Biology · Lesson 5

Animal kingdom: invertebrates & vertebrates

JAMBWAECNECO

What the syllabus asks

JAMB: variety of organisms: diversity of animals, characteristics of major phyla and classes, adaptations

WAEC: classification of living things; Kingdom Animalia: invertebrates (Protozoa as an animal-like protist, Porifera, Coelenterata/Cnidaria, Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda: Insecta, Crustacea, Arachnida, Myriapoda; Echinodermata); Chordata: Pisces, Amphibia, Reptilia, Aves, Mammalia; characteristic features, examples and economic importance; metamorphosis in insects

NECO: classification of living things; Kingdom Animalia: invertebrates (Protozoa as an animal-like protist, Porifera, Coelenterata/Cnidaria, Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda: Insecta, Crustacea, Arachnida, Myriapoda; Echinodermata); Chordata: Pisces, Amphibia, Reptilia, Aves, Mammalia; characteristic features, examples and economic importance; metamorphosis in insects

What you will learn

State the general characteristics of animals and explain the hierarchy of classification.
Use binomial nomenclature correctly.
Describe the distinguishing features of the main invertebrate phyla with examples.
Distinguish the four main classes of arthropods.
Describe complete and incomplete metamorphosis in insects.
State the characteristic features of the five vertebrate classes, with Nigerian examples.
Explain the economic importance of selected animals and identify unknown animals from their features.

Key points

Animals: multicellular heterotrophs without cell walls; hierarchy Kingdom → Phylum → Class → Order → Family → Genus → Species.
Binomial name: Genus (capital) species (lower case), italicised, e.g. Homo sapiens.
Cnidarians: two layers, radial symmetry, tentacles with stinging cells, one opening (Hydra).
Flatworms: flat, mostly hermaphrodite parasites (tapeworm, liver fluke, Schistosoma); roundworms: round, mouth and anus (Ascaris, hookworm).
Annelids: segmented with chaetae and coelom (earthworm); molluscs: soft body, foot, mantle, shell (snail); echinoderms: spiny skin, tube feet (starfish).
Arthropods: jointed legs, chitin exoskeleton, open blood system, moulting.
Insects 3 parts/6 legs/1 pair antennae; arachnids 2 parts/8 legs/no antennae; crustaceans 2 pairs antennae, gills; myriapods many legs.
Complete metamorphosis: egg–larva–pupa–adult (housefly, mosquito); incomplete: egg–nymph–adult (cockroach, grasshopper).
Fish: scales, gills, fins, 2-chambered heart; amphibians: moist skin, 3 chambers; reptiles: dry scales, leathery eggs.
Birds: feathers, beak, hollow bones, warm-blooded; mammals: hair, mammary glands, diaphragm, 4-chambered heart.

Start here: What makes an animal, and why we classify

There are well over a million known species of animal, from microscopic worms in the soil of your school farm to the elephants of Yankari Game Reserve. To study such variety, biologists sort living things into groups. This is classification.

Characteristics of animals (Kingdom Animalia): multicellular; cells have no cell wall and no chloroplasts; heterotrophic (they eat ready-made food); most can move from place to place; most have nervous systems and respond quickly; growth is usually limited (they stop growing at maturity); they store carbohydrate as glycogen.

Classification uses a hierarchy of groups, from the largest to the smallest:

Kingdom → Phylum → Class → Order → Family → Genus → Species

A memory aid: "King Philip Came Over For Good Soup." As you go down the hierarchy, the members of each group share more features. A species is a group of organisms that can interbreed to produce fertile offspring.

Rank	Human	Domestic dog
Kingdom	Animalia	Animalia
Phylum	Chordata	Chordata
Class	Mammalia	Mammalia
Order	Primates	Carnivora
Family	Hominidae	Canidae
Genus	Homo	Canis
Species	sapiens	familiaris (often written lupus familiaris)

Binomial nomenclature

Carl Linnaeus introduced the two-name system. The genus name comes first with a capital letter, the species name second in lower case, and both are written in italics (or underlined separately when handwritten): Homo sapiens, Musca domestica (housefly), Clarias gariepinus (African catfish).

Worked example 5.1

Which is correctly written? A. Homo Sapiens B. homo sapiens C. Homo sapiens D. Sapiens homo

Genus first with a capital: Homo. Species second in lower case: sapiens.
Both italicised (or underlined).

⚠️ Common mistake: capitalising the species name. Only the genus takes a capital.

Try it yourself. Which two ranks make up the scientific name of an organism?

Show solution

Genus and species.

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Practice questions

1. Which of these is an arthropod?

Grasshopper
Earthworm
Tapeworm
Snail

Show answer

A: Grasshopper
Jointed legs and an exoskeleton.

2. Insects have

four pairs of legs
no legs
many pairs of legs
three pairs of legs

Show answer

D: three pairs of legs
Six legs on the thorax.

3. Spiders belong to the class

Crustacea
Myriapoda
Arachnida
Insecta

Show answer

C: Arachnida
Four pairs of legs.

4. The earthworm belongs to the phylum

Mollusca
Annelida
Arthropoda
Nematoda

Show answer

B: Annelida
Segmented worms.

5. Snails belong to the phylum

Mollusca
Annelida
Arthropoda
Coelenterata

Show answer

A: Mollusca
Soft bodies, usually with a shell.

Key words

Classification: Arranging organisms into groups based on similarities and differences.
Taxonomy: The science of naming, describing and classifying organisms.
Binomial nomenclature: Naming an organism with two Latin words: genus and species, e.g. Homo sapiens.
Phylum: A major group within a kingdom, e.g. Arthropoda.
Invertebrate: An animal without a backbone (vertebral column).
Vertebrate: An animal with a backbone made of vertebrae.
Exoskeleton: A hard outer skeleton; in arthropods it is made of chitin.
Ecdysis (moulting): Shedding of the exoskeleton to allow growth.
Metamorphosis: A change in body form during development, e.g. larva to adult.
Coelom: A fluid-filled body cavity lined with mesoderm.
Poikilothermic: Having a body temperature that varies with the surroundings ("cold-blooded").
Homoiothermic: Keeping a constant body temperature ("warm-blooded").

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