Intro to Animals
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Kingdom Animalia What are animals? • Animals eat to live: ‘ingestively’ heterotrophic • Multicellular • lack a cell wall Origins and Early Diversification of Animals • Sponges are the oldest known animals in the fossil record and are similar to protistan choanoflagellates. Choanoflagellate (a protist) Sponge (an animal) Water current out of sponge Choanoflagellate cell Food particles Water current Sponge feeding cell Interior of sponge Water current into sponge Origins and Early Diversification of Animals • There are about 35 Phyla in Kingdom Animalia • We’ll review approximately 14 of these • Four basic features vary in different animal body plans, and are the basis for grouping animals into different phyla: 1. Embryonic tissues 2. Body symmetry 3. Presence of a body cavity 4. Details of early development 1. Tissues • Tissue= highly organized and functionally integrated group of cells • All animals but sponges have tissues arranged in layers in their embryos No tissues Tissues present Parazoa (Phylum Porifera) Eumetazoa (all other phyla) 1. Tissues • In animals with embryonic tissues, the tissues are arranged in layers • Endodermdigestive tract, liver, lungs • Mesodermcirculatory system, muscles • Ectodermskin, nervous tissue • There may be 2 or 3 layers: • Diploblastic endo & ecto only • Triploblastic all 3 2. Symmetry • An animal’s body plan may have no symmetry (sponges), or show radial or bilateral symmetry Asymmetry Radial symmetry Bilateral symmetry Single plane of symmetry Anterior Posterior Multiple planes of symmetry (1. And 2.) Tissues and Symmetry • Animals that are diploblastic show radial symmetry • Animals that are triplobastic show bilateral symmetry No tissues Tissues present Parazoa (Phylum Porifera) Diploblastic, radial symmetry Eumetazoa Triploblastic, bilateral symmetry Radiata (Phylum Cnidaria & Ctenophora) Bilateria All other Phyla Significance of Tissues and Symmetry • Animals with bilateral symmetry are capable of unidirectional movement • Mesoderm made musculature possible • Together: directed movement and hunting 3. Fluid-filled body cavities • A coelom (body cavity) develops within mesoderm tissue in most triploblasts. • The coelom provides space in which organs can develop and acts as a hydrostatic skeleton in soft-bodied animals. • Some triploblasts have a pseudocoelom, which develops between mesoderm and endoderm and functions just as a coelom does. Body plans of the bilateria Hydrostatic skeleton of a nematode Muscle Gut Fluid-filled pseudocoelom Body wall Coordinated muscle contractions result in locomotion Muscles relaxed Muscles contracted Muscles contracted When the muscles on one side contract, the fluid-filled chamber does not compress. Instead, the animal bends. Muscles relaxed 3. Bilateria animals either have no coelom, pseudocoelom, or a true coelom No coelom Bilateria Pseudocoelom Phylum Platyhelminthes Phylum Rotifera Phylum Nematoda Coelom Coelomates: All other Phyla 4. Early events in embryogenesis • The last feature used to categorize animal body plans deals with details of the early development of animals • Animals develop from a single-celled zygote through a process called gastrulation Figure 32.1 Early embryonic development (Layer 1) Figure 32.1 Early embryonic development (Layer 2) Figure 32.1 Early embryonic development (Layer 3) Early events in embryogenesis • Among coelomates, there are 2 groups: • Protostomes: spiral cleavage, mouth develops first, coelom develops within blocks of mesoderm. • Deuterostomes: radial cleavage, mouth develops second, coelom develops from mesoderm cells that bud off the endoderm. Figure 32.7 A comparison of early development in protostomes and deuterostomes Odd group out • Three phyla of Coelomates have charateristics of both protostomes and deuterstomes • These are the Lophphorate Phyla Bilateria Spiral cleavage, mouth first, etc. lophophore Bilateria Radial cleaveage, mouth second, etc. Protostomia Phylum Mollusca Phylum Annelida Phylum Arthropoda Lophophorate Phylum Bryozoa Phylum Phoronids Phylum Brachiopoda Deuterostomia Phylum Echinodermata Phylum Chordata Molecular Systematics is moving some branches around on the phylogenetic tree of animals • Data based on nucleotide sequence of the small subunit ribosomal RNA (SSU-rRNA) • Early branches still the same • Deuterostomes still the same Animal phylogeny based on sequencing of SSU-rRNA Molecular Systematics is moving some branches around on the phylogenetic tree of animals • Differences: • Protostomes divided into 2 groups • Lophotrochozoaannelids,molluscs, lophophorates Trochophore larvae of annelids and molluscs • Ecdysozoanematodes, arthropods The Ecdysozoa are defined by molting Nematodes and arthropods shed their exoskeleton as they grow, a process called ecdysis Animal phylogeny based on sequencing of SSU-rRNA
