23.1 What Is an Animal?

What Is an Animal? Only animals pass through a blastula stage in embryonic development. Blastula: a hollow, fluid-filled ball of cells that forms once an egg is fertilized by sperm

What Is an Animal? All animals are: Multicelled Heterotrophs (they cannot make their own food) Composed of cells that do not have cell walls

23.2 Lessons from the Animal Family Tree

Animal Family Tree Figure 23.2 Porifera Cnidaria Platyhelminthes Annelida Mollusca Nematoda Arthropoda Echinodermata Chordata (sponges) (flatworms) (roundworms) bilateral symmetry tissues symmetry ancestral protist Figure 23.2

Animal Family Tree Except for the sponges in Porifera, the members of all the phyla have bodies composed of tissues. Except for Porifera and Cnidaria, all phyla reviewed exhibit bilateral symmetry. Cnidaria exhibits radial symmetry Porifera exhibits no symmetry

Symmetry (a) Radial symmetry: Symmetry around a central point (b) Asymmetry: No planes of symmetry (c) Bilateral symmetry: Symmetry across the sagittal plane sagittal plane Figure 23.3

Animal Family Tree The members of all phyla reviewed other than Porifera Cnidaria Platyhelminthes Posess a central body cavity known as a coelom.

of uninterrupted tissue. tissue from exterior to gut gut (digestive tract) flatworm No coelom. Phylum Platyhelminthes, composed of flatworms, is one of the phyla that has no coelom. Note that from its gut to its exterior, the flatworm is composed of uninterrupted tissue. coelom gut (digestive tract) earthworm Coelom. The earthworm is one of many animals that has a coelom — a fluid-filled central cavity that usually surrounds the gut. Figure 23.4

23.3 Across the Animal Kingdom: Nine Phyla

Sponges Phylum Porifera’s sponges live by drawing water into themselves through a series of tiny pores on their exterior and then filtering the food from this water while extracting oxygen from it.

Sponges Asculum Inner cells with flagella create currents. The currents cause water to flow into pores and out the osculum at top. Figure 23.5

Jellyfish Phylum Cnidaria (jellyfish, sea anemones, hydras, and reef-building coral animals) use stinging tentacles to capture prey Many cnidarians have two stages of life Adult, medusa stage of life: swims in the water Immature polyp stage of life: remains fixed to a solid surface.

Cnidarians medusa mesoglea gastrovascular cavity tentacles mouth mouth polyp Figure 23.6

Flatworms Phylum Platyhelminthes (flatworms) contains mostly small creatures, dwelling either in aquatic or moist terrestrial environments. Flatworms have bilateral symmetry and organs, but have no coelom or system of blood circulation.

Flatworm Figure 23.7

Worms The worms of phylum Annelida provide a clear example of body sementation. Most annelids are marine, and some are freshwater. Common earthworms are terrestrial.

Annelid Diversity Figure 23.9

Molluscs Three important classes of phylum Mollusca Gastropods (snails, slugs) Bivalves (oysters, clams, mussels) Cephalopods (octopus, squid, nautilus) All molluscs posess a fold of skin-like tissue called a mantle that usually secretes material that forms a shell.

Body Plan of a Mollusc heart mantle gill shell anus stomach tooth covered radula mantle cavity mouth foot mouth Figure 23.10

Roundworms The mostly microscopic roundworms of phylum Nematoda exist in enormous numbers in all kinds of habitats on Earth A number of roundworms are agricultural pests and some are human parasites

Roundworms Figure 23.11

Arthropods Contains three subphyla: Uniramia (millipedes, centipedes, insects) Chelicerata (spiders, ticks, mites, horseshoe crabs) Crustacea (shrimp, lobsters, crabs, barnacles) All arthropods have the following characteristics: An exoskeleton Paired, jointed appendages All molt

Arthropod Features head thorax abdomen exoskeleton muscles joint segments Figure 23.12

Echinoderms All members of phylum Echinodermata (sea stars, sea urchins, sea cucumbers) are marine. All inhabit the ocean floor.

Sea Star Echinoderms Figure 23.13

Chordates Contains three subphyla: Vertebrata (includes all vertebrates) Cephalochordata (lancelets) Urochordata (includes tunicates and sea squirts) Only the vertebrates have a vertebral column All posess the following at some point in their lives: Notochord Nerve cord on the dorsal side Post-anal tail Series of pharyngeal slits

Four Universal Chordate Features notochord dorsal nerve cord post-anal tail pharyngeal slits anus Figure 23.15

23.4 Animal Reproduction

Sexual Reproduction Entails the fusion of eggs and sperm from two individuals (asexual reproduction does not) Members of the less complex animal phyla commonly reproduce both sexually and asexually. Sexual reproduction is the norm with more complex animals, although asexual reproduction is sometimes seen.

Asexual Reproduction Forms of asexual reproduction include: Budding Fission Parthogenesis

Sexual and Asexual Reproducer reproductive polyp female medusa medusa buds male medusa feeding polyps egg sperm zygote larva blastula polyp from budding polyp Figure 23.17

Hermaphrodites Sexual Reproduction can be practiced by hermaphrodites. Some animals change sex over the course of their lifetimes.

23.5 Egg Fertilization and Protection

Egg Fertilization and Protection In animals, eggs and sperm are brought together and eggs are protected following fertilization in a number of ways. Primitive ancestral method: parents broadcast both eggs and sperm into an aquatic environment and provide no subsequent care for the eggs that become fertilized.

Egg Fertilization and Protection With movement up the scale of animal complexity, species tend to produce fewer eggs, to exhibit more directed means of bringing these eggs together with sperm, and to provide greater protection to the fertilized eggs that result.

Egg Fertilization and Protection female male egg mature frog fertilized egg sperm immature frog developing embryo tadpole Figure 23.21

Fertilization Can be external or internal Only some species that employ internal fertilization also employ copulation. Other species rely on females to insert spermatophores into their own reproductive tracts.

Protection Vertebrate evolution resulted in a range of strategies for protecting fertilized eggs and the offspring that develop from them. Reptile evolution resulted in the amniotic shell, whose shell and system of membranes allows it to be laid in dry environments Mammalian evolution produced the placental system, in which fertilized eggs develop inside a mother’s body.

23.6 Organs and Circulation

Organs and Circulation Organs are complex bodily structures composed of several types of tissues. They are found in all of the animal phyla except Porifera and Cnidaria

Organs and Circulation Vertebrates have closed circulation systems. Arthropods and small molluscs have open circulation systems.

23.7 Skeletons and Molting

Skeletons and Molting Three kinds of skeletons are found in animals Endoskeletons Exoskeletons Hydrostatic skeletons To continue their growth, animals with exoskeletons must periodically molt.

Table 23.1 Animal Phyla Table 23.1 Phylum Members include Live in Characteristics Porifera Sponges Ocean water (marine), with a few living in freshwater Sessile (fixed in one spot) as adults, no symmetry. System of pores through which water flows serves to capture nutrients. Bodies do not have organs or true tissues. Sexual and asexual reproduction Cnidaria Jellyfish, hydrozoans, sea anemones, coral animals Almost all marine; a few in freshwater Radial symmetry, medusa (swimming) and polyp (largely sessile) stages of life. Use stinging tentacles to capture prey. Have tissues. Can reproduce sexually or by budding. Platyhelminthes Flatworms (including flukes, tapeworms) Marine, freshwater, or moist terrestrial environments Bilateral symmetry, hermaphroditic, possess organs, no central cavity. Many are parasites. Can reproduce through fission. Annelida Segmented worms Most are marine, some freshwater and moist terrestrial Distinct body segmentation in varieties such as earthworms. Leeches are annelids. Mollusca Gastropods (snails, slugs), bivalves (oysters, clams, mussels), cephalopods (octopus, squid, nautilus) Marine, freshwater, moist terrestrial Mantle that can secrete material that becomes shell; mantle cavity housing gill or lungs. Nematoda Roundworms Almost all environments Small size in most, but some are several meters long. Many are crop pests, other animal parasites. Arthropoda Vast group that includes insects, spiders, mites, crabs, shrimp, and centipedes Many aquatic and terrestrial environments External skeleton; paired, jointed appendages; molting; open circulation system. Echinodermata Sea stars, sea urchins, sea cucumbers Always marine, most on ocean floor Generally have radial symmetry as adults; tube feet in some species, slow ocean floor movement in most. Chordata Vertebrates, lancelets, sea squirts Great variety of aquat- ic and terrestrial envi- ronments At some point, all possess noto- chord, dorsal nerve chord, pharyn- geal slits, post-anal tail. Vertebrates have vertebral column. Table 23.1