Arthropods, mollusks, echinoderms, Cnidarians


An arthropod is an animal that has a jointed exoskeleton

One kind of arthropods are lobsters, crabs,



exoskeleton covers and protects body and gives it support

jointed legs

jointed body

digestive system with 2 openings

circulatory system and a brain

molts so exoskeleton can grow with animal

well developed organs for site, sound and touch


Lobsters - legs are adapted to catch prey and carry to mouth. Lobsters claws crush shells of oysters or clams and are 2 sizes for defense and tearing food.

Arachnids - many have sharp body parts that inject poison

Tarantulas - legs are evenly spaced for balance while walking and climbing

Grasshoppers - mouths are adapted for crushing food and back legs are powerful for jumping.


A mollusk is an animal with a soft body and no bones.

Example: clams, oysters, slugs, snails, squids and octopods


some have a hard shell that protects their body

Mantle - shell of mollusk, produces material to harden shell, grows as animal grows

some the mantle is a tough layer of skin

muscular foot - helps move and burrow into ocean floor

reproduce sexually

some have bivalves like oysters and clams

Radula - organ in snail that acts like a tongue with sharp teeth

octopus and squid have well developed brains and nervous systems

Adaptations - octopus and squid have jet like motion and squirt ink, snail has has a hard shell that protects itself.


Cnidarians have the ability to sting its prey, carnivorous animals, or meat-eating, poison in tentacles.


tentacles that sting its predators and bring food to mouth (digestive system)

waste leaves through mouth

no organs, cells organized instead of tissues, outer layer is protection and inner layer is used for digestion

live in water

radial symmetry

Polyp or Medusa Form

reproduce sexually and asexually

Adaptation - coral produces a skeleton to protect its soft body; some sting its predators with tentacles

What characteristics do all cnidarians have in common? They all have tentacles, are carnivores, have radial symmetry, have stinging cells, and live in water.


Echinoderms are invertebrates that have internal skeletons and spines sticking out from their bodies

examples: starfish, sand dollars, sea urchins, sea cucumbers


Interval skeletons and spines

live only in the ocean

get oxygen from seawater

most adults appear to have radial symmetry

spiny skin


no head or brain

tube feet

Reproduce sexually and asexually

Adaptation - Mouth is at the center of underside with powerful jaws and hidden among their spines and poison glands. They also have tube feet for moving, feeding and sensing respiration