Invertebrates
Invertebrates are animals that lack a backbone or vertebral column. These animals make up over 98% of all known animal species on Earth. Unlike vertebrates, they do not have an internal skeleton made of bone, though some may have other forms of structural support like hard outer shells or hydrostatic skeletons
Key Characteristics of Invertebrates
- No backbone or spinal cord
- Can be found in nearly all ecosystems (land, water, air)
- May have a hard external skeleton (exoskeleton) or fluid-filled internal support (hydrostatic skeleton)
- Reproduce in diverse ways – many lay eggs
- Highly diverse body structures and organ systems
Major Groups of Invertebrates
Protozoa
- Unicellular (single-celled) organisms
- Microscopic in size and mostly found in aquatic environments
- Capable of breathing, movement, and reproduction
- Examples: Amoeba, Paramecium, Flagellates
Flatworms
- Soft-bodied, bilaterally symmetrical animals
- Usually parasitic, such as tapeworms and liver flukes
- Lack complex organ systems
Annelids (Segmented Worms)
- Have segmented bodies
- Possess well-developed internal organs
- Found worldwide — in soil, freshwater, and marine environments
- Examples: Earthworms, Leeches, Roundworms
Mollusks
- Have soft bodies, often enclosed in a hard external shell
- Can live on land (e.g., snail, slug) or in water (e.g., oyster, clam, squid, octopus)
Echinoderms
- Exclusively marine animals
- Possess spiny skin or arms radiating from the center
- Examples: Sea stars, Sea urchins, Sea cucumbers
Coelenterates (Cnidarians)
- Soft-bodied aquatic animals with stinging tentacles
- Mostly radially symmetrical
- Examples: Jellyfish, Sea anemones, Corals
Arthropods
- The largest phylum in the animal kingdom
- Have a hard exoskeleton and jointed legs
- Divided into four major sub-groups:
1.Insects
- Body has three parts: head, thorax, abdomen
- Six legs and usually wings
- Examples: Bees, Butterflies, Ladybir
2.Arachnids
- Have eight legs and two body parts
- No antennae
- Examples: Spiders, Scorpions
3. Crustaceans
- Mostly aquatic
- Have a hard outer shell, multiple legs, and antennae
- Examples: Crabs, Lobsters, Barnacle
4.Myriapods
- Long, segmented bodies with many legs
- Examples: Centipedes, Millipedes