What it does
The animal kingdom has millions of species, but a few questions about body plan sort them into a handful of large groups called phyla. This page turns those questions into a branching key, drawn as a tree:
- Level of organisation: are the cells only loosely together (sponges), or do they form tissues and organs?
- Symmetry: radial (like a wheel) or bilateral (left and right halves)?
- Germ layers: two (diploblastic) or three (triploblastic)?
- Body cavity: none, a false cavity (pseudocoelom) or a true coelom?
- Notochord: a stiff rod along the back, at least in the embryo?
- Jointed legs with a hard exoskeleton, and ring-like segments.
The answers lead to 11 phyla: Porifera, Cnidaria, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata and Chordata. Each ends with a one-line summary of its main features.
It fits the Class 11 biology chapter on the animal kingdom, and the Class 9 chapter on diversity. Start one level up with the five-kingdom sorter sorter; to write a key of your own for any group, use the dichotomous key builder, and follow single species from kingdom to species on the taxonomy ladder.
How to use it
- Answer the questions yourself. Each card gives the question, a short explanation of the words in it, and the possible answers. Tap one; the next question appears and the tree lights up your path. Back one step undoes the last answer, Start again clears them all.
- Pick an animal from the list (20 examples, from a bath sponge to a human). The key walks it all the way, lists each answer in words and names the phylum.
- In the tree, numbered circles are the questions (Q1 to Q8), the orange one is the question you are on, and the blue line is your path. The phyla sit on the right.
Worked example
Pick Starfish. The path reads:
- How are the cells organised? Tissues or organs.
- What symmetry does the adult body have? Radial.
- How many germ layers form the body? Three (triploblastic).
The title says Phylum Echinodermata, and the summary explains: spiny skin, radial adults with bilateral larvae, a water vascular system with tube feet, all marine. The jellyfish shares the first two answers but has only two germ layers, which sends it to Cnidaria instead.
Now pick Earthworm: tissues, bilateral, true coelom, no notochord, no jointed legs, ring segments: Annelida. The roundworm Ascaris stops earlier, at the false body cavity: Aschelminthes.
Tips
- Symmetry is about the adult. Starfish larvae are bilateral, which is one clue that echinoderms are closer to us than to jellyfish.
- “Worm” is not a phylum: flatworms, roundworms, segmented worms and acorn worms sit in four different phyla.
- Chordates (and hemichordates) are often taught as a separate group of the key; this page keeps them in the same tree so you can see where they branch off.
FAQ
Why is the order of questions this one? The early questions separate the biggest, oldest splits in animal body plans; later ones split closer relatives. Other keys use a different order and reach the same phyla.
Where are insects, crabs and spiders? All in Arthropoda, the largest phylum. Snails, octopuses and mussels are in Mollusca.
Is anything stored? No. Everything runs in your browser. fibub is not part of NCERT; the topics follow the syllabus, but the words, key and examples are our own.
Where the numbers come from
- The basis of animal classification (levels of organisation, symmetry, germ layers, coelom, notochord, segmentation) and the features of the major phyla are standard zoology. The key, the wording and the choice of examples are fibub's own; no textbook text, figures or tables are copied.
- A teaching model: real keys use many more characters, and some groups (for example Aschelminthes) are now split differently.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.