Animal Phylogeny 2025 PDF

Animal Diversity: Phylogenetic Relationships Introductory Biology II Spring 2025  Characteristics of the Animal Kingdom Animals are: multicellular, heterotrophic, eukaryotes that lack a cell wall. Ch. 32 Most animals possess tissues. A tissue is a group of cells arr...

Animal Diversity: Phylogenetic Relationships Introductory Biology II Spring 2025  Characteristics of the Animal Kingdom Animals are: multicellular, heterotrophic, eukaryotes that lack a cell wall. Ch. 32 Most animals possess tissues. A tissue is a group of cells arranged in a definite pattern or layer. Kidney tissue The cells in a tissue often perform a common function. Tissues come from embryonic layers called germ layers. Animals possess two unique tissue types: 1. nervous tissue neurons & supporting cells functions to conduct signals 2. muscle tissue functions in movement via contraction contraction results from the interaction of actin & myosin Animal Diversity How do scientists understand animal diversity? "Nothing in biology makes sense except in the light of evolution”.........Theodosius Dobzhansky phylogeny: classification scheme based on evolutionary relationships -hypothesis to explain available evidence -use evidence from many sources to construct a phylogeny Fig. 32.11 The animal kingdom is monophyletic which means derived from a single common ancestor. Ancestor believed to have been a unicellular protist. Level of Organization Animals are all multicellular and they are grouped in the metazoa. Metazoans are placed into 2 broad groups based upon the degree to which their cells are organized, i.e. whether or not true tissues are present.  Grade Parazoa grade Parazoa lack true tissues e.g. Phylum Porifera grade Eumetazoa true tissues are present  Symmetry - correspondence in size and shape of sides of the body when divided by a median plane Poriferans (sponges) are asymmetrical. In the rest of the animal kingdom, there are 2 major types of symmetry. radial symmetry bilateral symmetry  Radial Symmetry - more than 2 planes passing through the longitudinal axis divide the body into similar halves - body has one main axis around which the body parts are arranged  Bilateral Symmetry - animal can be divided into mirror-image right and left sides by a mid-sagittal plane  Bilateral Symmetry - bilateral animals often exhibit cephalization evolutionary trend towards concentrating nervous & sensory structures at the anterior end  No Symmetry Radiata Symmetry  Overview of Animal Development fertilization results in a diploid zygote - zygote undergoes numerous cell divisions called cleavages  Overview of Animal Development cont’d blastula stage at which the embryo is a hollow ball of cells  Overview of Animal Development cont’d gastrulation - formation of a layered embryo (gastrula) - may occur by invagination  Overview of Animal Development Gastrula stage embryo cont’d blastocoel archenteron blastopore Germ Layers in a Gastrula Stage Embryo ectoderm endoderm *mesoderm * a 3rd layer, mesoderm, forms between ectoderm & endoderm in many animals Animals that develop from embryos with 2 germ layers are called diploblastic. Those that develop from embryos with 3 germ layers are called triploblastic. Germ layers develop into specific adult tissues. In a triploblastic animal: ectoderm outer covering, nervous system endoderm gut, liver, lungs mesoderm muscle diploblastic cnidarians, ctenophores triploblastic platyhelminths,echinoderms, chordates, molluscs, arthropods, annelids Body Plans of the Bilateria  Acoelomate Body Plan region between gut & body wall is filled with tissue no body cavity eg. Phylum Platyhelminthes (flatworms) Pseudocoelomate (= blastocoelomate) body plan body cavity present, but not enclosed on all sides by tissue derived from mesoderm - eg. Phylum Nematoda (roundworms)  Coelomate Body Plan body cavity present and it is enclosed on all sides by tissue derived from mesoderm - eg. Phylum Annelida (segmented worms) Two Major Lineages of Animals Based on Development Developmental Protostome Deuterostome characteristic blastopore fate mouth anus cleavage spiral radial Blastopore Fate  Two Major Lineages of Animals Based on Development Developmental Protostome Deuterostome Characteristic blastopore fate mouth anus cleavage spiral radial Types of Cleavage radial cleavage deuterostomes spiral cleavage protostomes radial spiral Deuterostomes include echinoderms & chordates. Protostomes consist of 2 groups: Lophotrochozoa & Ecdysozoa These clades have been resolved mainly on the basis of molecular evidence. Ecdysozoans shed their exoskeleton in order to grow. This clade includes arthropods and nematodes (roundworms). Lophotrochozoans possess a lophophore and/or a trochophore larva. This clade includes ectoprocts, molluscs, and annelids.