Animals

What is an animal?

§ A blastula is an embryonic stage that marks the end of cleavage during animal development; a hollow ball of cells.

§ A gastrula is an embryonic stage resulting from gastrulation in animal development.

§ A larva is an immature individual that is structurally and often ecologically very different from an adult.

§ Metamorphosis is the transformation of a larva into an adult.

Invertebrates

Sponges have relatively simple, porous bodies

§ Porifera is the phylum that contains the sponges, characterized by choanocytes, a porous body wall, and no true tissues.

§ Radial symmetry is an arrangement of the body parts of an organism like pieces of a pie around an imaginary central axis.

§ An ameobocyte is an amoeba-like cell that moves by pseudopodia, found in most animals; may digest and distribute food, dispose of wastes, make skeleton, fight infections, and change into other cell types.

§ A choanocyte is a flagellated feeding cell found in sponges; also called a collar cell.

§ A choanoflagellate is an ancestral colonial protist from which sponges, and possibly all animals, probably arose.

Cnidarians are radial animals with stinging threads

§ Cnidaria is the phylum that contains the hydras, jellyfish, sea anemones, corals, and related animals characterized by cnidocytes, radial symmetry, a gastrovascular cavity, polyps and medusae.

§ A polyp is one of two types of cnidarian body forms; a columnar, hydra-like body.

§ A medusa is one of two types of cnidarian body forms; an umbrella-like body form.

§ A gastrovascular cavity is a digestive compartment with a single opening, the mouth.

§ A cnidocyte is a specialized cell for which the phylum Cnidaria is named; consists of a capsule containing a fine coiled thread, which, when discharged, functions in defense and prey capture.

Most animals are bilaterally symmetrical

§ Bilateral symmetry is an arrangement of body parts such that an organism can be divided equally by a single cut passing longitudinally through it.

§ Anterior refers to the front, or head, of a bilaterally symmetrical animal.

§ Posterior refers to the rear, or tail, of a bilaterally symmetrical animal.

§ Dorsal refers to the back of a bilaterally symmetrical animal.

§ Ventral refers to the underside, or bottom, of a bilaterally symmetrical animal.

§ Lateral refers to the side of a bilaterally symmetrical animal.

Flatworms are the simplest bilateral animals

§ Platyhelminthes is the phylum that contains the flatworms, the bilateral animals with a thin, flat body form, gastrovascular cavity or no digestive system, and no body cavity.

§ Free-living flatworms are represented by Planarian, a non-parasitic flatworm.

§ A fluke is one of a group of parasitic flatworms.

§ A tapeworm is a parasitic flatworm characterized by the absence of a digestive tract.

Most animals have a body cavity

§ A body cavity is a fluid-containing space between the digestive tract and the body wall.

§ A pseudocoelom is a body cavity that is in direct contact with the wall of the digestive tract.

§ A coelom is a body cavity completely lined with mesoderm.

Roundworms have a pseudocoelom and a complete digestive tract

§ Nematoda is the phylum that contains the roundworms, or nematodes; characterized by a pseudocoelom, a cylindrical, wormlike body form, and a tough cuticle.

§ A cuticle is a tough, nonliving outer layer of the skin.

Diverse mollusks are variations on a common body plan

§ Mollusca is the phylum that contains the mollusks; characterized by a muscular foot, mantle, mantle cavity, and radula.

§ The molluscan foot is a muscular organ that functions in locomotion.

§ In a mollusk, the mantle is the outgrowth of the body surface the drapes over the animal.

§ A radula is a toothed, rasping organ used to scrape up or shred food.

§ A gastropod is a member of the largest group of mollusks, including snails and slugs.

§ A bivalve is a member of a group of mollusks that includes the clams, mussels, scallops, and oysters.

§ A cephalopod is a member of a group of mollusks that includes squids and octopuses.

Most animals have segmented bodies

§ Segmentation is subdivision along the length of an animal body into a series of repeated parts called segments.

Earthworms and other annelids are segmented worms

§ Annelida is the phylum that contains the segmented worms, or annelids; characterized by uniformed segmentation; includes earthworms, polychaetes, and leeches.

§ An earthworm is one of three large groups of annelids, that eats its way through the soil, extracting nutrients as soil passes through its digestive tube.

§ Polychaetes are the largest group of annelids, characterized by segmental appendages and hard bristles that project from them.

§ Leeches are the third largest group of annelids, characterized by parasitic, blood-sucking forms, and free-living carnivores that eat small invertebrates.

Arthropods are the most numerous and widespread of all animals

§ Arthropoda is the most diverse phylum in the animal kingdom, characterized by a chitinous exoskeleton, molting, jointed appendages, and a body formed of distinct groups of segments; includes the horseshoe crab, arachnids, crustaceans, millipedes, centipedes, and insects.

§ An exoskeleton is a hard, external skeleton that protects an animal and provides points of attachment for muscles.

§ Molting is the process of shedding an old exoskeleton and secreting a new, larger one.

§ The horseshoe crab is a “living fossil”; a member of a group of spider-like arthropods that were abundant in the sea about 300 million years ago.

§ An arachnid is a member of a major arthropod group that includes spiders, scorpions, ticks, and mites; characterized by 4 pairs of appendages.

§ A crustacean is a member of a major arthropod group that includes lobsters, crayfish, crabs, shrimps, and barnacles.

§ A millipede is a scavenging, herbivorous arthropod with similar, repeating segments over the body, and 2 pairs of short legs per body segment.

§ A centipede is a carnivorous arthropod with similar, repeating segments over the body, and 1 pair of long legs per body segment.

Insects are the most diverse group of organisms

§ Insects have a three-part body consisting of a head, a thorax, and an abdomen.

§ Most adult insects have three pairs of legs, and one or two pairs of wings.

§ Some insects undergo incomplete metamorphosis, in which the young resemble adults by are smaller with different body proportions.

§ Other insects undergo complete metamorphosis, in which their larval stages are specialized for eating and growing , and look different from the adults.

Echinoderms have a spiny skin, endoskeleton, and a water vascular system

§ Echinodermata is the phylum of echinoderms, including sea stars, sea urchins, and sand dollars; characterized by a rough or spiny skin, a water vascular system, an endoskeleton, and radial symmetry in adults.

§ An endoskeleton is a hard skeleton located within the soft tissues of an animal.

§ The water vascular system is a radially arranged system of water-filled canals that branch into extensions called tube feet.

Chordates

Our own phylum, Chordata, is distinguished by four features

§ Chordata is the phylum of the chordates; characterized by a dorsal hollow nerve cord, a notochord, gill structures, and a post-anal tail; includes lancelets, tunicates, and vertebrates.

§ A nerve cord is an elongated bundle of axons and dendrites, usually extending longitudinally from the brain or anterior ganglia.

§ A notocord is a flexible, cartilage-like, longitudinal rod located between the digestive tract and nerve cord in chordate animals.

§ The gill structure is composed of gill slits and the structures supporting them.

§ A post-anal tail is a tail posterior to the anus.

§ A vertebrate is a chordate animal with a backbone; includes agnathans, cartilaginous fishes, bony fishes, amphibians, reptiles, birds, and mammals.

§ A tunicate is one of a group of invertebrate chordates; also known as a “sea squirt”.

§ A lancelet is one of a group of invertebrate chordates; has a blade-like shape.

A skull and a backbone are hallmarks of vertebrates

§ A skull is one of the distinguishing features of a vertebrate; a bony structure that protects the brain.

§ A backbone is a series of segmental units called vertebrae, present in all vertebrates.

§ A vertebra is one of a series of segmented units making up the backbone of a vertebrate animal

Most vertebrates have hinged jaws

§ Agnatha is a class of vertebrate animals that are superficially fishlike but lack a jaw and paired fins.

Fishes are jawed vertebrates with gills and paired fins

§ Chondrichthyes is a class of cartilaginous fishes that includes sharks, rays, and skates.

§ Osteichthyes is the vertebrate class of bony fishes, which includes trout, goldfish, and all other varieties of fishes.

§ Cartilaginous fishes have a flexible skeleton made of cartilage, which includes members of the class Chondrichthyes.

§ The lateral line system is a row of sensory organs along each side of fish’s body; it enables a fish to detect minor vibrations in the water.

§ Bony fishes have a stiff skeleton reinforced by hard calcium salts.

§ An operculum is a protective flap on each side of fish’s head that covers a chamber housing the gills.

§ A swim bladder is a gas-filled internal sac that helps bony fish maintain buoyancy.

§ A ray-finned fish is a bony fish having fins supported by thin, flexible skeletal rays.

§ A lobe-finned fish is a bony fish with strong, muscular fins supported by bones; lobefins are extinct except for one species, the coelacanth.

Amphibians were the first land vertebrates

§ Amphibia is a class of vertebrate animals that consists of the amphibians; such as frogs, toads, and salamanders.

Reptiles have more terrestrial adaptations than amphibians

§ Reptilia is a class of vertebrate animals that consists of the reptiles, including snakes, lizards, turtles, crocodiles, and alligators.

§ An amniotic egg is a shelled egg in which an embryo develops within a fluid-filled amniotic sac and is nourished by yolk.

§ Absorbing external heat rather than generating it internally is called ectothermic.

§ Using heat generated by metabolism to maintain a warm, a constant body temperature is called endothermic.

Birds share many features with their reptilian ancestors

§ Aves is a class of endothermic vertebrate animals that consists of the birds; distinguished by feathers.

Mammals also evolved from reptiles

§ Mammalia is a class of endothermic vertebrate animals that consists of the mammals; distinguished by hair and mammary glands.

§ A monotreme is an egg-laying mammal, such as a duck-billed platypus.

§ A marsupial is a pouched mammal, such as a kangaroo, opossum, or koala.

§ A marsupium is the external pouch on the abdomen of a female marsupial.

§ Placental mammals complete their embryonic development in the uterus, nourished via the mother’s blood vessels in the placenta.

A phylogenetic tree gives animal diversity an evolutionary perspective

§ A protostome is an animal with a coelom that develops from solid masses of cell that arise between the digestive tube and the body wall of the embryo; includes the mollusks, annelids, and arthropods.

§ A deuterostome is an animal with a coelom that develops from hollow outgrowths of the digestive tube of the early embryo; includes the echinoderms and the chordates.