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For teaching the labels

The six animal groups, in plain words

These six are classroom categories, not six scientific classes. They are useful, and each one has animals in this very catalog that break its rule. Knowing which ones is what turns a sorting exercise into a good lesson.

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  • African elephant facing the camera in front of green scrub, its curved tusks and both wide ears clearly visible

    African elephantMammal

  • Barn owl perched on a wooden post against a black background, its pale heart-shaped face turned forward

    Barn owlBird

  • Green sea turtle swimming in shallow turquoise water, seen from above with all four flippers out

    Green sea turtleReptile

  • Red-eyed tree frog on a broad green leaf, one red eye wide open above blue flanks and orange feet

    Red-eyed tree frogAmphibian

  • Two clownfish among the tentacles of a sea anemone, orange bodies crossed by white bands

    ClownfishFish

  • Monarch butterfly resting on green leaves beside clover flowers, wings spread flat, orange panels veined in black and edged with white spots

    Monarch butterflyInvertebrate

One animal from each of the six groups. Photos: African elephant, Bernard DUPONT from FRANCE / CC BY-SA 2.0; barn owl, Charles J. Sharp / CC BY-SA 4.0; green sea turtle, Charles J. Sharp / CC BY-SA 4.0; red-eyed tree frog, Careyjamesbalboa (Carey James Balboa) / Public domain; clownfish, Nick Hobgood / CC BY-SA 3.0; monarch butterfly, Kenneth Dwain Harrelson / CC BY-SA 3.0.

Start with the backbone

One question does most of the work. Does the animal have a backbone?

If it does not, it is an invertebrate, and that is most animals on Earth. If it does, it belongs to one of the five categories below, and the rest of this guide is about telling those five apart.

Even that question has an exception in this catalog. A hagfish has a skull but no true backbone, which leaves it sitting awkwardly on the line. It is filed with the fish, and the Fish section below says so.

Each category below gives what is usually true, then the animals in this catalog that break it. The exceptions are the interesting part. A child who meets a pangolin with an untroubled rule about scales learns the wrong lesson.

Mammals

90 here

Usually: hair or fur, and young that drink milk. The milk is the dependable part.

In the catalog: African elephant, gray wolf, capybara, orca. For dog breeds for a classroom activity, use the separate breed generator.

What breaks the rule here

A platypus and a short-beaked echidna lay eggs. A pangolin is covered in overlapping scales and a nine-banded armadillo in bony bands, and both have only sparse hair underneath. A blue whale, an orca and a West Indian manatee live in the sea. All of them feed their young on milk, which is why all of them are mammals.

  • Platypus swimming at the surface of green water, showing its flat duck-like bill

    PlatypusLays eggs. A mammal.

  • Pangolin walking along a thin branch among leaves, its body and long tail covered in overlapping brown scales

    PangolinCovered in scales. A mammal.

Two of the mammals this section names. Photos: platypus, Charles J. Sharp / CC BY-SA 4.0; pangolin, Frendi Apen Irawan / CC BY-SA 4.0.

Reference: OpenStax Biology 2e: mammals.

Birds

89 here

Usually: feathers. Every bird has them, and no other animal alive today does.

In the catalog: barn owl, emperor penguin, kiwi, ruby-throated hummingbird

The rule holds. Flight is the trap

This is the one category where the simple rule works. Flight is not the rule: an ostrich, an emperor penguin, a kiwi, an emu, a southern cassowary and a greater rhea cannot fly. A common vampire bat flies well and is a mammal.

  • Two adult emperor penguins on snow with a small grey downy chick standing between them

    Emperor penguinCannot fly. A bird.

  • Ostrich male walking over rocky ground among dead trees, black body feathers, white wing tips and long bare legs

    OstrichCannot fly. A bird.

Two of the birds this section names. Photos: emperor penguin, Ian Duffy from UK / CC BY 2.0; ostrich, Frank Vassen from Brussels, Belgium / CC BY 2.0.

Reference: OpenStax Biology 2e: birds.

Reptiles

62 here

Usually: scales, air breathing, and eggs laid on land. Lizards, snakes, turtles and crocodiles all sit here.

In the catalog: Komodo dragon, king cobra, green sea turtle, American alligator

What breaks the rule here

A boa constrictor, a green anaconda and an adder give birth to live young. And scales alone settle nothing: a pangolin is covered in them and is a mammal.

  • Green anaconda coiled on red soil, olive-green body marked with large dark oval spots and its head resting low

    Green anacondaGives birth to live young.

  • Boa constrictors coiled together on a rock ledge, patterned in tan and brown saddles

    Boa constrictorGives birth to live young.

Two of the reptiles this section names. Photos: green anaconda, MKAMPIS / CC BY-SA 4.0; boa constrictor, Pavel Ševela / CC BY-SA 4.0.

Reference: OpenStax Biology 2e: reptiles.

Amphibians

46 here

Usually: bare skin with no scales, young that live in water, adults that come out onto land.

In the catalog: common frog, fire salamander, axolotl, great crested newt

What breaks the rule here

An axolotl, an olm, a hellbender, a siren and a mudpuppy never make the move to land. They stay in the water for life. An amphiuma mostly does too, though it can cross land and lays its eggs in damp ground. Note also that skin is something to look at in a photograph, not something to test by touching an animal you do not know.

  • Axolotl resting on pale gravel in green water, the feathery gills fanned out behind its wide flat head

    AxolotlStays in the water for life.

  • Olm, a pale pink cave salamander with a long thin body, swimming in dark water

    OlmStays in the water for life.

Two of the amphibians this section names. Photos: axolotl, LoKiLeCh / CC BY-SA 3.0; olm, Arne Hodalič / CC BY-SA 3.0.

Reference: OpenStax Biology 2e: amphibians.

Fish

71 here

Usually: gills, fins, and a whole life spent in water.

In the catalog: great white shark, clownfish, lined seahorse, moray eel

What breaks the rule here

A mudskipper walks about on mud and spends hours out of the water. A lungfish breathes air. A flying fish leaves the water altogether. A hagfish strains the backbone question itself: it has a skull but no true backbone, only small vertebra-like nodules of cartilage, so the first test in this guide cannot place it cleanly. It is filed here with the fish. The names mislead too: a whale shark is a fish and a blue whale is a mammal, while jellyfish, cuttlefish, crayfish and starfish are not fish at all.

  • Two mudskippers with bulging eyes resting on a reddish rock out of the water

    MudskipperSpends hours out of the water.

  • Lungfish with a long olive body and paddle fins lying on gravel near water plants

    LungfishBreathes air.

Two of the fish this section names. Photos: mudskipper, Bjørn Christian Tørrissen / CC BY-SA 4.0; lungfish, Mitch Ames / CC BY-SA 4.0.

Reference: OpenStax Biology 2e: fishes.

Invertebrates

90 here

No backbone. That is the whole of it.

In the catalog: giant Pacific octopus, honey bee, garden snail, sea urchin

Not really one kind of animal

An octopus and a honey bee have almost nothing in common. They share a label because of something they both lack. Most animals on Earth are in here, and the other five categories are the exceptions.

  • Giant Pacific octopus spreading its arms in an aquarium, rows of pale suckers on reddish skin

    Giant Pacific octopusNo backbone.

  • Honey bee with striped orange and black body gathering pollen on small white flowers

    Honey beeNo backbone.

Two of the invertebrates this section names. Photos: giant Pacific octopus, Cliff from Arlington, Virginia, USA / CC BY 2.0; honey bee, Didier Descouens / CC BY-SA 4.0.

Reference: OpenStax Biology 2e: animal diversity.

A sorting guide, not a test

Work down the list and stop at the first yes. It will place most animals, and it is a guide rather than a test, because some animals genuinely do not fit.

  1. No backbone? It is an invertebrate.
  2. Feathers? It is a bird.
  3. Drinks milk as a baby? It is a mammal.
  4. Bare skin, and young that live in water? It is an amphibian.
  5. Scales, and it breathes air on land? It is a reptile.
  6. Gills and fins for the whole of life? It is a fish.
1. No backbone?yesInvertebratesno2. Feathers?yesBirdsno3. Drinks milk as a baby?yesMammalsno4. Bare skin, young in water?yesAmphibiansno5. Scales, breathes air on land?yesReptilesno6. Gills and fins all its life?yesFishnoStill no fit? The scheme ran out. Talk about why.
The six questions above as a tree. Stop at the first yes.

Milk comes before scales on purpose. Ask about scales first and a pangolin ends up a reptile.

When an animal will not fit, that is the scheme running out, not the child getting it wrong. Show the group label the generator gives, and talk about why the rule missed it. A mudskipper is worth five minutes of anyone’s lesson.

Background reference: ITIS for the catalog-wide group labels.

Where these labels stop

Worth saying out loud to an older class, because a sharp child will find the seam without help.

  • Only some of these six are formal groups in biology. Mammals, birds and amphibians are, and so are reptiles, with the catch below. Fish and invertebrates are not: they are convenient bundles.
  • Fish are not one branch. A great white shark has a skeleton of cartilage and an Atlantic salmon has one of bone. They are further apart from each other than a salmon is from a gray wolf.
  • Invertebrate is defined by an absence, which is why an octopus and a honey bee share a label.
  • Reptiles as taught in class leave out birds, although in modern biology birds sit inside the reptile branch. The classroom six are a ladder, and it is fine to say so while children are climbing it.

Reference: OpenStax Biology 2e, animal diversity and the catalog’s methodology.

Using this with the generator

  1. Leave the group filter on All 448.
  2. Enter the number of children.
  3. Select Generate.
  4. Hide the coloured group labels from the children.
  5. Ask each child to sort their animal with the list above.
  6. Show the labels and compare.
  7. Collect the animals that did not fit and discuss them.

All 448 animals carry one of these six labels. The labels were checked as a whole against Integrated Taxonomic Information System (ITIS), not animal by animal. all 448 animals is the page that says exactly how far that checking goes.

Step two above assumes one animal per child and no two the same, which is a harder thing to arrange than it sounds. One animal per child, and why that matters covers the class that is bigger than the group you filtered to, and the two classes you have to run on the same day.

Sorting is a quiet exercise. If the room needs a loud one, animal charades that work for any age uses the same six groups as its teams, and a child who has to act a hagfish has to know what one is.

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