Survey of the Invertebrates

Kingdom Animalia Animalia: The Cambrian Explosion Number of organisms in the fossil record is increasing New groups were evolving fast Bodies were larger Skeletons and hard parts like shells

Animalia Specialized cells also appeared Different groups of cells became specialized As animals evolved they became more complex Specialized cells organized into tissues Tissues organized to form organs Organs evolved into organ systems

Animalia: Invertebrates Animals without a backbone Many, many invertebrate phyla Three trends in Invertebrate evolution Germ layers, Coelom, Segmentation

Invertebrates: Three germ layers Common ancestors of multicellular animals evolved two distinct cell layers: an ectoderm layer (outside) and an endoderm layer (inside) Sponges and some jellyfish have these two only Other jellyfish and all other animals have a middle layer, mesoderm, that develops into muscles and skeletons

Invertebrates: Coelom The existence of a mesoderm lined cavity inside the body. This is space for organs to grow without being affected by the movement of the body

Invertebrates: segmentation Invertebrates: Body plan built from segmentation Body is compartmentalized in segments Allow increases in size with minimal new genetic information (just repeat what you have) Segments can be specialized for specific functions Look at the diagrams on page 447

Invertebrates: Body plan symmetry Look at the diagrams on page 448 Some invertebrates have no symmetry Some have radial symmetry (body parts repeat around an imaginary line drawn through the center of the body) Some have bilateral symmetry (animals have identical right and left sides, fronts and backs, upper and lower sides)

Invertebrates: Habitats Life in fresh water, salt water and on land; Some live part of their life in water another part on land and vice versa

Survey: 9 phyla of invertebrates Porifera (sponges) Simplest of all invertebrates; no symmetry Cnidaria (jellyfish, sea anemones, hydra) Mostly salt water, some fresh water, radial symmetry Platyhelminthes (flatworms) Simplest animal with bilateral symmetry Many are parasites Nematoda (roundworms) Fist to show a tube like digestive system Range in size from microscopic to more than a meter long

Survey: 9 phyla of invertebrates Mollusca (mollusks, clams, snails, squids) Most are salt water, some fresh water Most have shells; octopus (8 tentacles) and squids (10 tentacles) have no shells Annelida (segmented worms, earthworms) Live on land and in water Echinodermata (star fish, sea cucumbers, sea urchins) Show five-part radial symmetry Arthropoda (spiders, crustaceans, insects) THE most successful of all the animals Jointed appendages and exoskeleton Lobsters, shrimps and crabs, spiders, insects Invertebrate chordates (sea squirts) Link between invertebrates and vertebrates Endoskeleton with a notochord