Invertebrates

Invertebrates Nearly all animals are invertebrates (95%) Invertebrates are animals that lack backbones Let’s take a survey of the major phyla of animals! 

Single-celled, protistanlike ancestors Chordates Major Animal Phyla Echinoderms Arthropods Annelids Coelomate Ancestry Mollusks Rotifers Roundworms Bilateral Ancestry Flatworms Radial Ancestry Cnidarians Sponges Multicelled Ancestry Figure 25.2 Page 415 Single-celled, protistanlike ancestors

Symmetry Bilateral Radial posterior dorsal ventral anterior Figure 25.3 Page 416

The Gut Region where food is digested and then absorbed Saclike gut One opening for taking in food and expelling waste Complete digestive system Opening at both ends; mouth and anus

Body Cavities - Acoelomate epidermis gut cavity no body cavity; region between gut and body wall packed with organs Figure 25.4a Page 417

Body Cavities - Pseudocoel epidermis gut cavity unlined body cavity (pseudocoel) around gut Figure 25.4b Page 417

lined body cavity (coelom) Body Cavities - Coelom gut cavity lined body cavity (coelom) peritoneum Figure 25.4c Page 417

Segmentation Repeating series of body units Units may or may not be similar to one another Earthworms - segments appear similar Insects - segments may be fused and/or have specialized functions

Animal Origins Originated during the Precambrian (1.2 billion - 670 million years ago) From what? Two hypotheses: Multinucleated ciliate became compartmentalized Cells in a colonial flagellate became specialized

Phylum Porifera Representative organism: sponge Have no true tissues (Parazoa) Their cells are relatively unspecialized Sponges are sessile (nonmotile) Ancient Greeks believed them to be plants Filter-feeders: Trap food from the water that flows through them Most sponges are hermaphrodites Each individual produces both sperm and eggs

Sponge Structure Figure 25.7a Page 419 water out glasslike structural elements amoeboid cell pore central cavity semifluid matrix flattened surface cells water in Figure 25.7a Page 419 flagellum microvilli nucleus

Phylum Cnidaria Have stinging cells inside of nematocysts On tentacles capsule’s lid at free surface of epidermal cell trigger barbed thread inside capsule Figure 25.8 Page 420 nematocyst

Phylum Cnidaria Representative Organisms: Jellyfish & Sea Anemones Have true tissues and radial symmetry Body plan: sac with a central digestive compartment known as the gastrovascular cavity (mouth & anus) 2 variations on the body plan: Polyp: sessile, mouth up, waits for prey (sea anemone) Medusa: floats, mouth down (jellyfish) Attack prey with tentacles

outer epithelium (epidermis) inner epithelium (gastrodermis) Two Main Body Plans Polyp outer epithelium (epidermis) mesoglea (matrix) Medusa inner epithelium (gastrodermis) Figure 25.9 Page 420

Obelia Life Cycle (Hydrozoan) female medusa male medusa reproductive polyp sperm ovum feeding polyp zygote polyp forming planula Figure 25.10 Page 421

Phylum Platyhelminthes Representative Organisms: Tapeworms, flukes, & planarians Bilateral symmetry Acoelomates – no body cavity enclosed by mesoderm Many are parasitic

Planarian Organ Systems flame cell nucleus pharynx cilia protonephridia fluid filters through membrane folds opening of tubule at body surface flame cell Fig. 25.11a,b Page 422

Planarian Organ Systems brain nerve cord oviduct ovary genital pore testis penis Fig. 25.11cd Page 422

Flukes: Class Trematoda Parasitic worms Complicated life cycle Larval stage infects a mollusk Adult infects a vertebrate Worms mate in human host Larvae bore into human skin Larvae form, leave snail Fertilized egg Asexual reproduction in intermediate host Ciliated larva Figure 25.14 Page 424 Southeast Asian blood fluke

Tapeworms: Class Cestoda Definitive host Larvae encysted in muscle tissue Scolex attaches to host intestinal wall Intermediate host Figure 25.15 Page 424 Mature proglottid with fertilized eggs

Phylum Nematoda Representative organism: roundworms Pseudocoelomate have a body cavity, but not encased by mesoderm Round worms with tapered ends Can be parasitic (trichinosis)

Roundworms (Nematoda) False coelom (pseudocoelomate) Complete digestive system pharynx intestine eggs in uterus gonad anus false coelom muscularized body wall Figure 25.13 Page 423

Two Coelomate Lineages Protostomes Mollusks Annelids Arthropods Deuterostomes Echinoderms Chordates

Cleavage Patterns Protostome embryo (spiral cleavage) Blastopore becomes mouth Deuterostome embryo (radial cleavage) Blastopore becomes anus In-text figure Page 426

Phylum Mollusca Representative organisms: Coelomates Protostomes: snails, slugs, oysters, clams, octopuses, squids Coelomates Have a true coelom Protostomes: Blastopore becomes mouth

Phylum Mollusca Body plan has 3 main parts: Muscular foot used for movement Visceral mass covering the internal organs Mantle covers the visceral mass (may produce a protective shell)

Closed circulatory system with heart and accessory heart Cuttlefish Body Plan Closed circulatory system with heart and accessory heart esophagus Figure 25.22 Page 429 digestive gland kidney stomach brain arm jaw mantle reproductive organ internal shell siphon ink sac heart accessory heart tentacle radula anus gill

Phylum Annelida Representative Organism: earthworm Annelids have segmented bodies Metanephridia (similar to kidneys) Remove wastes from the blood Worms are hermaphrodites Produce both sperm and eggs Setae provide traction for burrowing in the soil Earthworms eat their way through the soil