Classification of Animals
ICSE Class 7 · Biology · Chapter 3
What this chapter covers
- Kingdom Animalia
- Major invertebrate phyla
- Further phyla
- Two characteristics and two examples per phylum
- Vertebrates
Key points
- Kingdom Animalia contains many-celled organisms with no cell walls that cannot make their own food; most can move.
- Animals without a backbone are invertebrates; animals with a backbone are vertebrates.
- Porifera: body full of pores, fixed to one place; Sycon, Spongilla.
- Cnidaria (Coelenterata): stinging cells, sac-like body with one opening; Hydra, jellyfish.
- Platyhelminthes: flat, unsegmented body, many parasites; tapeworm, liver fluke.
- Nematoda: round body tapering at both ends, gut with two openings; Ascaris, hookworm.
- Annelida: body of ring-like segments, bristles or suckers; earthworm, leech.
- Arthropoda: jointed legs, exoskeleton of chitin shed by moulting; cockroach, crab. It is the largest phylum.
- Mollusca: soft unsegmented body, usually a shell, muscular foot; snail, octopus.
- Echinodermata: spiny skin, tube feet, sea only; starfish, sea urchin.
- Vertebrates have a backbone, an internal skeleton and a skull; they include fishes, amphibians, reptiles, birds and mammals.
- Classify an animal by its characteristics, never by its name or where it lives.
Questions answered
Name two features that every member of Kingdom Animalia shares.
Animals are made of many cells without cell walls, and they cannot make their own food, so they depend on other living things for it.
What is the one feature used to separate invertebrates from vertebrates?
The backbone. Invertebrates do not have a backbone, while vertebrates do.
Why were sponges once mistaken for plants, and why are they now placed among animals?
Adult sponges stay fixed to one place and do not move about, like plants. They are animals because they cannot make their own food and their cells have no cell walls.
Give two characteristics of Phylum Cnidaria.
Cnidarians have stinging cells on their tentacles, and their sac-like body has a single opening, the mouth.
How is the body of a flatworm different from the body of a roundworm?
A flatworm's body is flattened from top to bottom like a ribbon, so it looks like a thin strip. A roundworm's body is round and thread-like, tapering at both ends, so a cut across it shows a circle. Neither body is divided into segments.
Why is the earthworm called the farmer's friend? To which phylum does it belong?
Its burrows let air and water reach plant roots, and its droppings make the soil richer. It belongs to Phylum Annelida.
What is moulting, and why must arthropods moult?
Moulting is the shedding of the old outer covering. Arthropods must moult because their hard exoskeleton cannot grow, so they shed it and form a larger one as they grow.
Name the phylum of each animal: (a) octopus (b) sea urchin (c) Ascaris (d) Spongilla.
(a) Mollusca (b) Echinodermata (c) Nematoda (d) Porifera.