Who is in the Kingdom Animalia? Let’s create an Animal list…

Characteristics Multicellular heterotroph Lack cell walls Most have nerves, muscles, capacity to move at some point in the life cycle Ability to reproduce sexually Specialized sensory structures and nervous system Cells exist in extensive extracellular matrix Unique cell junctions

Traditional classifications Most biologists agree kingdom is monophyletic Animal genomes are very similar Most likely ancestor a colonial flagellated protist similar to choanoflagellates About 35 recognized animal phyla

Who are the animal phyla?

Traditional classification based on body plans 4 main morphological and developmental features used Tissue types Symmetry type Body cavity Embryonic development

Tissues Metazoa divided into Parazoa (no specialized tissues or organs) and Eumetazoa (more than one type of tissue and organs)

Symmetry Eumetazoa are radially symmetrical (Radiata) or bilaterally symmetrical (Bilateria) Bilateral animals have cephalization and dorsal and ventral surfaces Radial animals have oral and aboral sides

J.B.S. Haldane The Creator would appear as endowed with a passion for stars, on the one hand, and for beetles on the other, for the simple reason that there are nearly 300,000 species of beetle known, and perhaps more, as compared with somewhat less than 9,000 species of birds and a little over 10,000 species of mammals. Beetles are actually more numerous than the species of any other insect order. That kind of thing is characteristic of nature.

http://www.youtube.com/watch?v=UgT5rUQ9EmQ

Number of cell layers Radial animals have 2 embryonic cell layers Diploblastic Bilateral animals have 3 germ layers Triploblastic Cell layers develop during gastrulation Inner layer – endoderm Outer layer – ectoderm Mesoderm - 3rd layer in bilateral animals Forms muscles and most other organs http://www.youtube.com/watch?v=8v6cXkzlEQA

Body cavity True coelom – body cavity is completely lined with mesoderm (coelomates) Pseudocoelom – coelom is not completely lined by tissue derived from mesoderm (pseudocoelomates) Acoelomates – lack a body cavity entirely Fluid-filled body cavity can protect internal organs or be used as hydrostatic skeleton

Embryonic development Which is which (usually)?!? Spiral cleavage Schizocoelous coelom development Blastopore becomes anus Cleavage is indeterminate- pluripotent stem cells Radial cleavage Enterocoleus coleom development Blastopore becomes mouth Cleavage determinate

Other methods of classification Possession of exoskeleton Development of notochord Presence or absence of metamerism (segmentation) Traced to changes in Hox genes

Molecular views of animal diversity Molecular techniques used to classify animals by comparing similarities in the DNA and the ribosomal RNA of animals, especially sequences of nucleotides in the gene that encodes RNA of the small ribosomal subunit (SSU rRNA) Advantage generally more objective and subject to more rigorous testing

Similarities between traditional and molecular phylogeny The clade called Metazoa is monophyletic, meaning all animals came from a single common ancestor. At the earliest stages of evolution, molecular phylogeny supports the traditional view of the split between Parazoa and Eumetazoa. There is also agreement about an early split between Radiata and Bilateria, with most animal phyla belonging to the Bilateria. Molecular phylogeny also agrees that the echinoderms and chordates belong to a clade called the Deuterostomia.

2 key differences between traditional and molecular phylogeny Division of protostomes into 2 clades Traditionally split into Deuterostomia and Protostomia based on embryonic development Deuterostomes still separate but protostomes divided into Lophotrochozoa and Ecdysozoa Presence or absence of a body cavity Traditionally split into coelomates, pseudocoelomates and acoelomates Molecular evidence indicates presence or absence not a useful characteristic