Invertebrates

The majority of animals on this planet are invertebrates 32 of the 34 phyla of animals are invertebrates Invertebrates lack a true defined backbone

Characteristics of Animals Symmetry - is the balanced distribution of duplicate body parts or shapes. The body plans of most multicellular organisms exhibit some form of symmetry, either radial symmetry or bilateral symmetry. A small minority exhibit no symmetry (are asymmetric). Body Cavity - (coelom) The cavity within the body of all animals higher than the coelenterates and certain primitive worms Digestion Reproduction

Phylum Porifera Sponges – approx 5000 species Aquatic organisms, usually marine Usually irregularly shaped – asymmetrical ( no plane of division) Filter feeders – no true digestive system Reproduction is asexual (budding) and sexual Sexual fertilization is external - hermaphrodites No true body cavity

Phylum Cnidaria Characterized by bodies that are radial symmetrical Aquatic organisms – mostly marine Bodies have a opening that has tentacles around it Digestion occurs in the opening by secreting digestive juices into the cavity and absorbing the nutrients Reproduction is both sexual and asexual - hermaphrodites There is an opening but no body cavity Sexual fertilization is external

The two different forms of a Cnidarian body

Phylum Platyhelminthes Flatworms – they have bilateral symmetry and show signs of cephalization (head) They have body tissues but do not have a true body cavity Single opening through which food enters and waste exits - digestion is extracelluar Asexual and sexual reproduction Fertilization is internal – hermaphrodites

Phylum Nematoda Roundworms – they have bilateral symmetry They have three layers of tissue and have a pseudocoelom (tube within a tube) Does not have a well developed digestive system One way – two openings Sexual reproduction – internal fertilization Hermaphrodites and separate sexes

Phylum Arthropoda Bilateral symmetry There is the presence of a true body cavity Digestion is in a tube with two openings and one direction Reproduction is sexual – with internal fertilization Separate sexes with a few hermaphrodites

Scientists have identified over 1 million species Predict that there are over 10 million species Extremely diverse, thus, they can be found virtually anywhere

Why are arthropods so successful? Rigid, jointed external skeleton (exoskeleton) Water proof protective armour Site for muscle attachment Protects against water loss Specialized nature of body segments Head Thorax Abdomen Well developed nervous system Coordinate body movement Diversity of structures and functions for obtaining nutrition Utilize plant and animal sources