Protozoa are single celled organisms that are very diverse groups. Of the existing protozoa, there are about 21,000 species that occur as free-living in a variety of habitats while another 11,000 species occur as parasitic microbes in both vertebrate and invertebrates hosts.

Invertebrates are multi-cellular animals without a backbone or bony skeleton. This is by far the largest group in the animal kingdom: 97% of all animals are invertebrates. Worldwide in distribution, they include animals as diverse as sea stars, sea urchins, earthworms, sponges, jellyfish, lobsters, crabs, insects, spiders, snails, clams, and squid. Invertebrates are especially important as agricultural pests, parasites, or agents for the transmission of parasitic infections to humans and other vertebrates. Invertebrates serve as food for humans and are key elements in food chains that support birds, fish, and many other vertebrate species.

bdelloid rotifer
Acanthocystis heliozoan
amoeba
ant
aphid feeding
badger lice
bedbug
bee mite
beemoth
beetle antenna
biological control wasp
bird eating spider
biting midge
bluebottle
bluebottle eye
boxwood psyllid larvae
brochosomes on leafhopper
Caenorhabditis elegans worm
Calcarina dinoflagellate
carpet beetle
cat flea
Cat flea
Caterpillar
Chaetonotus gastrotrich egg
clothes moth
dead fly
didinium protozoan
dinoflagellate
dinoflagellates
dragonfly male genitalia
dung fly
dust mite
euplotes protozoa and diatoms
euplotes protozoan
eye lash mites
eyelash mites
firefly
fish louse
flying ant
fruit flies
gapeworm
head louse
holosticha protozoan
human flea
hydra
indian spider
ixodes female tick
lacewing larva
ladybird
ladybird foot
lily beetle
maggot
mange mites
march fly
midge mouthparts
millipede
minnow ciliate protozoan
mosquito
mosquito foot
mosquito pupae
moth
moth proboscis
moth wing scales
rabbit flea
radiolaria
radiolarian
scale insect
scorpion
scorpion fly
sea cucumber ossicle
silver fish
small parasitic wasp
solomon seal sawfly larva
spider
spider mite
spider silk
spiderling and silk
spiderling hatching
spiney spider
sponge
springtail
springtail
springtail skin
starfish
stick insect foot
tapeworm
tapeworm
tardigrade
tardigrade
termite
thrip
thrip
tick
tick mouthparts
tropical ant
tubifex worm
wasp
wasp larvae
wasp tongue
water boatman
water sprintgail
water sprintgail eyes
weevil
weevil
woodlouse
woodworm
worm