1. The document provides information on identifying freshwater microorganisms including algae, protozoa, and other plankton through descriptions, pictures, and taxonomic classifications. 2. Key details are given for different types of algae such as green algae, desmids, diatoms, and filamentous green algae. 3. Freshwater protozoa described include flagellates, amoebas, heliozoans, and various ciliates. 4. Other freshwater plankton outlined consist of cyanobacteria, euglenoids, dinoflagellates, rotifers, hydra, flatworms, and more.

1. Guide to Identification of Fresh Water
Microorganisms
Microscopic autotrophic organisms (i.e. algae)
Name Picture Characteristic Taxonomy
Green algae Phylum
1. flagella
(with Chlorophyceae
2. small
flagella, i.e.
3. solitary
small) Chlamyolomonas
4. rapid movement
<.05 mm sp.
Green algae
1. spherical Phylum
(with
2. colonial Chlorophyceae
flagella)
3. with two flagella i.e. Volvox sp.
.5-2mm
1. spherical to
Green algae conical Phylum
(no flagella) 2. not attached to Chlorophyceae
<.5 mm surface i.e. Pediastrum sp.
3. no movement
Filamentous 1. non branching Phylum
green algae 2. chains of cells Gamophyceae
<.1 mm – with chloroplast i.e. Zygnema sp.
cms 3. no flagella Spirogyra sp.
1. green
2. no flagella
Phylum
3. mainly solitary,
Desmids Gamophyceae
some colonial
<.5 mm i.e. Desmidium sp
4. various shapes
Closterium sp.
5. two semi-cell,
mirror image
1. one cell
2. slow gliding
motion Phylum
Diatoms 3. solitary or Bacillariophyceae
<.5 mm colonial i.e. Pennales,
4. cell wall Centric
(frustules) made
of silica
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2. Protozoa – heterotrophic only
Name Picture Characteristic Taxonomy
1. one or more
flagella
Flagellates 2. colonial or free Zoomastigophora
<.5mm living i.e choanoflagellates
3. with or without
lorica
1. pseudopodia Sacrodina
Amoeba
2. slow movement Order Amoebina
.02 –5 mm
3. engulfs food i.e. Amoeba proteus
1. amoeba with a
Shelled shell, usually Sacrodina
Amoeba sand grains Order Testacea
.1-.4 mm 2. pseudopodia i.e Arcella sp.
3. slow movement
1. spherical
Heliozoans 2. radiating hair Sacrodina
.01-1 mm like pseudopods Order Heliozoea
3. no movement
1. cylindrical or
bell shaped
bodies
Ciliates – 2. undulating cilia Ciliophora
Peritrich 3. some stalked Order Peritrichida
< .25 mm 4. often colonial i.e. Vorticella sp.
5. attached to
different
substrate
1. no cilia, sticky
Ciliates – tentacles Ciliophora
Suctoria some attached to Order Eridogenida
<.7 mm other organisms i.e. Tokophyra sp.
(i.e. Suctoria)
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3. 1. mostly free
living forms
2. cell of fixed
Ciliophora
Ciliates shape
Order
Paramecium 3. movement by
Oliogohymenophorea
.01 – 4mm contraction and
i.e. Paramecium sp
use of cilia
4. fixed mouth and
anal pore
1. large body
Ciliates Ciliophora
2. contractile
Stentor Orer Heterotrichea
3. cilia on mouth
.01 – 4 mm i.e. Stentor sp.
end
1. barrel-shaped
Ciliates 2. spinous Ciliophora
Coleps projection at Order Prostomatea
.01-4mm posterior end i.e. Coleps sp.
3. cytosome apical
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4. Other fresh water plankton (Animalia, Monera, etc)
Name Picture Characteristic Taxonomy
1. blue green color Kingdom
Blue-green
2. gliding Monera
algae
movement i.e. Annabella
(cyanobacteria)
3. prokaryote sp.
1. sometimes
Phylum
Euglenoids green
Euglenida
<.4mm 2. flagellate
i.e. Euglena sp.
3. red eye spot
1. free swimming
2. tough armor
Dinoflagellates Phylum
3. flagellate
<.4mm Dinoflagellate
4. autotrophic,
heterotrophic
1. corona with cilia
2. hairy
appendages
Phylum Rotifer
3. transparent with
Class
Rotifers lorica
Bdelloided
.4mm - 2 cm 4. free swimming
Class
or attached
Monogononta
5. organs,
compressed
body
1. green brown or
colorless
2. body and Phylum
Hydra
tentacles Cnidaria
2 cm
contract and i.e. Hydra sp.
stretch
3. primitive organs
Phylum
1. flattened
Platyhelminthes
Flatworms 2. eye spots
Class
1-15+ mm 3. move in gliding
Turbellaria
motion
i.e. Planaria sp.
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5. 1. moves in rapid
“s” form
2. round body
Roundworms Phylum
3. bilateral
.2-10 mm Nematodes
4. anterior,
posterior
openings
1. segmented Phylum
Oligochaetes
2. worm motion Annelida
1.5 mm - >2
3. hair bundles Class
cm
(setae) Oligochaeta
1. predatory or
Phylum
Leeches parasitic
Annelida
> 1 cm 2. terminal suckers
Class Hirudinea
3. hermaphroditic
1. mainly benthic
Phylum
2. head bristles
Gastrotricha
Gastrotricha 3. eat algae,
Order
.1-1.5mm bacteria,
Chaetonotida
protozoa
1. head and 4 trunk
Tardigrades
segments
Little water Phylum
2. 4 pair legs
bears Tardigrada
3. eyes
< 1 mm
4. herbivores
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6. Arthropods - segmented, exoskeletons
Name Picture Characteristic Taxonomy
Class
1. bean-like shell
Crustacea
Ostracods 2. filter feeders
Order
<2mm 3. bivalve
Ostracoda
carapace
i.e. Cypris sp.
Class
1. long antennae
Copepods Crustacea
2. tiny eyespot
.5-3mm Order
3. holoplankton
Copepoda
1. antennae Class
2. large compound Crustacea
Water fleas
eye Order
.3-10mm
3. holoplankton Cladocera
i.e. Daphnia sp
1. flattened Class
Isopods
2. 7 pairs legs Crustacea
5-20mm
3. scavengers Order Isopoda
1. curved
Class
2. compressed
Amphipods Crustacea
body
5-25mm Order
3. humped back
Amphipoda
4. scavengers
1. 8 legs
2. round body
Water Class
3. larvae
mites Arachnida
(parasitic)
.5-5mm Order Acarina
4. nymph looks
like adult
1. one tail
Class Insecta
Alderfly 2. long filaments
Order
nymph along the
Megaloptera
5-25mm abdomen
Family Sialidae
3. meroplankton
1. cylindrical case
Caddisfly for protection Class Insecta
larva 2. distinct case but Order
3-40mm different Trichoptera
materials
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7. 1. two jointed tails
Stonefly (cerci) Class Insecta
nymph 2. carnivorous Order
<15 mm 3. indicates clean Plecoptera
water
1. three jointed
Mayfly Class Insecta
tails
nymph Order
2. leaf-like gills on
<15mm Ephemeroptera
sides
1. three leaf like
Damselfly Class Insecta
tail appendages
Nymph Order Odonata
(gills)
<15mm Zygoptera
2. extendable jaws
1. robust
Dragonfly Class Insecta
2. no tail
nymph Order Odonata
appendages
<15mm Anisoptera
3. extendable jaws
Water Class Insecta
1. no jaws
boatman Order
2. tube-like beak
nymph.and Hemiptera
3. nymphs don’t
adult Family
have wings
10-15mm Corixidae
1. strong jaws
2. tough shield
3. fierce predator Class Insecta
Water adult Order
beetle
1. strong jaws Coleoptera
<45mm
2. long segmented Family Elmidae
body
3. short legs
nymph
1. long slender
Mosquito body
Class Insecta
larva 2. moves in
Order Diptera
1-20 mm undulating s
curves
Drawings redrawn from http://www.microscopy-uk.org.uk/pond/index.html
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