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Kingdom Animalia General Features of Animals • Animals share many important characteristics, such as they are heterotrophs are multicellular and lack cell walls can move from place to place have diverse forms and habitats reproduce, mostly by sexual reproduction have a common pattern of development Have unique tissues The Animal Family Tree • Two Branches Parazoa • possess neither tissues nor organs and have no discernible symmetry Eumetazoa • have a definite shape and symmetry and, in most cases, tissues organized into organs and organ systems Parazoan Phylum- Porifera The Animal Family Tree • Eumetazoans are divided into two groups Radiata have radial symmetry and two embryological layers, an outer ectoderm and an inner endoderm. Bilateria have bilateral symmetry and a third embryological layer, the mesoderm. The animal family tree Five Key Transitions in Body Plan • The evolution of animals is marked by five key transitions in body plan 1. 2. 3. 4. 5. tissues bilateral symmetry body cavity deuterostome development segmentation Tissues • The presence of tissues is the first key transition in the animal body plan Parazoans lack defined tissues and organs • these animals exist as aggregates of cells with minimal intercellular coordination Eumetazons possess tissues Symmetry radial symmetry • any plane passing through the central axis divides the organism in halves that are approximate mirror images bilateral symmetry • the plan allows for specialization among body regions and more efficient movement Body Cavity • The evolution of a body cavity was an important step in animal evolution this internal space allowed for the support of organs, distribution of materials, and coordination of development for example, the digestive tract can be larger and longer Patterns of Development • Bilateral animals can be divided into two groups based on differences in the basic pattern of development protostomes include the flatworms, nematodes, mollusks, annelids, and arthropods deuterostomes include the echinoderms and the chordates deuterostomes evolved from protostomes more than 630 million years ago. Protostomes and Deuterostomes • There are two major kinds of coelomate animals representing two distinct evolutionary lines protostomes • the mouth develops from or near the blastopore deuterostomes • the anus forms from or near the blastopore; the mouth forms on another part of the blastula Embryonic development in protostomes and deuterostomes Segmentation • The subdivision of the body into segments is another key transition in the animal body plan in highly segmented animals, each segment can develop a more or less complete set of adult organ systems each segment can function as a separate locomotory unit Sponges: Animals Without Tissues • Sponges are members of the phylum Porifera their bodies a little more than masses of specialized cells embedded in a gel-like matrix the body of a sponge is perforated by many pores • choanocytes are flagellated cells that line the body cavity of the sponge and draw in water through the pores the sponge is a filter feeder which traps any food particles Cnidarians: Tissues Lead to Greater Specialization • Radiata are radially symmetrical and include two phyla Cnidaria comprises the hydra, jellyfish, corals, and anemones Ctenophora comprises the comb jellies • The members of the Radiata have a body plan that allows them to interact with their environment on all sides • A major evolutionary advance in the Radiata is extracellular digestion of food digestion begins outside of cells in a gut cavity called the gastrovascular cavity this form of digestion allows animals to digest an animal larger than itself Representative cnidarians Cnidarians: Tissues Lead to Greater Specialization • Cnidarians (phylum Cnidaria) are carnivores that capture prey with tentacles that ring their mouths these tentacles and, sometimes, the body surface bear stinging cells called cnidocytes within each cnidocyte is a harpoonlike barb, called a nematocyst, which cnidarians use to spear prey and retract it towards the tentacle the nematocyst can discharge so explosively that it is capable of piercing the hard shell of a crab Cnidarians: Tissues Lead to Greater Specialization • Cnidarians have two basic body forms medusae are a floating form polyps are a sessile form Cnidarians: Tissues Lead to Greater Specialization • Medusae are often called “jellyfish,” because of their gelatinous interior, or “stinging nettles,” because of their nematocysts • Polyps are pipe-shaped animals that usually attach to rock in corals, the polyps secrete a deposit of calcium carbonate in which they live The life cycle of Obelia, a marine colonial hydroid Solid Worms: Bilateral Symmetry • Body symmetry differs among the Eumetazoa radial symmetry bilateral symmetry Solid Worms: Bilateral Symmetry • Most bilaterally symmetrical animals have evolved a definitive head end this process is termed cephalization • Three embryonic layers ectoderm will develop into the outer coverings of the body and the nervous system mesoderm will develop into the skeleton and muscles endoderm will develop into the digestive organs and intestine Solid Worms: Bilateral Symmetry • Bilaterally symmetrical animals the largest phylum of these worms is the Phylum Platyhelminthes, which includes the flatworms • flatworms lack any internal cavity other than the digestive tract – this solid condition is called acoelomate Flatworms Solid Worms: Bilateral Symmetry • Most flatworms are parasitic but some are free-living flatworms range in size from less than a millimeter to many meters long • There are two classes of parasitic flatworms flukes tapeworms • The parasitic lifestyle has resulted in the eventual loss of features not used or needed by the parasite for example, parasites flatworms lack cilia in the adult stage and do not need eye spots this loss of features that lack adaptive purpose for parasitism is sometimes called degenerative evolution Life cycle of the human liver fluke, Clonorchis sinensis Solid Worms: Bilateral Symmetry • Those flatworms that have a digestive cavity, have an incomplete gut, one with only one opening • the gut branches throughout the body and is involved in both digestion and excretion • these flatworms are also capable of performing some extracellular digestion • The parasitic flatworms lack a gut entirely and absorb food directly through their body walls Roundworms: The Evolution of a Body Cavity • A key transition in the evolution of the animal body plan was the evolution of the body cavity • The evolution of an internal body cavity helped improve the animal body design in three areas circulation movement organ function Roundworms: The Evolution of a Body Cavity • There are three basic kinds of body plans found in bilaterally symmetrical animals acoelomates have no body cavity pseudocoelomates have a body cavity (called a pseudocoel) located between the mesoderm and the endoderm coelomates have a body cavity (called a coelom) that develops entirely within the mesoderm Figure 25.16 Three body plans for bilaterally symmetrical animals Roundworms: The Evolution of a Body Cavity • Seven phyla of bilaterally symmetrical animals have a pseudocoel the pseudocoel serves as a hydrostatic skeleton, a skeleton that gains its rigidity from fluids kept under pressure • muscles can work against this “skeleton” all pseudocoelomates lack a defined circulatory system most pseudocoelomates have a complete digestive tract Roundworms: The Evolution of a Body Cavity • The largest pseudocoelomate phylum is Nematoda, containing about 20,000 species the members of this phylum include nematodes, eelworms, and other roundworms nematodes are unsegmented, cylindrical worms covered by a flexible cuticle that is molted as they grow nematodes move in a whip-like fashion Roundworms: The Evolution of a Body Cavity • Another pseudocoelomate phylum is Rotifera Rotifers are small, aquatic organisms that have a crown of cilia at their heads the cilia help in both locomotion and feeding Mollusks: Coelomates • The mollusks, members of the phylum Mollusca, are the only coelomates without segmented bodies • The body of a mollusk is comprised of three regions a head-foot a visceral mass containing the body’s organs a mantle that envelopes the visceral mass and is associated with the gills Mollusks: Coelomates • There three major groups of mollusks gastropods—include the snails and slugs bivalves—include clams, oysters, and scallops cephalopods— include the octopuses and squids Mollusks: Coelomates • Mollusks have a unique feeding structure, called a radula the radula is a rasping tongue-like organ that bears rows of pointed, backward-curving teeth • In most mollusks, the outer surface of the mantle secretes a protective shell the shell has multiple layers comprised of protein, calcium, and pearl Annelids: The Rise of Segmentation • One of the early innovations in body plan to arise among the coelomates was segmentation segmentation is the building of a body from a series of similar segments • this body plan offers a lot of flexibility in that small changes to segments can produce a new kind of segment with different functions the first segmented animals to evolve were the annelid worms, phylum Annelida Annelids: The Rise of Segmentation • The basic body plan of an annelid is a tube within a tube the digestive tract is suspended within the tube of the coelom the tubes run from mouth to anus • There are three body plan characteristics repeated segments specialized segments connections Arthropods: Advent of Jointed Appendages • The most successful of all animal groups is the phylum Arthropoda, consisting of the arthropods these animals have jointed appendages in addition to joints, arthropods have an exoskeleton made of chitin • the muscles of arthropods attach to the interior of this outer shell • the shell offers protection against predators and water loss • Chitin cannot support much weight arthropod size is limited as a result • Arthropod bodies are segmented like annelids Segmentation in insects Arthropods: Advent of Jointed Appendages • Chelicerates are arthropods that lack jaws they include spiders, mites, scorpions, and horseshoe crabs • Mandibulates are arthropods with jaws, called mandibles they include the crustaceans, insects, centipedes, and millipedes Arthropods: Advent of Jointed Appendages • The chelicerate fossil record goes back 630 million years a surviving type of chelicerate from this period is the horseshoe crab Figure 25.27 Horseshoe crabs Arthropods: Advent of Jointed Appendages • The class Arachnida has 57,000 named species of arachnids, including spiders, ticks, mites, scorpions, and daddy longlegs arachnids have a pair of chelicerae, a pair of pedipalps, and four pairs of walking legs Arachnids Arthropods: Advent of Jointed Appendages • Crustaceans belong to the subphylum Crustacea and comprise a diverse group of mandibulates there a 35,000 species of crustaceans described including species of crabs, shrimps, lobsters, crayfish, water fleas, pillbugs, and sowbugs most crustaceans have two pairs of antennae, three pairs of chewing appendages, and various numbers of legs Body of a lobster, Homarus americanus Arthropods: Advent of Jointed Appendages • Millipedes and centipedes have bodies that consist of a head region followed by numerous similar segments centipedes have one pair of legs per segment while millipedes have two centipedes are all carnivorous while millipedes are herbivorous Arthropods: Advent of Jointed Appendages • Insects belong to the Class Insecta and are the largest group of arthropods they are the most abundant eukaryotes on the earth • Insects have three body sections head thorax abdomen Echinoderms: The First Deuterostomes • Echinoderms are deuterostomes that belong to the phylum Echinodermata “spiny skin” and refers to the endoskeleton of calciumrich ossicles just beneath the echinoderm’s skin sea stars, sea urchins, sand dollars, and sea cucumbers all are bilaterally symmetrical as larvae but become radially symmetrical as adults Echinoderms: The First Deuterostomes • A key adaptation of echinoderms is the water vascular system that aids movement from each radial canal, tiny vessels extend through short side branches into thousands of tiny, hollow tube feet Echinoderms can extend the tube feet, attach them to the ocean floor, and pull against them to move • Most echinoderms reproduce sexually but asexual regeneration is also common Chordates: Improving the Skeleton • Chordates are deuterostome that belong to the phylum Chordata they exhibit a truly internal endoskeleton with muscles attached to an internal rod, called a notochord this innovation opened the door to large body sizes not possible in earlier animal forms Chordates: Improving the Skeleton • The approximately 56,000 species of chordates share four principal features notochord nerve cord pharyngeal pouches postanal tail Chordates: Improving the Skeleton • Not all chordates are vertebrates tunicates and lancelets are chordates Chordates: Improving the Skeleton • Vertebrate chordates differ from tunicates and lancelets in two important respects vertebrates have a backbone • this replaces the role of the notochord vertebrates have a distinct and welldifferentiated head A mouse embryo