Answers Chapter 27 Animal diversity phylogeny Study Q 1 How are animals different from other major eukaryotic groups plants fungi How are they similar In general animals are motile organisms with a gametic life cycle Individuals are diploid as juveniles and adults the haploid phase exists only as male and female gametes The female gamete or egg is larger and non motile The male gamete or sperm is smaller has a flagellum and is motile Animal cells lack a cell wall but possess an extracellular matrix consisting of a meshwork of proteins and polysaccharides In common with other eukaryotic groups animals are multicellular like Plants and Fungi and heterotrophic like Fungi 2 What are the three lines of evidence supporting the hypothesis that Choanoflagellates are sister to animals Choanoflagellate cells are morphologically indistinguishable from the collar cells choanocytes of sponges considered a basal group of animals collar cells have been identified in other animals cnidarians flatworms and echinoderms but never in other major protist groups or plants or fungi DNA sequence data link choanoflagellates and animals and choanoflagellates possess genes for signaling and adhesion proteins known only in animals 3 According to your textbook why are the sponges porifera considered basal animals Sponges lack both body symmetry and true tissues derived from germ layers among other cell types sponges possess choanocytes collar cells which resemble the cells of choanoflagellates with which they share DNA sequences specific to animals These lines of evidence suggest that animals evolved from a choanoflagellate like animal 4 Put the following milestones in animal evolution in chronological order from oldest to most recent origin of mammals Cambrian explosion Edicaran fauna extinction of large non flying dinosaurs rise of large mammals vertebrate transition to land diversification of flowering plants and insects Ediacaran fauna Cambrian explosion vertebrate transition to land origin of mammals diversification of flowering plants and insects extinction of large non flying dinosaurs rise of large mammals 5 How is cephalization an adaptive feature for bilaterally symmetric motile animals Cephalization is associated with the concentration of nervous tissue ganglion or brain and sensory organs at the anterior part of the body The brain integrates incoming sensory information this is adaptive to organisms with bilateral symmetry that meet their environment with the anterior end of their bodies first usually as they are moving through it 6 How does the radial symmetry of a jellyfish and a sea anemone fit their lifestyle Jellyfish are planktonic organisms that is they float in their environment which meets their bodies from all directions at the same time This is also true of the sessile sea anemones although they do not float It would be of no advantage for these organisms to have a concentration of particular organs such as a brain and sensory organs at one end of their bodies 7 Name the derivative organ systems of each germ layer ectoderm mesoderm and endoderm Ectoderm skin and nervous system Mesoderm skeletal muscular systems some glands of the digestive system Endoderm lining of the lumen of the digestive tract the liver and the lungs 8 What is the function of the body cavity or coelom How is this different from the lumen of the digestive tract of a human The coelom is a fluid filled cavity that provides a space for the internal organs of an organism to grow and move independently of the rest of the body In humans the coelom is the interior space between the body wall and the outer wall of the digestive tract and it is completely lined with tissues derived from mesoderm The lumen of the digestive tract of humans is the long cavity within the digestive tract itself and is technically considered outside the body 9 What is the difference between the metazoa and the eumetazoa Metazoa are animals that are multicellular eukaryotes that do not have germ layers e g phylum porifera sponges Eumetazoa are multicellular animals that have at least two germ layers endoderm and ectoderm e g phylum cnidaria and arthropoda 10 What feature links the arthropoda and nematoda and places both phyla in the ecdysozoa Molecular data place these phyla in the same larger clade ecdysozoa as well as the physiological feature known as ecdysis or molting 11 Explain how sponges feed Sponges feed by filtering water containing small animals protists detritus through the pores in their body wall towards the central cavity or spongocoel currents directed into the sponge through the pores are created by the flagella of choanocytes The choanocytes draw particles within their collar of finger like projections which are then phagocytized The particles are digested intracellularly or transferred to amoebocytes for delivery of nutrients to other parts of the animal 12 Describe three adaptations that have enabled insects to thrive on land Insects are well adapted to a terrestrial environment because they have an exoskeleton which helps minimize water loss tracheae that permit gas exchange with minimal water loss and wings that provide many advantages without sacrificing a pair of legs 13 Is the apparent radial symmetry of the echinodermata homologous or analogous to the radial symmetry of the cnidaria The apparent radial symmetry of echinoderms is analogous to the radial symmetry of the cnidaria which means that this type of body symmetry evolved independently within these two groups and not from a common ancestor 14 When was the Cambrian explosion State the current hypotheses put forward to explain this phenomenon The Cambrian explosion took place between 535 and 525 million years ago and is evidenced by an extraordinary number and diversity of larger animal fossils in rocks of that age The three hypotheses to explain this are a dramatic increase in atmospheric oxygen 3 12 evolving predator prey interactions and duplication and changes in the Hox genes genes that control development in many organisms 15 Identify four derived characters that all chordates have at some point during their life All chordates have a dorsal hollow nerve cord a notochord pharyngeal clefts and a post anal tail at some point in their lives 16 Explain how humans can be chordates yet lack most of the main derived characters of chordates as adults Humans display all four features characteristic of chordates during their embryonic phase 17 What characteristics do