BIOL 1521 Lecture Notes - Lecture 7: Coevolution, Radula, Nematomorpha
Animal Evolution: Invertebrates
Phylum Porifera: sponges
• Similar to probable ancestor colonial protist leading to animals
• Cell specialization, but very loosely organized (lack true tissue level of organization)
• Very successful: about 10000 species with 50 freshwater species
Phylum Cnidaria
• Radial symmetry, diploblastic, incomplete gut
• Muscles and simple nerve net
• Specialized predators: delicate animals with a lethal sting (cnidocytes(
• Includes jellyfish, sea anemones, and corals
Phylum Ctenophora
• Biradial symmetry, complete digestive tract, two tentacles with sticky cells (colloblasts) for
entangling prey
• The "comb jellies" are named from the comb-like plates, or ctenes, arranged in 8 rows
along the body's surface
Phylum Platyhelminthes
• Flatworms
• Bilateral symmetry, triploblastic acoelomate animals; move via cilia on ventral surface
• Free living and parasitic forms
Phylum Rotifera (Rotatoria)
• Microscopic, pseudocoelomate
o Well developed body plan
• Interesting adaptations to life in ephemeral habitats
Spiralians: Worm-like critters
• Three major phyla out of many:
o Nemertea (ribbon worms)
o Annelida (segmented worms)
o Mollusca (lost segmentation, evolved shells)
Phylum Annelida
• Segmented worms, eucoelomate but coelom separated within each body segment
Phylum Mollusca
• Lost segmentation, but developed specialized body part (foot, mantle, shell, radula)
• Very successful
o Second only to arthropods for number of species
• Diversity of body forms in each class can be derived from a generalized hypothetical
ancestral body plan
Ecdysozoans
• Most numerous and successful group of animals on Earth
• Possess exoskeleton ranging from fairly flexible and thin cuticle to very thick, rigid "suit of
armor"
• Exoskeleton has multiple advantages:
o Protection
o Attachment point for muscles; mobility
o Barrier to external environment (improve homeostasis)
o Increased size/complexity of body plan
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