Karthikeyan

• Multicellular organisms

• Cells do not have cell walls or chloroplasts

• Feed by ingesting solid food and digesting it internally

Classification of Animals

• Animals are divided into groups called phyla

• Two important phyla discussed here:

  • Arthropods

  • Vertebrates

• Animals without a backbone are called invertebrates (not a true scientific group, but a useful term)

Arthropods

Meaning: Arthropod = jointed limbs

Common Features

• Jointed legs

• Hard exoskeleton (cuticle)

• Segmented body

• Flexible joints for movement

Body usually divided into:

• Head

• Thorax

• Abdomen

Classes of Arthropods

1. Crustacea

Examples: crabs, shrimps, lobsters, woodliceKey features:

• Exoskeleton and jointed limbs

• Two pairs of antennae

• Compound eyes (many lenses, good at detecting movement)

• Mostly aquatic (some live on land)

2. Insects

Examples: butterflies, mosquitoes, beetles, fliesKey features:

• Body divided into head, thorax, abdomen

• Three pairs of legs

• One pair of antennae

• Usually two pairs of wings

• No legs on the abdomen

• Cuticle prevents water loss → helps them survive on land

3. Arachnids

Examples: spiders, scorpions, ticksKey features:

• Body divided into cephalothorax + abdomen

• Four pairs of legs

• No antennae

• Several simple eyes

• Pedipalps used for feeding and reproduction

• Some inject poison to paralyse prey

4. Myriapods

Examples: centipedes and millipedesKey features:

• Head + long segmented body

• One pair of antennae

• Simple eyes

• Many legs

• Centipedes: carnivores

• Millipedes: herbivores

• Millipedes appear to have two pairs of legs per segment