Classification of Animals:
Invertebrate Animals 6 th Grade Science
Animal Characteristics Many-celled organisms sharing similar features and that are made of different kinds of cells.
Animal cells have a nucleus and organelles surrounded by a membrane – EUKARYOTIC.
Cannot make their own food – HETEROTROPHIC – digest their food.
Can move from place to place to find food, shelter, and mates, and to escape from predators.
Symmetry Symmetry: arrangement of the individual parts of an object Radial: body parts arranged in a circle around a central point Bilateral: parts are mirror images of each other Asymmetrical: bodies cannot be divided into matching halves
Animal Classification Invertebrates ( No backbone)
Cnidarians Sponges Roundworms Annelids Echinoderms Chordates Flatworms Mollusks Arthropods
What is an Invertebrate?
Invertebrates are animals that do not have backbones.
97% of the animal kingdom is made up of invertebrates.
Some can be found in ponds, oceans, and other water environments.
Insects and some other invertebrates have exoskeletons.
An exoskeleton is a hard outer covering that protects an animal’s body and gives it shape.
Porifera Characteristics They live in water. (Most are found in the ocean.) They look like plants but they are animals.
Sponges stay fixed in one place -
Their bodies are full of pores and their skeleton is made of spiky fibers (spicules) or rubbery spongin Sponges are divided into classes according to the type of spicule they have – 5,000 species identified!
Porifera Characteristics Sponges can reproduce asexually through budding ~
a new sponge grows from pieces of an old sponge Most sponges that reproduce sexually are hermaphrodites, meaning they have both eggs and sperm Sperm is released into water Sperm floats until they are drawn into another sponge where they fertilize an egg Larva develops in sponge, leaves sponge, and settles to the bottom where it grows into an adult
Cnidaria: Corals, Hydras, and Jellyfish
Cnidaria Characteristics Cnidaria comes for the Greek word for nettle.
All cnidarians have stinging cells called
in tentacles surrounding their mouths.
Cnidarians are more complex than sponges.
They have complex tissues, a gut for digesting food, and a nervous system.
They come in two body shapes, the medusa and the polyp.
Polyp: usually sessile and vase-shaped Medusa: free-swimming and bell-shaped
Cnidaria Characteristics Cnidarians reproduce both sexually and asexually Polyp forms reproduce asexually by budding Some polyps also reproduce sexually be releasing sperm or eggs Medusa forms have a two-stage life cycle in which they reproduce both sexually and asexually
Sea Anenomes and Corals They are polyps their entire life.
They look like brightly colored flowers.
They live in colonies.
They have soft tube-like bodies with a single opening surrounded by arm-like parts called tentacles.
They feed by catching tiny animals in their tentacles.
Hydras They live in fresh water.
They spend their entire life as polyps.
Hydras have tentacles that catch their food.
They move from place to place.
Hydras are very small animals.
Reproduce asexually by budding.
Jellyfish They spend most of their life as medusa.
Jellyfish catch shrimp, fish, and other animals in its tentacles also.
Reproduces sexually to produce polyps; then each polyp reproduces asexually to form new meduae.
Worms Flatworms Roundworms Segmented Worms
Platyhelminthes: Flatworms Search for their food; long, flattened bodies with organs and systems They have a head and a tail, and flattened bodies –
Planaria – free-living Tapeworms – parasitic; each segment (proglottid) contains sperm and eggs (reproduce sexually) ~ when fertilized eggs fill segment, it breaks off and passes out with wastes of host – can be up to 80,000 eggs per segment!!! Lack a digestive system and absorb nutrients from the host’s intestine
Nematoda: Roundworms They have rounded bodies; body is a tube within a tube; I.e., digestive tract has both a mouth and an anus They live in damp places and they can also live inside humans and other animals.
Heartworm (Dirofilaria immitis) ~ Passed by mosquito bite They too can make people and other animals sick.
Diets vary with some roundworms being decomposeers, some predators, and some parasites Most wide-spread animal on earth!
Annelida: Segmented Worms The earthworm (oligochaete), leech (hirudinea), and marine worm (polychaete) belong to this group.
Their bodies are divided into repeating segments Each segment has nerve cells, blood vessels, part of the digestive tract, and the coelom (body cavity) Closed circulatory system and complete digestive system with two body openings They prefer burrowing through moist soil.
This allows them to move easily and it keeps them from drying out.
Annelida: Segmented Worms Earthworms – have more than 100 body segments Use external bristle-like setae and muscles to move Eat organic material in soil Exchange carbon dioxide and oxygen through mucus-covered skin
Annelida: Segmented Worms Leeches Have flat bodies with sucking disks at both ends Can store enormous amounts of food for months Secrete heparin, which prevents blood from clotting
Annelida: Segmented Worms Marine worms – use bristles or setae for moving Some are filter feeders Some eat plants or rotting material Some are predators or parasites
Mollusca: Octopi, Squid, Slugs, Snails, and Bivalves A mollusk has a soft body usually covered by a hard shell, a rough tongue (radula), a muscular foot, and a mantle (thin layer of tissue that covers the mollusk’s soft body and secretes the shell).
Aquatic mollusks have gills for gas exchange; land mollusks have lungs A snail is a mollusk with a single hard shell.
A clam has two shells joined together by a hinge.
Squids and octopi are also mollusks.
Their hard shells are small, but they are inside their bodies.
Characteristics of Mollusks Mantle: tissue that covers a mollusk’s soft body and that may produce a shell Lungs or gills: exchange carbon dioxide from the animal for oxygen in the air or water Many mollusks use a radula, a scratchy tongue-like organ, to help them eat Some have an open circulatory system which washed blood over organs and lacks blood vessels
Types of Mollusks Gastropods – most have one shell Live in water or on land Move by gliding their large muscular foot along a trail of mucus
Gastropods: Slugs and Snails
Types of Mollusks Bivalves – have two shells Large muscles open and close shell halves Water animals that filter feed Use gills to remove foot from water
Bivalves: Clams and other two shelled shellfish
Types of Mollusks Cephalopods – have no external shell Have a foot divided into tentacles with suckers Move by using a mantle to quickly squeeze water through a funnel-like siphon Have a closed circulatory system with blood vessels
Cephalopods: Octopi and Squid
Arthropoda: Insects, Spiders, Ticks, Mites, Centipedes, Millipedes, Crustaceans
Arthropoda Characteristics Arthropods are a group of invertebrates with jointed appendages, such as claws, legs, and antennae, and a hard exoskeleton that protects the arthropod; also have bilateral symmetry.
More than a million species of arthropods have been discovered!!
As it grows, it
or sheds its old exoskeleton.
Then it grows a new exoskeleton that allows its body to continue to grow.
The largest group of arthropods are insects.
Insect Characteristics Insects have adapted to living almost everywhere! Over 700,000 species have been classified….so far!!
An insect’s body has 3 parts: the head, thorax, and abdomen.
The head has one pair of antennae and two compound eyes ~ well- developed sense organs.
Thorax has three pairs of jointed legs and usually one or two pairs of wings.
Reproductive organs are located in abdomen.
Open circulatory system; oxygen enters through openings on sides called spiracles
Insect Metamorphosis Complete Metamorphosis
Insect Metamorphosis Incomplete Metamorphosis
Arachnids: Spiders, Scorpions, Ticks, and Mites They have 2 main body parts: a cephalothorax and an abdomen The thorax has 4 pairs of jointed legs; no antennae.
They do have special mouth parts like fangs.
They kill more insect pests than any other animal.
Myriapods: Centipedes and Millipedes Centipedes use their many legs to run from enemies (one pair of jointed legs attached to each segment).
Millipedes roll up their bodies when they sense danger approaching (two pairs of jointed legs attached to each segment).
Feed on plants.
Crustaceans: Shrimp, Barnacles, Crab, Crayfish, and Lobster Almost all crustaceans are aquatic & have gills.
All have 2 pairs of antennae, three types of chewing appendages, and five pairs of legs.
Echinodermata: Starfish and Sea Urchins Belongs to a group of invertebrates that have tiny tube feet and body parts arranged around a central area.
A starfish has five arms and no head!
The hard, spiny covering of the starfish gives the animal protection.
A sea urchin belongs to this same group.
Its body is covered with spines.
Echinodermata… Radial symmetry Diets vary ~ predators, filter feeders, some eat rotting material Spiny skin covering an internal skeleton of plates Water-vascular system to help them move and eat Some can reproduce through regeneration from parts.