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. Water current Food particles Choanoflagellate (a protist) Sponge feeding cell Water current into sponge Interior of sponge Water current out of sponge Sponge (an animal) Choanoflagellate cell

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 Endoderm  digestive tract, liver, lungs Mesoderm  circulatory system, muscles Ectoderm  skin, 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 Multiple planes of symmetry Radial symmetry Asymmetry Posterior Ventral Dorsal Single plane of symmetry Anterior Bilateral 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) Eumetazoa Diploblastic, radial symmetry 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

Gut Muscle Fluid-filled pseudocoelom Body wall Hydrostatic skeleton of a nematode

When the muscles on one side contract, the fluid-filled chamber does not compress. Instead, the animal bends. Muscles contracted Muscles relaxed Muscles contracted Muscles relaxed Coordinated muscle contractions result in locomotion

3. Bilateria animals either have no coelom, pseudocoelom, or a true coelom Phylum Platyhelminthes Bilateria No coelom Pseudocoelom Phylum Rotifera Coelomates: All other Phyla Coelom Phylum Nematoda

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 Protostomia Phylum Mollusca Phylum Annelida Phylum Arthropoda Bilateria lophophore Lophophorate Phylum Bryozoa Phylum Phoronids Phylum Brachiopoda Radial cleaveage, mouth second, etc. Spiral cleavage, mouth first, etc. 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 Lophotrochozoa  annelids,molluscs, lophophorates Ecdysozoa  nematodes, arthropods 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

Animal phylogeny based on sequencing of SSU-rRNA