HOW DO WE CLASSIFY INVERTEBRATE ANIMALS?

Animals that don´t have a spinal cord are called invertebrates. Invertebrate animals are classified into six groups: arthropods, molluscs, porifera, coelenterates, echinoderms and annelids.

Molluscs. These invertebrates have soft bodies, and most also have a hard shell. They absorb oxygen through gills, and reproduce by laying eggs.

Coelenterates. These animals have a soft body. Some have long tentacles. They absorb oxygen through their skin. They reproduce by growing a bud, or small body part. Eventually the bud breaks off and grows into a new organism.

Jellyfish are coelenterates. Photo from flickr by NBPhotostream

Porifera (or sponges). These invertebrates have a soft body with holes called pores. They absorb oxygen and nutrients through the pores. They reproduce by forming buds.

By Nhobgood Nick Hobgood (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Echinoderms. These animals have bodies covered with sharp spikes. Some also have arms and tentacles. Some echinoderms have gills, others absorb oxygen through their skin. Echinoderms are oviparous.

Photo from wikimedia.

Arthropods. These invertebrates have an exoskeleton and jointed legs that bend. Some arthropods have simple lungs. Others absorb oxygen through their gills. Arthropods are oviparous.

Annelids. These animals have a long, soft body that is divided into rings called segments. Some annelids absorb oxygen through their skin, but other have gills. Annelids can reproduce by budding, but some are oviparous.

Shells, exoskeletons and soft bodies with no protective body covering are the three types of body coverings found in invertebrates. Each one is typical of a specific type of invertebrate.