An Introduction to Animals

Chapter 30 Opening Roadmap. © 2017 Pearson Education, Inc.

What Is an Animal? Animals are eukaryotes that share key traits: Multicellularity, with cells that Lack cell walls Have an extensive extracellular matrix Heterotrophy They obtain necessary carbon compounds from other organisms Most ingest their food rather than absorbing it Motility They move under their own power at some point in their life cycle

Protists in an older taxonomic “kingdom” Figure 30.1 Bacteria Archaea About 3.5 billion years ago!! Amoebozoa OPISTHOKONTA Sister Kingdom to Animalia Fungi Choanoflagellates From flagellated protists Animals Only 0.5 million years ago! EUKARYOTES Excavata Algae Figure 30.1 Choanoflagellates Are the Closest Living Relatives to Animals. Land plants Rhizaria Protists in an older taxonomic “kingdom” Alveolata Stramenopila © 2017 Pearson Education, Inc.

These have more or less radial symmetry Table 30.1-1 Biologists have described about 1.5 million species in 30–35 phyla (major lineages) of animals—the exact number is estimated to be much larger. These have more or less radial symmetry These develop their embryonic mouth before their anus Table 30.1-1 An Overview of Major Animal Phyla. © 2017 Pearson Education, Inc.

Largest phylum! More than all the other animals combined! Table 30.1-2 Largest phylum! More than all the other animals combined! These develop their embryonic mouth after their anus, i.e. second! Table 30.1-2 An Overview of Major Animal Phyla. © 2017 Pearson Education, Inc.

What Key Innovations Occurred during the Origin of Animal Phyla? Biologists consider several types of data: Fossils Comparative morphology Comparative development (evolutionary developmental biology, or evo-devo) Comparative genomics

Animalia is a clade (monophyletic), a natural (legitimate) taxon Figure 30.2 Choanoflagellates ANIMALIA Fungi Porifera Choanoflagellates (sponges) ANIMALIA Here we are seeing the kingdom divided into some of the 30-some phyla (major groupings) Multicellularity Ctenophora (comb jellies) Cnidaria (jellyfish, corals, sea anemones) LOPHOTROCHOZOA Diploblasty Rotifera (rotifers) Loss of coelom Animalia is a clade (monophyletic), a natural (legitimate) taxon Platyhelminthes (flatworms) Segmentation Annelida (segmented worms) PROTOSTOMES Mollusca BILATERIA (snails, clams, squid) Figure 30.2 A Phylogeny of Major Animal Phyla Based on DNA Sequence Data. ECDYSOZOA Nematoda (roundworms) Bilateral symmetry Triploblasty Cephalization Coelom? Arthropoda Segmentation (insects, spiders, crustaceans) DEUTEROSTOMES DEUTEROSTOMES Radial symmetry Echinodermata (in adults) (sea stars, sand dollars) Chordata Segmentation (vertebrates, tunicates) © 2017 Pearson Education, Inc.

Morphological Evidence for the Sponges-First Hypothesis Sponges share characteristics with choanoflagellates Both are benthic (live at bottom of aquatic environments) Both are sessile (adults live permanently attached to a substrate rather than moving freely) Both feed using cells with nearly identical morphology Beating flagella of choanoflagellates and specialized cells in sponges called choanocytes trap organic debris Feeding occurs at the cellular level

Sponges share characteristics with choanoflagellates Figure 30.3 Sponges share characteristics with choanoflagellates (a) Choanoflagellates are sessile protists; some are colonial. (b) Sponges are multicellular, sessile animals. Colony Multicellular organism (cross section) Choanoflagellate cell Water current Food particles Water current Sponge feeding cell (choanocyte) flagellum microvilli (collar) Figure 30.3 Choanoflagellates and Sponge Feeding Cells Are Almost Identical in Structure and Function. Both are benthic Both are sessile Both feed using cells with nearly identical morphology © 2017 Pearson Education, Inc.

ctenophores, sponges, cnidarians Figure 30.5 Symmetry in animals evolved over time (a) Radial symmetry (b) Bilateral symmetry Figure 30.5 Body Symmetry. ctenophores, sponges, cnidarians the rest of Animalia © 2017 Pearson Education, Inc.

The defining feature of Kingdom Animalia is ? Figure 30.8 (a) Nerve net: diffuse neurons in hydra (b) Central nervous system: clustered neurons in earthworm Cerebral ganglion (brain) Ganglia Cephalization eventually led to a central nerve system for sensing the enviornment and controlling movement and other responses. Figure 30.8 Associations between Body Symmetry and the Nervous System. The defining feature of Kingdom Animalia is ? © 2017 Pearson Education, Inc.

The embryo of animals evolved three-embryonic layers Figure 30.9 The embryo of animals evolved three-embryonic layers And a body cavity (coelom) inside Skin and nervous system derived from ectoderm Muscles and organs derived from mesoderm Coelom (cavity lined with mesoderm) Mouth Gut derived from endoderm In protostomes, the mouth (stoma) develops first (proto-) Figure 30.9 The Tube-within-a-Tube Body Plan Is Common in Animals. Anus In deuterostomes, the mouth (stoma) develops second (deutero-) © 2017 Pearson Education, Inc.