Invertebrates Overview

Invertebrates

• Invertebrates make up 95% of known organisms in the animal kingdom.
• They are multicellular and lack a backbone.
• They are divided into six groups: Porifera, Coelenterates, Worms, Mollusks, Arthropods, and Echinoderms.

Porifera (Sponges)

• Unusual organisms resembling plants.
• Simple body structure; no tissues or organs, brain, head, blood, or muscles.
• Vary in color, size, and shape.
• Can live a long time, with few predators.
• Some produce toxins for protection.
• Aquatic; some freshwater, others saltwater.
• Young sponges are mobile larvae.
• Adults remain stationary.
• Absorb water and oxygen through pores, and release waste.

Coelenterates (e.g., sea anemone, fan coral)

• Aquatic invertebrates, mostly marine.
• Have a central opening for feeding surrounded by tentacles.
• Simple nervous system.
• Reproduce sexually or asexually.
• Many produce toxins for protection, which can be harmful to humans.
• Examples include jellyfish, sea anemones, and corals.

Worms

• Invertebrate animals with long, soft bodies.
• Some have ring-like divisions.
• Lack limbs; move by sliding or contracting.
• Abundant in various environments (underground, water, humid places).
• Lack lungs; breathe through their skin.
• Predators include birds and salamanders.
• Important role in soil health; eat and decompose organic matter (plants, dead animals, bacteria, fungi).
• Reproduce sexually or asexually.

Mollusks (e.g., slugs, squid)

• Soft-bodied animals, some with hard shells for protection.
• Can live on land and in the sea.
• Some have one shell (e.g., queen conch, garden snails), others have two shells (e.g., clams).
• Some have no shell (e.g., slugs).

Arthropods

• Make up around 75% of animals.
• Characterized by an exoskeleton.
• Bodies divided into segments.
• Legs and appendages with joints.
• Cold-blooded.
• Can live in water, on land, or fly.
• Good eyesight and hearing.
• Use antennae for sensing.
• Four subgroups: insects, arachnids, crustaceans, and myriapods.

Insects (e.g., wasps, beetles, ants, butterflies)

• Typically have six legs, two antennae, and eyes on each side of their heads.
• Some insects produce toxins (e.g., bees).

Arachnids (e.g., scorpions, spiders, ticks)

• Eight legs.
• No antennae.
• Bodies divided into cephalothorax and abdomen.
• Venomous in some species.

Crustaceans (e.g., lobsters, shrimp, crabs)

• Mostly aquatic.
• Bodies divided into cephalothorax and abdomen.
• Strong shell.
• Two antennae and typically have 10 legs, with some having functional pincers.

Myriapods (e.g., centipedes, millipedes)

• Many legs; each body segment with two legs.
• Two antennae.
• Some are venomous.

Echinoderms (e.g., starfish, sea lilies, sea urchins)

• Star or round shape, lack a head.
• Have feet for movement on sea floors.
• Internal skeleton of calcareous plates (e.g., spikes).
• Reproduce sexually, with larval stage.
• Live in water.
• Have around 7000 species.
• Lack heart and blood.
• Move with arms.