What is an Animal?

1. What is an Animal? Chapter 25 TURBO BLAST

2. Why are animals classified as one kingdom? • All animals are: • Eukaryotic, multicellular • Able to move in specific ways to obtain food, reproduce, and protect themselves • Most animals: • Have specialized cells/tissues (that form organs)

3. How do animals obtain food? • All animals are heterotrophic (must eat other organisms for food) • Depend either directly or indirectly on autotrophs for food • Animals hypothetically evolved in water (recall what cells require for all biochemistry) • Some animals living in water do not move from place to place, must filter food from water • Organisms that permanently attach to a surface are called sessile • This is not possible for land animals— there is very little suspended food in the air • Land animals need to use more oxygen and energy to find food

4. How do animals digest food? Animals must ingest (take in) food • Once ingested, food must be digested • Some animals digest food within special cells • Other animals have a special internal digestion cavity • Food is not always available for animals; when an animal encounters excess food, it can be stored as fat or glycogen to use as fuel when food is not available • Ex: Flatworms (planarian) have only one opening to their digestive tract, called a pharynx • Ex: Earthworms have a mouth (entrance) at one end and an anus (exit) at the other end of the tract

5. What are the functions of some animal cells? • Most animal cells are specialized to carry out different functions • Sensing food • Finding mates • Identify predators/protect themselves • Light reception • Homeostasis • Movement

6. Development and Fertilization • Most animals reproduce sexually (males produce sperm, females produce eggs) • Some animals do reproduce asexually • Most animals develop from a fertilized egg cell called a zygote • Sperm (n) + egg (n) = zygote (2n) • Fertilization may be internal or external for different species • After fertilization the development of different animal species all have similar, genetially determined stages of development

7. Embryonic Development • The zygote (single fertilized cell) divides by mitosis and cell division to form two cells • This process is called cleavage • Once cell division has occurred, the organism is known as an embryo A: zygote B: two cells C: four cells D: 8 cells E: continued cell divisions… F: cell-covered, fluid-filled ball called a blastula *blastula is formed early in development

8. Gastrulation • After blastula is formed, cell division continues • Cells from one side of blastula move inward to form a gastrula • Gastrula: structure made up of two layers of cells with an opening at one end (Picture how a potter might make a bowl from a round ball of clay) • Layer of cells on outer surface of gastrula is called the ectoderm– eventually becomes skin and nervous tissue • Layer of cells lining inner surface of gastrula is called the endoderm—eventually becomes digestive tract

9. How is the mesoderm formed? • In some animals, development of the gastrula progresses until a layer of cells called the mesoderm forms • Mesoderm is the third cell layer found in developing embryo, found between endoderm and ectoderm—eventually becomes muscles, circulatory, excretory, and respiratory systems

10. Which came first: the mouth or the anus? • When the opening in the gastrula develops into the mouth, the animal is a protostome • (proto = first; stoma = mouth) • Ex: snails, earthworms, insects • When the opening in the gastrula develops into the anus first, the animal is a deuterostome • (deutero = second; stoma = mouth) • Ex: starfish, fish, amphibians, birds, reptiles, and you • Scientists hypothesize that protostomes appeared first in evolutionary history, followed by deuterostomes • Determining if an animal is a protostome or deuterostome can help biologists identify its phylogeny

11. What changes occur during growth an development? • Embryonic development of animals holds clues to animal evolutionary history • Cells in developing embryos continue to differentiate and become specialized to perform different functions • Most animal embryos develop into juveniles (look like smaller versions of the adult) • In some animals (insects, echinoderms), the embryo develops inside an egg into a intermediate stage called a larva—usually doesn’t look like the adult • Sessile animals usually have free-moving larvae • Larvae continue to grow into juveniles, then to adults

13. Body Plans and Adaptations • Animal body structure is related to how the animal moves around during its lifetime • Symmetry – describes how an animal’s body structures are arranged • Asymmetry—no line can divide into two equal halves • The bodies of most sponges consist of two layers of cells (no formation of endoderm, mesoderm, or gastrula)

15. Body Symmetry Relates to Animal Movement • Radial symmetry can be divided along any plane through a central axis into roughly equal halves (allows animals to move in 360⁰ and detect and capture prey from any direction) • Animals with radial symmetry include: hydras, jellyfish, starfish, sea anemone, coral, sand dollars • Animals with radial symmetry have muscle movement controlled by a neural net

16. Body Symmetry Relates to Animal Movement • Bilateral Symmetry - can be divided down the animal’s length into similar right and left halves • Animals with bilateral symmetry move forward, have more coordinated movement • Anterior or head end has sensory organs (vision, olfactory, auditory) and a central nervous system • Posterior is the tail end • Dorsal is the upper surface, which looks different from the Ventral or lower surface

17. Bilaterally Symmetrical Animals All Develop from Three Embryonic Layers • Recall the ectoderm, mesoderm, and endoderm cell layers - these give rise to specialized regions in animal body plans • Some bilaterally symm. Animals also have a fluid-filled cavity called a coelom (coel = “cavity”) that provides internal support for movement • Animals that lack a coelom are acoelomates • Animals that have a coelom partially covered in mesoderm are pseudocoelomates • Animals with a coelom surrounded by mesoderm are coelomates

18. A coelom acts as leverage for muscle contractions • Think of the rigidity of a very-full water balloon • Leads to flexibility of the organism (bending from side to side, squeezing in sections, etc.) • Acoelomates may have been the first organisms to evolve • Have a digestive tract that extends throughout the body • Organs are embedded in the solid tissues of the body • Pseudocoelomates have more complex movement • Also have a one-way digestive tract (mouth, middle section for food breakdown/absorption, anus) • Coelomates have the greatest diversity • Specialized organs and organ systems develop in the coelom (which cushions organs and allows them to grow & move within body cavity)

19. Body cavities led to greater animal diversity • As animals diversified, they adapted to life in different environments • Some (like mollusks) developed hard shells to protect soft bodies • Some developed hardened internal support, such as spicules (like sponges) • Some developed exoskeletons – hard coverings on the outside of the body that provide a framework, protect soft tissues, prevent water loss, and provide protection from predators • These are rigid and must be shed for the animal to grow larger • Exoskeletons are often possessed by invertebrates, animals that lack a spine (ex: crabs, beetles, spiders) • Some developed endoskeletons – internal skeletons that protect internal organs and provide brace for muscles • Endoskeletons are made of calcium carbonate, cartilage, or bone • (Starfish are invertebrates with endoskeletons, while fish, reptiles, amphibians, birds and mammals are vertebrates)

20. A vertebrate is an animal with an endoskeleton and a backbone (spine) • All are bilaterally symmetrical Invertebrate Invertebrate with Endoskeleton Invertebrate with Spicules Invertebrate with Exoskeleton Vertebrates with Endoskeleton and Spine

21. Animal Origins • Animals likely evolved from aquatic, colonial protists • Traced back to late Precambrian fossil records • Bilateral symmetry appears much later, but all body plans that exist today were present by the Cambrian Period 543 million years ago • These different body plans have diversified since then, but no new body plans have arisen (based on fossil evidence)