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Animal Characteristics • Heterotrophs – must ingest others for nutrients • Multicellular – complex bodies • No cell walls – allows active movement • Sexual reproduction – no alternation of generations – no haploid gametophyte Animal Evolution Cnidaria Porifera sponges jellyfish Nematoda Platyhelminthes Annelida Mollusca Echinodermata Arthropoda flatworms roundworms mollusks segmented worms redundancy, segmentation specialization, mobility insects spiders starfish Chordata vertebrates body & brain backbone size, mobility body size endoskeleton coelom digestive sys radial body cavity body complexity digestive & repro sys bilateral symmetry tissues multicellularity Ancestral Protist distinct body plan; cephalization specialized structure & function, muscle & nerve tissue specialization & body complexity bilateral Body Cavity • Space for organ system development – increase digestive & reproductive systems • increase food capacity & digestion • increase gamete production • Coelem – mesoderm & endoderm interact during development – allows complex structures to develop in digestive system • ex. stomach acoelomate ectoderm mesoderm endoderm pseudocoelomate ectoderm mesoderm endoderm pseudocoel coelomate ectoderm mesoderm coelom cavity endoderm protostome vs. deuterostome • The basic organization of germ layers differs between radiata and bilateria. • The radiata are said to be diploblastic because they have two germ layers. – The ectoderm, covering the surface of the embryo, give rise to the outer covering and, in some phyla, the central nervous system. – The endoderm, the innermost layer, lines the developing digestive tube, or archenteron, and gives rise to the lining of the digestive tract and the organs derived from it, such as the liver and lungs of vertebrates. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The bilateria are triploblastic. – The third germ layer, the mesoderm lies between the endoderm and ectoderm. – The mesoderm develops into the muscles and most other organs between the digestive tube and the outer covering of the animal. The Bilateria can be divided by the presence or absence of a body cavity (a fluid-filled space separating the digestive tract from the outer body wall) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Animal Evolution Cnidaria Porifera sponges jellyfish Nematoda Platyhelminthes Annelida Mollusca Echinodermata Arthropoda flatworms roundworms mollusks segmented worms redundancy, segmentation specialization, mobility insects spiders starfish Chordata vertebrates body & brain backbone size, mobility body size endoskeleton coelom digestive sys radial body cavity body complexity digestive & repro sys bilateral symmetry tissues multicellularity Ancestral Protist distinct body plan; cephalization specialized structure & function, muscle & nerve tissue specialization & body complexity bilateral Invertebrate: Platyhelminthes • Flatworms – tapeworm, planaria – mostly parasitic – bilaterally symmetrical • have right & left & then have head (anterior) end & posterior end Animals now face the world – cephalization = development of brain head on! – concentration of sense organs in head • increase specialization in body plan ectoderm acoelomate mesoderm endoderm Flatworms • Members of phylum Platyhelminthes live in marine, freshwater, and damp terrestrial habitats • Although flatworms undergo triploblastic development, they are acoelomates • They are flattened dorsoventrally and have a gastrovascular cavity • Gas exchange takes place across the surface, and protonephridia regulate the osmotic balance • Flatworms are divided into four classes: – Turbellaria (mostly free-living flatworms) – Monogenea (monogeneans) – Trematoda (trematodes, or flukes) – Cestoda (tapeworms) Table 33-2 Turbellarians • Turbellarians are nearly all free-living and mostly marine • The best-known turbellarians are commonly called planarians Fig. 33-9 • Planarians have light-sensitive eyespots and centralized nerve nets • The planarian nervous system is more complex and centralized than the nerve nets of cnidarians • Planarians are hermaphrodites and can reproduce sexually, or asexually through fission Fig. 33-10 Pharynx Gastrovascular cavity Mouth Eyespots Ganglia Ventral nerve cords Monogeneans and Trematodes • Monogeneans and trematodes live as parasites in or on other animals • They parasitize a wide range of hosts, and most have complex life cycles with alternating sexual and asexual stages • Trematodes that parasitize humans spend part of their lives in snail hosts • Most monogeneans are parasites of fish Fig. 33-11 Male Female Human host 1 mm Motile larva Ciliated larva Snail host Tapeworms • Tapeworms are parasites of vertebrates and lack a digestive system • Tapeworms absorb nutrients from the host’s intestine • Fertilized eggs, produced by sexual reproduction, leave the host’s body in feces Scolex Proglotid 200 µm Hooks Proglottids with reproductive structures Sucker Scolex Invertebrate: Nematoda • Roundworms – bilaterally symmetrical – body cavity • pseudocoelom = simple body cavity • digestive system – tube running through length of body (mouth to anus) – many are parasitic • hookworm C. elegans Nematodes • Nematodes, or roundworms, are found in most aquatic habitats, in the soil, in moist tissues of plants, and in body fluids and tissues of animals • They have an alimentary canal, but lack a circulatory system • Reproduction in nematodes is usually sexual, by internal fertilization Fig. 33-25 25 µm • Some species of nematodes are important parasites of plants and animals Encysted juveniles Muscle tissue 50 µm Figure 15.06 Guinea worms • Guinea worm infections (also referred to as Dracunculiasis) are now confined to subSaharan Africa. Adults are threadlike nematode worms that can grow to 1 meter in length. • The adult lives in humans and the intermediate host is tiny crustaceans. • Humans become infected when they drink water containing the crustaceans. Guinea worms • The immature worm penetrates the gut wall and wanders through the body, maturing and growing. • After about a year the female makes her way to the surface of the skin (usually in the legs) causing very painful blistering. Guinea worms • To ease the pain, sufferers immerse their feet in water. This bursts the blisters and the female worm then protrudes from the sore and lays her eggs, thus continuing the life cycle. Guinea worms • There is no cure for Guinea worms and the only way to remove one is to slowly over the course of weeks wind the worm out on a stick. • If the worm breaks, a serious bacterial infection results. Ascaris lumbricoides Invertebrate: Mollusca • Mollusks – – – – slugs, snails, clams, squid bilaterally symmetrical (with exceptions) soft bodies, mostly protected by hard shells true coelem • increases complexity & specialization of internal organs Molluscs • Phylum Mollusca includes snails and slugs, oysters and clams, and octopuses and squids • Most molluscs are marine, though some inhabit fresh water and some are terrestrial • Molluscs are soft-bodied animals, but most are protected by a hard shell • All molluscs have a similar body plan with three main parts: – Muscular foot – Visceral mass – Mantle • Many molluscs also have a water-filled mantle cavity, and feed using a rasplike radula Fig. 33-15 Nephridium Visceral mass Coelom Heart Intestine Gonads Mantle Stomach Shell Mantle cavity Mouth Radula Anus Gill Foot Nerve cords Esophagus Mouth Radula • Most molluscs have separate sexes with gonads located in the visceral mass • The life cycle of many molluscs includes a ciliated larval stage called a trochophore • There are four major classes of molluscs: – Polyplacophora (chitons) – Gastropoda (snails and slugs) – Bivalvia (clams, oysters, and other bivalves) – Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses) Table 33-3 Fig. 33-16 Fig. 33-17 (a) A land snail (b) A sea slug • Most gastropods are marine, but many are freshwater and terrestrial species • Most have a single, spiraled shell • Slugs lack a shell or have a reduced shell • The most distinctive characteristic of gastropods is torsion, which causes the animal’s anus and mantle to end up above its head Fig. 33-18 Mantle cavity Anus Mouth Stomach Intestine Fig. 33-20 Mantle Hinge area Coelom Gut Heart Adductor muscle Digestive gland Anus Mouth Excurrent siphon Shell Palp Foot Mantle cavity Gonad Gill Water flow Incurrent siphon Fig. 33-21 Octopus Squid Chambered nautilus • Cephalopods have a closed circulatory system, well-developed sense organs, and a complex brain • Shelled cephalopods called ammonites were common but went extinct at the end of the Cretaceous Invertebrate: Annelida • Segmented worms – earthworms, leeches – segments • increase mobility • redundancy in body sections – bilaterally symmetrical – true coelem fan worm leech Annelids • Annelids have bodies composed of a series of fused rings • The phylum Annelida is divided into three classes: – Oligochaeta (earthworms and their relatives) – Polychaeta (polychaetes) – Hirudinea (leeches) Table 33-4 Oligochaetes • Oligochaetes (class Oligochaeta) are named for relatively sparse chaetae, bristles made of chitin • They include the earthworms and a variety of aquatic species • Earthworms eat through soil, extracting nutrients as the soil moves through the alimentary canal • Earthworms are hermaphrodites but cross-fertilize Fig. 33-22 Epidermis Cuticle Coelom Circular muscle Septum (partition between segments) Metanephridium Longitudinal muscle Anus Dorsal vessel Chaetae Intestine Fused nerve cords Ventral vessel Nephrostome Metanephridium Clitellum Esophagus Pharynx Giant Australian earthworm Cerebral ganglia Crop Intestine Gizzard Mouth Subpharyngeal ganglion Blood vessels Ventral nerve cord with segmental ganglia Polychaetes • Members of class Polychaetes have paddle-like parapodia that work as gills and aid in locomotion Parapodia Leeches • Members of class Hirudinea are blood-sucking parasites, such as leeches • Leeches secrete a chemical called hirudin to prevent blood from coagulating Invertebrate: Arthropoda • Spiders, insects, crustaceans – most successful animal phylum – bilaterally symmetrical – segmented • specialized segments • allows jointed appendages – exoskeleton • chitin + protein Arthropod groups arachnids 8 legs, 2 body parts spiders, ticks, scorpions crustaceans gills, 2 pairs antennae crab, lobster, barnacles, shrmp insects 6 legs, 3 body parts Fig. 33-37a Fig. 33-37b Fig. 33-37c Fig. 33-37d Fig. 33-37e Invertebrate: Echinodermata • Starfish, sea urchins, sea cucumber – radially symmetrical as adults – spiny endoskeleton loss of bilateral symmetry? – deuterostome Invertebrate quick check… Invertebrates: Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata • Which group includes snails, clams, and squid? • Which group is the sponges? • Which are the flatworms? …segmented worms? …roundworms? • Which group has jointed appendages & an exoskeleton? • Which two groups have radial symmetry? • What is the adaptive advantage of bilateral symmetry? • Which group has no symmetry?
