The New Childrens Encyclopedia

LIVING WORLD

In a classification tree of the animal kingdom ( p. 84–85), there is no

group called invertebrates. There is one called vertebrates (it is part of the

chordates phylum and is split into mammals, birds, etc.)—but there are

more than 30 different main groups of invertebrate, including:

INVERTEBRATE GROUPS

 SPONGES (5,000–10,000 species)

It was once thought that sponges were

plants, but they are simple animals. They

are fixed to the seabed and filter food

from the water as it washes over them.

 ANNELIDSearthworms,

leeches, polychaetes (12,000 species)

Annelid worms have bodies that are

divided into segments.

 ECHINODERMSstarfish, sea

urchins, sea cucumbers (7,000 species)

Nearly all echinoderms live on the

seafloor. They have spiny bodies, which

are usually divided into five equal parts.

 CNIDARIANSjellyfish, corals,

hydras (8,000–9,000 species) All

cnidarians have basic bodies with

stinging tentacles, a very simple nervous

system, and just one opening: the mouth.

 ARTHROPODSinsects,

arachnids, crustaceans (1,000,000

species) Arthropods, such as this beetle,

have an exoskeleton—a hard outer

cover. Their exoskeleton and body are

divided into parts.

 MOLLUSKSsquid, snails,

bivalves (50,000 species) Squid, slugs,

and oysters are all mollusks. Most

mollusks have a shell and a radula—a

ribbonlike “tongue” covered in scaly

denticles.

Making sense

Simple invertebrates, such as sea anemones, have

simple senses: they can detect food and reach

toward it, and they can sense danger and shrink

from it. More advanced invertebrates have superior

senses. Flies see lots

of images through

compound eyes, so

they can notice the

slightest movement;

and grasshoppers

have eardrums in

their abdomens.

WITHOUT

INVERTEBRATES, the planet

would not survive. Krill (a type of

crustacean) form the basis of the

food chain in polar seas. Insects such

as ants and beetles, and their larvae,

help clean up the planet. Other

insects, such as bees, are essential

for pollination ( p. 90-91).

 KRILL

Without krill, entire species of fish

would disappear. These tiny creatures

form the main part of many marine

animals’ diets, including the whale

shark, the world’s biggest fish.

 ANTS

Decomposers such as

ants break up dead

animals and plants.

The pieces that aren’t

eaten are more easily

absorbed into the

ground, releasing

nutrients for plants.

 DUNG BEETLE

Without dung beetles rolling away

animal droppings, all kinds of places

from African savannas to Australian

farmland would be knee-deep

in dung. Less dung means

fewer places for flies to

breed, so there are

fewer fly-borne

diseases.

 BUTTERFLIES can

taste with their feet.

Chemical sensors on the

insect’s feet “taste” what

it lands on, so it knows

if it’s standing on

something it can drink,

such as nectar.

INVERTEBRATES