Intro to invertebrates
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Intro to Invertebrates . Chapter 25 Sections 1 & 2. Invertebrates (inverts) include all animals that lack a backbone, or vertebral column. This includes 33 Phyla. Phylum Porifera. The term Porifera means “pore-bearers” in Latin. This phylum includes Sponges.

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Intro to Invertebrates

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Intro to Invertebrates

Chapter 25

Sections 1 & 2

  • Invertebrates (inverts) include all animals that lack a backbone, or vertebral column.

    • This includes 33 Phyla

Phylum Porifera

  • The term Poriferameans “pore-bearers” in Latin.

  • This phylum includes Sponges.

  • Most ancient member of the Kingdom Animalia.

  • One of the most simple organisms

Phylum Cnidaria

  • Organisms include jellyfish, anemones, hydra, and coral.

  • These organisms are always aquatic.

  • Can live in giant colonies such as the Great Barrier Reef

Phylum Nematoda

  • Range in size from microscopic to 1 meter

  • Can live on land and in water.

  • Some are parasitic

  • Closely related to the phylum Arthropoda


Phylum Platyhelminthes

  • Commonly known as flatworms.

  • They are the most simple animals to have 3 germ layers.

  • Most are only 3mm thick.


Phylum Annelida

  • Includes organisms such as earthworms and leeches

  • The word Annelida means little ring in Latin

Phylum Mollusca

  • Includes both marine and terrestrial organisms

  • Ex. Snails, clams, squid, and octopi

  • Have a larval stage in development

  • Typically have an internal or external shell



  • Echino- means spiny in Greek and Detmis- means skin (spiny skin)

  • Includes sea urchins, sand dollars, and Sea Stars

  • Only live in the sea

  • Have a structure called “tube feet”

Body Plans of Inverts

  • Body Symmetry

    • Radial Symmetry- a number of imaginary planes drawn through the center of the body will divide the organism in equal halves.

      • Ex: Sea Stars, Sea Anemone, and Jelly Fish

  • Bilateral symmetry- a single imaginary plane divides the body into left and right sides that are mirror images of each other.

    • Lobster, earthworms, snails

  • Germ Layers-during embryonic development the cells of most animals differentiate into 3 layers, called germ layers

    • Endoderm- is the inner most layer and develops the lining of the digestive tract and much of the respiratory system.

  • Mesoderm- middle layer that gives rise to muscles and much of the circulatory, reproductive, and excretory systems.

  • Ectoderm- outermost layer that produces sense organs, nerves, and the outer layer of the skin

  • Body Cavities- a fluid-filled space between the digestive tract and the body wall

    • The most complex organisms have a true coelom, which is a body cavity that develops within the mesoderm and is completely lined.

    • Pseudocoelom is a partially lined body cavity

    • Acoelomthere is no body cavity present.

  • Segmentation- repeated parts on an animal. Most have repeated body parts on the inside also.

  • Cephalization-The concentration of sense organs and nerve cells at the organisms anterior end. (to have a head)

    • The most successful animal groups exhibit cephalization.

Review Game

What type of symmetry?

What type of symmetry?

What type of symmetry?

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