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Chapter 23 Animal Diversity I: Invertebrates Lecture Outlines by Gregory Ahearn, University of North Florida Copyright © 2011 Pearson Education Inc. Chapter 23 At a Glance 23.1 What Are the Key Features of Animals? 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? 23.3 What Are the Major Animal Phyla? Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.1 What Are the Key Features of Animals? Animals possess all of the following characteristics – Multicellularity – Their cells lack a cell wall – They obtain energy by consuming other organisms – Most reproduce sexually – They are motile at some point in the life cycle – They are able to respond rapidly to external stimuli Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Most animal phyla that currently populate Earth were present by the Cambrian period (544 million years ago) – The scarcity of pre-Cambrian fossils led systematists to search for clues about the evolutionary history of animals by examining features of: –Anatomy –Embryological development –DNA sequences Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Certain features represent evolutionary milestones, and mark major branching points on the animal evolutionary tree – The appearance of tissues – The appearance of body symmetry – Protostome and deuterostome development Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. An Evolutionary Tree of Some Major Animal Phyla Fig. 23-1 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Lack of tissues separates sponges from all other animals – Tissues are groups of similar cells that carry out a specific function (e.g., muscle) – Sponges are the only modern-day animals that lack tissues – Individual cells in sponges may be specialized, but they act independently and are not organized into true tissues – Sponges and all remaining tissue-containing phyla arose from an ancient common ancestor without tissues Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Animals with tissues exhibit either radial or bilateral symmetry – Symmetrical animals have an upper (dorsal) surface and a lower (ventral) surface – Symmetrical animals are divided into two groups: –Animals that exhibit radial symmetry –Animals that exhibit bilateral symmetry Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Animals with radial symmetry can be divided into roughly equal halves by any plane that passes through the central axis – Animals with radial symmetry have two embryonic tissue (germ) layers – Ectoderm, which is an outer layer that covers the body, lines its inner cavities, and forms the nervous system – Endoderm, which is an inner layer that lines most hollow organs – Bilaterally symmetrical animals have three embryonic tissue (germ) layers – A layer of mesoderm between the ectoderm and endoderm forms muscles, and the circulatory and skeletal systems Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Bilaterally symmetrical animals have heads – Animals with bilateral symmetry can be divided into mirror-image halves only along one plane that runs down the midline – These animals exhibit cephalization, the concentration of sensory organs and a brain in a well-defined head, with definite anterior (head) and posterior (which may feature a tail) regions Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Body Symmetry and Cephalization central axis anterior plane of symmetry plane of symmetry posterior (a) Radial symmetry (b) Bilateral symmetry Fig. 23-2 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Most bilateral animals have body cavities – Body cavities are fluid-filled cavities between the digestive tube and the outer body wall – Body cavities have a variety of functions –They can act as a skeleton, providing support for the body and a framework against which muscles can act –They can form a protective buffer between the internal organs and the outside world –They can allow organs to move independently of the body wall Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Body cavity structure varies among phyla – The most common body cavity is a coelom, a fluid-filled body cavity that is completely lined with mesoderm –Phyla with animals that have this type of body cavity are called coelomates, and include annelids, arthropods, mollusks, echinoderms, and chordates (which include humans) Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Body cavity structure varies among phyla (continued) – A body cavity that is not completely surrounded by mesoderm is known as a pseudocoelom –Phyla with animals that have this type of body cavity are called pseudocoelomates and include roundworms, such as nematodes – Some bilateral animals have no body cavity and are known as acoelomates; they include the flatworms Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Body Cavities The body cavity is completely lined with tissue derived from mesoderm (a) “True” coelom (annelids, chordates) The body cavity is partially, but not completely, lined with tissue derived from mesoderm There is no cavity between the body wall and digestive tract body wall body wall coelom pseudocoelom digestive tract digestive tract digestive tract digestive cavity digestive cavity digestive cavity (b) “False” or pseudocoelom (roundworms) body wall (c) No coelom (cnidarians, flatworms) Fig. 23-3 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Bilateral organisms develop in one of two ways based on embryological development – Protostome development – In these animals, the body cavity forms within the space between the body wall and the digestive cavity – These animals include nematodes, arthropods, annelids, and mollusks – Deuterostome development – In these animals, the body cavity forms as an outgrowth of the digestive cavity – Echinoderms and chordates are deuterostomes Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Author Animation: The Architecture of Animals Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Protostomes include two distinct evolutionary lines – Ecdysozoans – Bodies are covered by an outer layer that is periodically shed – Examples include the arthropods and roundworms – Lophotrochozoans – This group has a lophophore (a special feeding structure) as well as a phyla that passes through a trochophore larva developmental stage – Examples include mollusks, annelids, and flatworms Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Animals probably originated from ancestral colonial protists Present day biologists recognize about 27 phyla of animals Most animals are invertebrates (lack a vertebral column) Less than 3% of all known animals are vertebrates (possess a vertebral column) Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Table 23-1, 1 of 2 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Table 23-1, 2 of 2 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Sponges have a simple body plan – Sponges belong to the phylum Porifera and are found in most marine and aquatic environments –Sponges do not move, but occur in a variety of sizes and shapes –They may reproduce asexually by budding, where the adult produces miniature versions of itself that drop off and assume an independent existence –They may reproduce sexually through fusion of sperm and eggs Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Diversity of Sponges Fig. 23-4 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Sponges lack true tissues and organs – The sponge body is perforated by tiny pores through which water passes, and by fewer, large openings through which water is expelled – As water passes through the sponge, oxygen is extracted, and microorganisms are filtered out and digested by individual cells Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Sponge cells are specialized for different functions – Epithelial cells are flat cells that cover the outer body surface – Pore cells are modified epithelial cells that regulate the flow of water through pores – Collar cells are flagellated cells that maintain water flow through the sponge – Amoeboid cells are motile cells that digest and distribute nutrients, produce reproductive cells, and secrete skeletal projections called spicules Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Body Plan of Sponges (water flow out of the sponge) epithelial cell spicules pore (water flow into the sponge) amoeboid cell pore cell collar cell (water flow) Fig. 23-5 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Some sponges contain chemicals useful to humans – A number of chemicals within sponges have proved to be valuable medicines –The drug spongistatin is an emerging treatment for the fungal infections that sicken AIDS patients –Some medicines derived from sponges include some promising new cancer drugs Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Cnidarians are well-armed predators – Sea jellies, sea anemones, corals, and hydrozoans belong to the phylum Cnidaria – These animals are mostly marine and are all carnivorous predators – The cells of cnidarians are arranged into distinct tissues, including a contractile muscle-like tissue and an organized nerve net Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Cnidarians are well-armed predators (continued) – The nerve net of cnidarians branches throughout the body and controls the contractile tissue to bring about movement and feeding behavior – Most cnidarians lack true organs and have no brain Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Cnidarian Diversity Fig. 23-6 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Cnidarians have two body plans: the polyp and the medusa – Many species have life cycles that include both body plans – Polyps and medusae develop from two germ layers—the endoderm and the ectoderm—with a jelly-like substance between the layers – The polyp is attached to rocks, while the medusa floats in the water; both have tentacles with cnidocytes, specialized cells that function in defense and the capture of prey Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Polyp and Medusa mouth lining of gastrovascular cavity lining of gastrovascular cavity gastrovascular cavity tentacle body wall body wall tentacle gastrovascular cavity foot (a) Polyp mouth (b) Medusa Fig. 23-7 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Cnidarians have stinging cells called cnidocytes that are used to capture prey and for defense – Cnidocytes contain a finely coiled filament that is explosively expelled when the trigger is touched –Some filaments inject poison into the prey –Others either stick to or entangle small prey –The venom of some can cause extreme pain or death in humans Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Cnidarian Weaponry: The Cnidocyte trigger filament trigger nuclei (b) Cnidocytes Biology: Life on Earth, 9e Fig. 23-8 Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Cnidarians have a gastrovascular cavity, a saclike digestive chamber with a single opening that serves as both a mouth and an anus – Tentacles force the prey through the opening into the gastrovascular cavity – Digestive enzymes secreted into this cavity break down some of the food, and further digestion occurs within the cells lining the cavity – Undigested wastes are expelled from the opening when digestion is completed Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Many corals secrete hard skeletons – In many coral species, polyps form colonies –Colonial polyps secrete a hard external skeleton of calcium carbonate –The skeleton remains after the polyp dies –New polyps build on the skeletal remnants of earlier generations – Coral reefs are found in both cold and warm oceans, and provide undersea habitats that support a wealth of diversity Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Comb jellies belong to the phylum Ctenophora – These animals resemble some cnidarians, but form, instead, a distinct evolutionary lineage – The comb jellies use cilia to move – All comb jellies are carnivorous, eating tiny invertebrate animals that they capture with sticky tentacles – Most comb jellies are hermaphroditic and can release both eggs and sperm into seawater; fertilized eggs gradually develop into larvae and then adults Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Flatworms may be parasitic or free living – Flatworms are bilaterally symmetrical and belong to the phylum Platyhelminthes – Many species are parasites, organisms that live in or on the body of another organism – Non-parasitic, free-living flatworms inhabit aquatic, marine, and moist terrestrial habitats – Flatworms can reproduce both sexually and asexually; most are hermaphroditic, having both male and female sexual organs Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Flatworms have organs but lack respiratory and circulatory systems – They possess a distinct head, along with sensory organs – The eyespots of freshwater planarians detect light and dark – Their nervous system consist of clusters of nerve cells called ganglia (singular: ganglion) in the head, forming a simple brain – They have paired nerve cords that extend the length of the body and conduct nerve signals to and from the ganglia Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Flatworms have organs but lack respiratory and circulatory systems (continued) – In the absence of a respiratory system, gas exchange is accomplished by diffusion between body cells and the environment – In the absence of a circulatory system, the digestive cavity has a branching structure that reaches all parts of the body and allows digested nutrients to diffuse into nearby cells Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Flatworms are bilaterally symmetrical, rather than radially symmetrical – This body plan is accompanied by cephalization, where sense organs are concentrated in the anterior portion of the body – This enhances an animal’s ability to respond appropriately to any stimuli that it encounters Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Some flatworms are harmful to humans – Tapeworms can infect people who eat improperly cooked beef, pork, or fish that has been infected by the worms –Tapeworm larvae form encapsulated resting structures, called cysts, in the muscles of these animals –The cysts hatch in the human digestive tract, and the young tapeworms attach themselves to the lining of the intestine Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Some flatworms are harmful to humans (continued) –Tapeworms may grow to a length of more than 20 feet (7 meters), absorbing nutrients across their outer surface –They release eggs that are shed in the hosts feces, continuing the infective cycle Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Life Cycle of the Human Pork Tapeworm 1 A human eats poorly cooked pork with live cysts 2 A larval tapeworm is liberated by digestion and attaches to the human’s intestine adult tapeworm 6 inches head (attachment site) 3 The tapeworm matures in a human intestine, producing a series of reproductive segments; each segment contains both male and female sex organs 8 The larvae form cysts in pig muscle 4 Eggs are shed from the posterior end of the worm and are passed with human feces 5 A pig eats food contaminated by infected feces 7 The larvae migrate through blood vessels to pig muscle Biology: Life on Earth, 9e 6 Larvae hatch in the pig’s intestine Fig. 23-10 Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Some flatworms are harmful to humans (continued) – Another group of parasitic flatworms is the flukes –Flukes have complex life cycles that include an intermediate host, such as a snail –Blood flukes cause schistosomiasis, which causes symptoms such as diarrhea, anemia, and possible brain damage –As many as 200 million people worldwide may be infected with flukes Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Flatworm Diversity Fig. 23-9 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Annelids are segmented worms and belong to the phylum Annelida – The annelid body is divided into a series of repeating units (segmentation) –The segments contain identical copies of nerves, excretory structures, and muscles that allows for complex movement – Annelids have a fluid-filled coelom –The coelom functions as a hydrostatic skeleton, where pressurized fluid provides a framework against which muscles can act Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Many annelids reproduce sexually – Some species are hermaphroditic; others have separate sexes – During copulation, sperm are transferred from one individual to the other – In hermaphroditic species, sperm transfer may be mutual, with each partner donating and receiving sperm – Some annelids reproduce asexually by fragmentation – The body breaks into two pieces, each of which regenerates the missing part Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Annelids have a closed circulatory system (blood is confined to the heart and blood vessels) – The circulatory system distributes gases and nutrients throughout body – The blood is filtered and wastes are removed by excretory organs called nephridia Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? The annelid nervous system consists of: – A simple brain in the head – A series of repeating paired segmental ganglia joined by a pair of ventral nerve cords extending the length of the body Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? The annelid digestive system consists of a tubular gut with two openings—a mouth and an anus Digestion occurs in a series of compartments –Pharynx: draws in food –Esophagus: conducts food to crop –Crop: stores food –Gizzard: grinds food –Intestine: absorbs digested nutrients Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. An Annelid, The Earthworm coelom nephridia intestine excretory pore ventral nerve cord anus coelom brain mouth Biology: Life on Earth, 9e pharynx ventral hearts esophagus crop gizzard intestine vessel ventral nerve cord Fig. 23-11 Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? The annelid species fall into three main subgroups – Oligochaetes – Polychaetes – Leeches Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Oligochaetes – These worms live in moist terrestrial habitats – This group includes earthworms and its relatives –As a result of their extensive tunneling through soils, earthworms have major roles in aerating the soil and mixing its organic matter, which are favorable activities for plant growth Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Polychaetes – Most polychaetes live in the ocean –Some have tubes from which they project feathery gills used for gas exchange and to filter the water for microscopic food –Others have segmental, paired, fleshy paddles that are used for locomotion Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Leeches – Leeches live in fresh water or moist terrestrial habitats – They are either carnivorous (prey on smaller invertebrates) or parasitic (suck the blood of larger animals) Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Diverse Annelids Fig. 23-12 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Most mollusks have shells – The phylum Mollusca consists of clams, snails, and cephalopods – Most mollusks have open circulatory systems (blood is not confined to the heart and blood vessels) – Blood percolates through a hemocoel (or blood cavity), bathing the internal organs directly – Mollusks have an extension of the body wall, called a mantle, that forms a chamber for the gills and, in shelled species, secretes the shell Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? The mollusk nervous system is similar to that of annelids (ganglia connected by ventral nerves); however, more of the ganglia are concentrated in the head Mollusks reproduce sexually –Some species have separate sexes –Others are hermaphroditic Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. A Bivalve Mollusk shell heart kidney hinge adductor muscle stomach anus mouth gills foot gonad Biology: Life on Earth, 9e mantle intestine Fig. 23-13 Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? The three classes of mollusks are: – Gastropods – Bivalves – Cephalopods Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Gastropods are one-footed crawlers – The snails and slugs are collectively known as gastropods –They have a muscular foot for locomotion –They may possess a shell, but not all gastropods are shelled –They feed using a radula, a flexible ribbon studded with spines that scrape algae from rocks or grasp larger plants or prey –Most use their skin and gills for respiration, but terrestrial mollusks have a simple lung Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Diversity of Gastropod Mollusks Fig. 23-14 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Bivalves are filter feeders – Bivalves include scallops, oysters, mussels, and clams –They live in fresh water and marine habitats –They possess two shells that can be clamped shut by a strong muscle –They are filter feeders and use gills for both feeding and respiration –Most have a muscular foot used for burrowing or for attaching to rocks Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Diversity of Bivalve Mollusks Fig. 23-15 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Cephalopods are marine predators – The cephalopods include octopuses, nautiluses, cuttlefish, and squids –All cephalopods are predatory carnivores, and all are marine –They have large, complex brains and are capable of learning –They possess highly developed sensory systems –Some may have a shell (e.g., nautiluses) Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Cephalopods are marine predators (continued) – Cephalopods have tentacles with chemosensory abilities and suction disks –The tentacles are used for locomotion and to capture prey – These animals are able to move rapidly by forcefully expelling water from the mantle cavity – They possess closed circulatory systems Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Diversity of Cephalopod Mollusks Fig. 23-16 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Arthropods are the most diverse and abundant animals – The phylum Arthropoda includes insects, arachnids, myriopods, and crustaceans – Arthropods have appendages and an exoskeleton (external skeleton) –The exoskeleton is secreted by the epidermis (the outer layer of skin) –It is composed primarily of protein and chitin (a polysaccharide) Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Arthropods have appendages and an exoskeleton (continued) – The exoskeleton: –Protects against predators –Provides rigid attachment sites for muscles, but are thin and flexible at joints to increase the range of movement of the appendages –Provides a watertight covering – The exoskeleton must be molted (shed) periodically so that the animal can grow in size Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Exoskeleton Allows Precise Movements Fig. 23-17 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Exoskeleton Must Be Molted Fig. 23-18 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Arthropods have specialized segments and adaptations for active lifestyles The insect body is divided into three distinct regions, each specialized for different functions –Head (front region): for feeding and sensing the environment –Thorax (middle region): the segment where structures used for locomotion (wings, legs) are attached –Abdomen (rear region): contains digestive structures Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Segments Are Fused and Specialized in Insects antennae head thorax abdomen compound eye mouth parts wing Fig. 23-19 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Arthropods have specialized segments and adaptations for active lifestyles (continued) Arthropods have efficient gas exchange – Aquatic arthropods (crustaceans) have gills (thin, external respiratory membranes) – Terrestrial arthropods have either: – Lungs, such as in arachnids – Tracheae (singular, trachea): a network of narrow, branching respiratory tubes Most arthropods have an open circulatory system Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Arthropods have complex sensory and nervous systems, responsible for finely coordinated movement and complex behaviors – The nervous system consists of the brain, which is composed of fused ganglia, and a series of additional ganglia along the length of the body that are linked by a ventral nerve cord – Arthropods possess well-developed sensory structures, including compound eyes, and chemical and tactile receptors Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Arthropods Possess Compound Eyes Fig. 23-20 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Insects are the only flying invertebrates – They are the most abundant and diverse class of arthropods – They are the only invertebrates that are capable of flight – The ability to fly has contributed to the enormous success of insects –It helps insects escape predators –It allows insects to find widely dispersed food – Insects use tracheae for gas exchange Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Diversity of Insects Fig. 23-21 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Insects undergo metamorphosis, a radical change from a juvenile body form to an adult body form – In many insects, the juvenile is a larva, and has a worm-shaped body form –Examples include maggots (housefly larva) and caterpillars (moth or butterfly larva) Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? In insects with complete metamorphosis, developmental stages include egg larva (feeding stage) pupa (nonfeeding stage) adult – Houseflies, moths, and butterflies undergo complete metamorphosis In insects with incomplete metamorphosis, developmental stages include egg nymph (feeding stage that resembles the adult) adult – Grasshoppers and crickets undergo incomplete metamorphosis Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Insects are divided into several dozen groups; three of these groups include: – Butterflies and moths – Bees, ants, and wasps – Beetles Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Butterflies and moths – These are the most conspicuous and beststudied group of insects – Butterflies fly during the day; moths fly at night – The evolution of butterflies and moths has been closely tied to the evolution of flowering plants, which depend on these flying insects for pollination Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Bees, ants, and wasps – This group of insects is equipped with a stinger that extends from the abdomen and can be used to inject venom into the victim of a sting – Representatives of this group (e.g., bees and ants) have complex social behavior in which individuals specialize in particular tasks such as foraging, defense, reproduction, or rearing larvae Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Beetles – One-third of all known insect species are beetles – They have a hard, protective, exoskeletal structure that covers their wings – Representatives may be destructive agricultural pests or predators that are used to control other insect pests Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Most arachnids are predatory meat eaters – The arachnids include spiders, mites, ticks, and scorpions – Arachnids lack antennae – Arachnids have eight walking legs – Most arachnids are carnivorous (feed on blood or predigested prey) Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Most arachnids are predatory meat eaters (continued) – Some arachnids, such as spiders and scorpions, inject paralyzing venom into prey – Arachnids breathe by using tracheae, lungs, or both – Some have simple image-forming eyes, each with a single lens – In arachnids, abdominal glands produce protein threads (silk) that is used to weave webs – Spiders have sensory hairs that are sensitive to touch, smell, or taste, and aid in detecting predators or prey Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Diversity of Arachnids Fig. 23-22 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Myriapods have many legs – The myriapods include the centipedes and millipedes –They have one pair of antennae –They have simple light-detecting eyes –They respire by means of tracheae – Centipedes have one pair of legs per body segment – Millipedes have two pairs of legs per body segment Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Myriapods (continued) – Myriapods inhabit terrestrial environments, living in the soil or in leaf litter – Centipedes are usually carnivorous –They capture prey with their frontmost legs, and inject poison into the prey – Millipedes feed on decaying vegetation –They secrete a foul-smelling, distasteful liquid when attacked Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Diversity of Myriapods Fig. 23-23 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Most crustaceans are aquatic – Crustaceans include crabs, crayfish, lobsters, shrimp, and barnacles –They possess two pairs of antennae –Most have compound eyes –Most respire by means of gills Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Diversity of Crustaceans Fig. 23-24 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Roundworms are abundant and mostly tiny – Most roundworms are microscopic, but some parasitic forms reach a meter in length – Most have an elongate body that is protected by a cuticle that must be molted periodically – They have a tubular gut with a separate mouth and anus – They have sensory organs that transmit information to a simple brain Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. A Freshwater Nematode posterior end intestine anterior end ovary vagina eggs mouth cuticle Fig. 23-25 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Roundworms are Pseudocoelomates and have a simplified body plan – They lack circulatory and respiratory systems –Gas exchange occurs by diffusion between body cells and the environment – They mostly reproduce sexually –A male places sperm in the body of a female – Most roundworms are free-living and break down organic matter Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? A few roundworms are harmful to humans – Some roundworms are parasitic –Hookworm larvae bore into human feet and travel to the intestine, where they cause continuous bleeding –Trichinella worms infect people who eat improperly cooked infected pork; their larvae invade blood vessels and muscles, causing bleeding and muscle damage –Heartworms can be transmitted to dogs by the bite of an infected mosquito Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Some Parasitic Nematodes Fig. 23-26 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Echinoderms have a calcium carbonate skeleton The phylum Echinodermata includes sand dollars, sea urchins, sea stars, sea cucumbers, and sea lilies – Echinoderm larvae exhibit bilateral symmetry; adults show radial symmetry – They exhibit deuterostome development – They possess an endoskeleton (internal skeleton) that sends projections through the skin Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Diversity of Echinoderms Fig. 23-27 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Echinoderms have a unique water-vascular system – It consists of the sieve plate, a circular central canal, several radial canals, and numerous tube feet – The water-vascular system functions in locomotion, respiration, and food capture Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Water-Vascular System of Echinoderms sieve plate stomach canals ampulla tube feet (a) Starfish body plan (b) Starfish consuming a mussel Fig. 23-28 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Echinoderms have a primitive nervous system with no distinct brain – The nervous system consists of a nerve ring, radial nerves, and a nerve network running through the epidermis –Sea stars have simple light and chemical receptors –Some brittle star species have lens-containing light receptors Echinoderms lack a circulatory system Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? Most echinoderms reproduce sexually – They shed eggs and sperm into water – Fertilization is external Many echinoderms are able to regenerate lost body parts – A sea star arm with part of the central body attached is able to form a whole animal Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 23.3 What Are the Major Animal Phyla? The phylum Chordata includes two invertebrate groups (the sea squirts and the lancelets) plus the vertebrates Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc.