Guide to Identification of
Fresh Water Microorganisms

Arthropods - Segmented, exoskeletons

 Name

Picture

Characteristic

Taxonomy

Ostracods
<2mm

1. bean-like shell
2. filter feeders

3. bivalve carapace

Class Crustacea
Order  Ostracoda

i.e. Cypris sp.

Copepods
.5-3mm

1. long antennae
2. tiny eyespot

3. holoplankton

Class Crustacea
Order Copepoda

Water fleas
.3-10mm

1. antennae
2. large compound eye
3. holoplankton

Class Crustacea
Order Cladocera

i.e. Daphnia sp

Isopods
5-20mm

1. flattened
2. 7 pairs legs

3. scavengers

Class Crustacea
Order Isopoda

Amphipods
5-25mm

1. curved
2. compressed body
3. humped back

4. scavengers

Class Crustacea
Order Amphipoda

Water mites
.5-5mm

1. 8 legs
2. round body
3. larvae (parasitic)
4. nymph looks like adult

Class Arachnida
Order Acarina

Alderfly nymph
5-25mm

1. one tail
2. long filaments along the abdomen

3. meroplankton

Class Insecta
Order Megaloptera

Family Sialidae

Caddisfly larva
3-40mm

1. cylindrical case for protection
2. distinct case but different materials

Class Insecta
Order Trichoptera

Stonefly nymph
<15 mm

1. two jointed tails (cerci)
2. carnivorous

3. indicates clean water

Class Insecta
Order Plecoptera

Mayfly nymph
<15mm

1. three jointed tails
2. leaf-like gills on sides

Class Insecta
Order Ephemeroptera

Damselfly
Nymph
<15mm

1. three leaf like tail appendages (gills)
2. extendable jaws

Class Insecta
Order Odonata

Zygoptera

Dragonfly nymph
<15mm

1. robust
2. no tail appendages

3. extendable jaws

Class Insecta
Order Odonata
Anisoptera

Water boatman nymph.and adult
10-15mm

1. no jaws
2. tube-like beak
3. nymphs donít have wings

Class Insecta
Order Hemiptera

Family Corixidae

Water beetle
<45mm


adult


nymph
1. strong jaws
2. tough shield

3. fierce predator

Class Insecta
Order Coleoptera

Family Elmidae

1. strong jaws
2. long segmented body

3. short legs

Mosquito larva
1-20 mm

1. long slender body
2. moves in undulating s curves

Class Insecta
Order Diptera

Drawings redrawn from http://www.microscopy-uk.org.uk/pond/index.html

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