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What are animals? Animals eat to live: ‘ingestively’ heterotrophic Multicellular lack a cell wall. Kingdom Animalia. Sponges are the oldest known animals in the fossil record and are similar to protistan choanoflagellates. Origins and Early Diversification of Animals. Sponge (an animal).
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What are animals? Animals eat to live: ‘ingestively’ heterotrophic Multicellular lack a cell wall Kingdom Animalia
Sponges are the oldest known animals in the fossil record and are similar to protistan choanoflagellates. Origins and Early Diversification of Animals Sponge (an animal) Choanoflagellate (a protist) Water current out of sponge Choanoflagellate cell Sponge feeding cell Interior of sponge Food particles Water current into sponge Water current
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 Origins and Early Diversification of Animals
Tissue= highly organized and functionally integrated group of cells All animals but sponges have tissues arranged in layers in their embryos 1. Tissues Parazoa (Phylum Porifera) No tissues Tissues present Eumetazoa (all other phyla)
In animals with embryonic tissues, the tissues are arranged in layers Endodermdigestive tract, liver, lungs Mesodermcirculatory system, muscles Ectodermskin, nervous tissue 1. Tissues • There may be 2 or 3 layers: • Diploblastic endo & ecto only • Triploblastic all 3
An animal’s body plan may have no symmetry (sponges), or show radial or bilateral symmetry 2. Symmetry Asymmetry Radial symmetry Multiple planes of symmetry Posterior Single plane of symmetry Dorsal Bilateral symmetry Anterior Ventral
Animals that are diploblastic show radial symmetry Animals that are triplobastic show bilateral symmetry (1. And 2.) Tissues and Symmetry Parazoa (Phylum Porifera) No tissues Diploblastic, radial symmetry Radiata (Phylum Cnidaria & Ctenophora) Tissues present Eumetazoa Triploblastic, bilateral symmetry Bilateria All other Phyla
Animals with bilateral symmetry are capable of unidirectional movement Mesoderm made musculature possible Together: directed movement and hunting Significance of Tissues and Symmetry
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. 3. Fluid-filled body cavities
Hydrostatic skeleton of a nematode Muscle Fluid-filled pseudocoelom Gut 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 Phylum Platyhelminthes No coelom Phylum Nematoda Phylum Rotifera Pseudocoelom Bilateria Coelom Coelomates: All other Phyla
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 4. 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. Early events in embryogenesis
Figure 32.7 A comparison of early development in protostomes and deuterostomes
Three phyla of Coelomates have charateristics of both protostomes and deuterstomes These are the Lophphorate Phyla Odd group out
Bilateria Protostomia Phylum Mollusca Phylum Annelida Phylum Arthropoda Spiral cleavage, mouth first, etc. Lophophorate Phylum Bryozoa Phylum Phoronids Phylum Brachiopoda lophophore Bilateria Radial cleaveage, mouth second, etc. Deuterostomia Phylum Echinodermata Phylum Chordata
Data based on nucleotide sequence of the small subunit ribosomal RNA (SSU-rRNA) Early branches still the same Deuterostomes still the same Molecular Systematics is moving some branches around on the phylogenetic tree of animals
Differences: Protostomes divided into 2 groups Lophotrochozoaannelids,molluscs, lophophorates Ecdysozoanematodes, arthropods Molecular Systematics is moving some branches around on the phylogenetic tree of animals Trochophore larvae of annelids and molluscs
The Ecdysozoa are defined by molting Nematodes and arthropods shed their exoskeleton as they grow, a process called ecdysis