Trends in Animal Evolution

Possible ancestral organism - choanoflagellates Image, The colonial flagellate hypothesis for origin of animals - Image Timeline of the evolutionary history of animals Fig 26.1

Characteristics of animals

• multicellular, heterotrophic eukaryotes
• ingest food
• no cell walls
• unique tissues, nervous and muscular, allow for movement and response
• most reproduce sexually
• development: zygote to blastula to gastrula, Image
• some have immature stage called a larva which goes through metamorphosis to become an adult

Traditional phylogeny of animals - Fig. 25.1 - Animal phylogeny based on molecular sequencing - Fig. 25.2

Evolutionary trends among the animals Fig 25.3

Major animal phyla Table 25.2a, b, c, d. Animal diversity.

The Parazoa - no true tissues

Phylum Porifera: The Sponges - Fig 25.5, Image and Fig 25.4

Symmetry - Fig. 25.10

Radial symmetry

Bilateral symmetry

The Eumetazoa - true tissues develop from germ layers

Diploblastic (2 Cell Layers - Image) Eumetazoa - The Radiata

Phylum Cnidaria: The Cnidarians - Image and Fig 25.7and Fig 25.6

Polyp vs. medusa - Image swimming jellyfish, a medusa. Fig. 25.8

Digestion - Image Hydra eating water flea!

Triploblastic Eumetazoa - The Bilateria

Body Plans of Triploblastic Bilaterally Symmetrical Animals - Fig. 25.16

Acoelomate

Pseudocoelomate

Coelomate

Protostomia vs. Deuterostomia - Image and Fig. 25.34

Protostomia

Phylum Platyhelminthes: The Flatworms Fig 25.12 and Fig. 25.11

Acoelomate animals - no body cavity

Planarians - Fig. 25.15

Flukes - Schistosoma blood flukes. Life cycle - Image and the human liver fluke Fig 25.13

Tapeworms - Fig. 25.14 and image, image2, and pets and tapeworms.

Phylum Nematoda Fig 25.18: Nematodes Image and roundworms. Image - parasitic Trichinella

Pseudocoelomate animals: a false coelom (body cavity)

Phylum Mollusca: The Mollusks Basic Body Plan

Coelomate animals - Fig 25.19 and Fig 25.20; snails, slugs - Image; nudibranch, the movie!; bivalves - Image; octopuses, squids - Image

Phylum Annelida: The annelids Fig. 25.21: Segmented worms - Image and - earthworms - internal anatomy - Fig 25.22, leeches, polychaetes

Phylum Arthropoda (Jointed-foot animals) Fig. 25.23 and Fig 25.25

Coelomate animals with exoskeletons. Mouthparts Fig 25.26 and Fig. 25.32

Crustaceans (Fig 25.29 and Image) like lobsters (external anatomy - Image) Lobster mouthparts in action! crabs, shrimp. Horseshoe crabs (Image). Arachnids like spiders (Fig. 25.28 and Image), scorpions, ticks and mites (Image). Millipedes and centipedes (Fig 25.31). Insects Fig 25.33

Deuterostomia - Coelomate animals

Phylum Echinodermata: (Image and Fig 25.35) The echinoderms - starfish (Fig 25.36), sea cucumbers, sea urchins. Tube feet - the movie!

Phylum Chordata: non-vertebrate and vertebrate chordates. Covered in next lecture.