INVERTEBRATE COMPARATIVE ANATOMY

Invertebrates make up 95% of the animal world. While there is a lot of variation among invertebrates, all of them lack a vertebral column.

1. Taxonomy a. Domain Eukarya i. Kingdom Animalia

2. Invert Phyla (most primative to advanced) a. Phylum Porifera - Sponges. Sessile filter feeders, no tissues or organs, asymmetrical. Sponges are classified as animals because they lack cell walls and are heterotrophs

b. Cnidaria Corals, jellyfish and anemones. Stinging cells, simplest animals with symmetry.

c. Phylum Platyhelmenthes Flatworms. Soft bodied worms that have tissues and internal organ systems, bilateral symmetry and cephalization. Many are parasitic, including flukes and tapeworms.

Platyhelmenthes Liver fluketapeworm

d. Phylum Nematoda Roundworms. Unsegmented worms with a two opening digestive tract. Many are parasitic, including Trichnids, Filarial worms, and Ascarids,

Nematodes

e. Phylum Annelida segmented worms with a true coelom. Includes leeches and earthworms.

Annelids Giant Australian EarthwormLeech

f. Phylum Mollusca Soft bodied animals that have a mantle (foot)and usually a shell. Some have a high degree of cephalization, cephalopods have closed circulatory systems (the others have an open circulatory system). Mollusks include snails, clams, oysters, squid and octopus

g. Phylum Arthropoda Largest of all phyla. Segmented bodies, exoskeleton and jointed appendages. Three main classes of arthropods include: i. Crustaceans – aquatic arthropods including crabs, lobster, shrimp ii. Arachnids – spiders, scorpions, ticks, etc. iii. Insects – 6 legged, 3 segments “bugs”

Arthropods crustaceansarachnids

h. Echinodermata Spiny skin, endoskeleton, water vascular system and tube feet. Most exhibit radial symmetry. Includes: starfish, sea urchins, sand dollars and sea cucumbers