and racovitzai)