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Subphylum Crustacea

(Cladocerans [water fleas], shrimps, copepods, amphipods [scuds], sow bugs, crayfish, fish lice)

Soil & Water Conservation Society of Metro Halifax (SWCSMH)

Family: Hyalellidae; View: lateral

Updated: October 09, 2013      Freshwater Benthic Ecology and Aquatic Entomology Homepage


Linnean system of hierarchical classification (Williams & Feltmate, 1992):

Classification of Crustacea and estimates of their numbers in North American freshwaters (Thorp & Covich, 1991)

TaxaWorldwide percentage found in freshwatersApproximate number of species in the US and Canada
Subphylum Crustacea<10%ca. 1500
  Class Cephalocarida0%0
  Class Branchiopoda
        (8 orders; includes cladocerans)
  Class Remipedia0%0
  Class Maxillopoda
    Subclass Branchiura
    Subclass Copepoda<15%>200
  Class Ostracoda>50%420
  Class Malacostracaca. 10% 
      Superorder Pancarida
        (Order  Thermosbaenacea)
ca. 50%1
      Superorder Peracarida
        (Orders Mysidacea,
              Amphipoda and Isopoda)
      Superorder Eucarida
        (Order Decapoda)

Diagnostic features of Crustacea (Mackie, 1998)


Indicator value (Thorp & Covich, 1991)

Nearly 4000 species of crustaceans inhabit freshwaters around the world, occupying a great diversity of habitats and feeding niches. Within pelagic and littoral zones, water fleas and copepods are the principal macrozooplankton, and benthic littoral areas shelter vast numbers of seed shrimps, scuds, and other crustaceans. An omnivorous feeding habit is typical of crustaceans, although there are many strict herbivores, carnivores, and detritivores. Members of the subphylum Crustacea are characterized by a head with paired mandibular jaws, a pair of maxillae, and two pairs of antennae. Their appendages are often biramous.

Class Malacostraca

Representatives of four groups of malocostracean crustaceans can form major components of the benthic fauna of some fresh waters.

Order Amphipoda (Scuds or side swimmers)

Order Isopoda (Aquatic Sowbugs)

Order Mysidacea (Opossum Shrimps) (Mackie, 2001)

Order Decapoda (Shrimps, Crabs, etc.)

Family Cambaridae (Crayfish)
Most species live for approximately 2 years although certain species may live up to 6 or 7 years. (Kellogg, 1994)
Family Palaemonidae (Freshwater Shrimp)
Although infrequently encountered in riffle areas of streams, freshwater shrimp may be common in slow moving brackish or freshwater streams coastal or lowland areas. (Kellogg, 1994)

Class Branchiopoda, Order Cladocera (Water Fleas) (Mackie, 1998)

Holopedium gibberum is characteristic of acidifying lakes and waters low in calcium.

Class Ostracoda (Wetzel, 1983)

The ostracods are small, bivalved crustaceans usually less than 1 mm in size, which are widespread in nearly all aquatic habitats. Ostracod densities increase in more productive lakes (to >50,000/sq.metre).

Micrographs of some crustaceans:


Order: Ostracoda (seedshrimps)


Order: Branchiopoda (cladocerans [water fleas]); Family: Chydoridae; View: lateral


Class: Copepoda; Left: Order Cyclopoida; Right: Order: Calanoida

References and web URLs:

Freshwater Benthic Ecology and Aquatic Entomology Homepage                     Soil & Water Conservation Society of Metro Halifax (SWCSMH) Master Homepage

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