Each animal phylum has a unique body plan. Vertebrates have an internal segmented backbone. Invertebrates do not have a backbone. Invertebrates encompass most animal groups.

Three criteria are used to categorize animals Protostomes Deuterostomes Body plan symmetry Bilateral: body divides equally along one plane (mirror images) Radial: body arranged in a circle around a central axis Tissue layers Bilateral have 3 distinct layers Radial have 2 distinct layers Developmental patterns Protostomes: mouth first, anus second Deuterostomes: anus first, mouth second

Protostomes and deuterostomes are the two major radiations on the animal phylogenetic tree. Based on anatomical and molecular evidence Porifera Cnidaria Platyhelminthes Annelida Mollusca Nematoda Arthropoda Echinodermata Chordata RADIAL NO TISSUES PROTOSTOMES DEUTEROSTOMES jellyfish, coral, anemones sponges flatworms Segmented worms clams, snails, octopuses roundworms insects, spiders crustaceans, sea urchins sea stars, vertebrates lancelets,

Porifera AKA: Sponges Most primitive animals 570 myo, >9000 species Specialized cells, but no true tissue Closely related to protists Neither protistomes or deuterostomes

Shared characteristics Sessile Filter feeders Specialized cells include: Spicule: skeletal like cells; spongin, silica, or CaCO3 Pinacocytes: outer layer Choanocytes: inner layer, each has a flagellum Amoebocytes: middle layer, absorb and digest

Sponge Reproduction Reproduce sexually or asexually Sexual Asexual Hermaphrodites, producing eggs/sperm at different times Sperm is released, captured by female of same species Ciliated larvae form from zygote Asexual Budding: small piece breaks off, but can still survive

Cnidaria AKA: Stinging nettles Nematocyst: capsule with a poison barb at one end > 9000 aquatic species Mobile Two body forms Polyp Medusa Gastrovascular cavity

Cnidarian Reproduction Sexually: mostly medusa- Gametes released in water Zygote develops into free-swimming larva, called planula Asexually: mostly polyps-budding

The four major cnidarian classes are defined by their dominant body form. Anthozoans such as sea anemones have a dominant polyp stage. Hydrozoans such as hydra alternate between forms. Scyphozoans are jellyfish with a dominant medusa form. Cubozoans such as sea wasps have a dominant medusa form.