Chapter 33 Invertebrates Figure 32 11 o Most recent hypothesis about animal phylogeny o Diploblastic 2 tissue layers endodermic and ectodermic o Triploblastic 3 tissue layers o The development of multiple tissue layers helped with the development of life forms Concept 33 1 Sponges are basal animals that lack true tissues Porifera Phyla Calcarea and Silicea o Live in both fresh and marine waters o Lack true tissues and organs o Asymmetrical body Sponges Figure 33 4 Sponges are suspension feeders feed on particles that float throughout the water o Filter water passing through their bodies o Pores doughnut shaped cells that span the body wall o Choanocytes like the spongocoet movement of flagella sets up water flow trap food and ingest it by phagocytosis pass it along to amoebocytes o Amoebocytes transport nutrients to other cells secretes spicules o Mesohyl gelatinous layer within the sponge contains amoebocytes Clicker Q Water movement through a sponge would follow what path o A Pore spongocoel osculum Sponges are considered basal animals Concept 33 2 Cnidarians are an ancient phylum of eumetazoans Cnidarians A wide range of sessile planted on the ground and floating forms including jellyfish corals and hydras Simple diploblastic radial body plan o Body plan is a sac with a central gastrovascular cavity o Single opening serves as both mouth and anus o Mesoglea layer between epidermis and endodermis gastrodermis the jelly part of the jellyfish Cnidarian Body Plans bell Figure 33 5 form Asymmetrical o Radial symmetry when you draw a plane through an animal and you o Bilateral symmetry you can only divide something one way for it to still have symmetry remain symmetrical Zygote 8 cell stage blastula gastrulation gastrula endoderm and ectoderm Polyp form is generally sessile Medusa form moves freely in water by passive drifting and contractions of 9 o A lot of cnidarians cans witch from the sessile form to the medusa o Gastrovascular cavity gastrodermis mesoglea epidermis Defining Feature of Cnidarians Cnidocytes unique cells that function in defense and the capture of prey Stimulus causes the cell to evert releasing thread Some cnidocytes sting others just entangle prey Figure 33 6 Cnidarian Diversity Figure 33 7 Clicker Q Which of the following animals is responsible for more lethal attacks on humans each year o A Cubozoans Clicker Q How many planes through the central axis will divide an organism with radial symmetry into roughly equal halves o A Many Concept 33 3 Lophotrochozoans a clade identified by molecular data have the widest range on animal body forms Figure 33 2 o Bilateria show cephalization and 3 tissue layers Once you have three tissue layers there is the development of an inner body cavity a coelom Acoelomate basic 3 tissue layer animals Flatworms Phylum Platyhelminthes Triploblastic development but acoelomate Table 33 2 Endoderm mesoderm middle tissue layer exoderm Class Turbellaria Free living flatworms Have Figure 33 9 Figure 33 10 Class Trematoda parasitic o Light sensitive eyespots o Centralized nerve net with anterior ganglia o Gastrovascular cavity with 2 way pharynx Figure 33 11 specialized life cycle that involve multiple hosts Have adult male and female flatworms within a host body Reproduce in the host body and leave the host by feces and water Larvae penetrates host skin Scolex attaches to the host Tapeworms parasitic Class Cestoda Proglottids are the reproductive structures Break off after fertilization Don t have a mouth absorb nutrients from the host s intestines Figure 33 12 Rotifers Phylum Rotifera Alimentary canal with separate mouth and anus this is the point in animal evolution where there is a mouth and anus Pseudocoelomate methoderm layer is only attached to the tissue layer Reproduce by parthenogenesis females release eggs that don t need to be fertilized Figure 33 13 Clicker Q In the life cycle of a typical hydrozoan Class Hydrozoa which of the following would most likely be free swimming o A Medusa Phylum Mollusca Figure 33 15 Class Polyplacophora Also known as Chitons o Most molluscs have an open circulatory system Heart pumps hemolymph through arteries and into sinuses o Radula rasp like feeding organ scraps and scoops food items Class Gastropoda Snails and slugs Asymmetrical body usually with a coiled shell o Result of torsion rotation of the visceral mass main body mass in some species it twists 90 degrees and in others it twists 180 degrees allows creatures to move into their shell for protection Shell has 8 plates Foot used for locomotion Radula No true head Figure 33 16 Foot for locomotion Radula Class Bivalvia Clams mussels scallops oysters Flattened shell with 2 valves Head reduced Paired gills No radula Mostly suspension feeders Figure 33 19 and Figure 33 20 Class Cephalopoda Squids octopods cuttlefish chambered nautili Head surrounded by grasping tentacles o Usually with suckers Shell may be external internal or absent Figure 33 21 Clicker Q Which of the following combinations of phyla and characteristics is o A Porifera gastrovascular cavity two tissue layers incorrect Phylum Annelida Annelids are also coelomate segmented into rings Anatomy of an Annelid e g Earthworm Body is divided into segments o Each segment has a set of muscles o Contract against coelomic fluid hydrostatic skeleton Closed circulatory system with 5 pumping vessels hearts Alimentary canal with specialized regions Figure 33 24 o Cerebral ganglia functions as a rudimentary brain o Metanephridium excretory tubes that remove wastes from blood and coelomic fluid o Ventral nerve chord with segmented ganglia Annelid Diversity Table 33 4 o Oligochaete o Polychaetes Figure 33 22 Figure 33 25 Clicker Q Cnidarians use to immobilize or trap prey o A Cnidocytes Concept 33 4 Ecdysozoans are the most species rich animal group Phylum Arthropoda 2 out of 3 known species of animals are arthropods Table 33 5 General Characteristics of Arthropods Arthropod body is covered by an exoskeleton made of chitin o When an arthropod grows it sheds the exoskeleton by a process called ecdysis Arthropods have an open circulatory system o Hemolymph is circulated into spaces surrounding tissues Variety of gas exchange organs o Consists of ticks spiders mites scorpions and horseshoe crabs o Spiders are the most diverse in this subphylum o Gills o Tracheal tubes o Book lungs Subphylum Cheliceriformes Figures 33 31 and 33 32 Arachnid Anatomy Spiders Body has 2 regions o Cephalothorax o Abdomen
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