Chapters 32,33,34

1. Chapters 32,33,34 INTRODUCTION TO ANIMAL EVOLUTION AND DIVERSITY

2. Kingdom: ANIMALIA Characteristics Multicellular Heterotrophic – most ingest organic “food” Lack cell walls, but structural proteins like collagen hold the multicellular bodies together along with intercellular junctions Nervous and Muscle tissuefor impulse conduction and movement Mostly sexual reproduction(although Porifera and Cnidaria can “bud”) Diploid somatic cells and haploid gametes Parazoa lack true tissues (like porifera) or eumetozoa possess true tissues Digestive tracts(internal digestion) Radial / Bilateral symmetry Radial / Spiral Cleavage Protostomes / Deuterostomes Coelomates/Pseudocoelomates/Acoelomates More that 35 phyla

4. The diploid zygote undergoes cleavage – a succession of mitotic divisions This forms a hollow, multicellular ball called the blastula The process of gastrulation follows next, during which layers of embryonic tissues begin to migrate and become germ layers: Ectoderm – covers the surface of the embryo and will give rise to the animal’s outer covering Mesoderm – the germ layer between the ectoderm and the deepest layer the endoderm. It gives rise to the musculature Endoderm – the innermost germ layer, it gives rise to the digestive tract. Animals that have no true germ layers are called parazoa(like Porifera or sponges) Animals that have true germ layers – either 2 (diploblastic) or 3 (triploblastic)layers, are called eumetozoa(all other animals) Animal Development

5. Early Embryonic Development Archenteron

7. Bilateral symmetry is a characteristic of multicellular organisms, particularly animals. A bilaterally symmetric organism is one that is symmetric about a plane running from its frontal end to its caudal end (head to tail), and has nearly identical right and left halves. Most animals are bilaterally symmetric, including humans. They are collectively called the bilateria. The exceptions are sponges (no symmetry), jellyfish and ctenophores or comb jellies (radial symmetry), and echinoderms (partial radial symmetry; starfish exhibit pentamerism). Radial Symmetry is exhibited by organisms that have a dorsal and ventral axis (top and bottom) or an oral and aboral side but no anterior or posterior axis. These animals are collectively called radiata. Pentamerism is a unique body symmetry exhibited primarily by starfish. The body arranged around the axis of the mouth with five equal sectors. Radial vs. Bilateral symmetry

8. Radial symmetry • In biology, radial symmetry is a property of some multicellular organisms. Any cut through the center of a radially symmetric organism, with the plane of the cut going from the top to the bottom (dorsal to ventral), results in roughly equal halves in terms of organs and body parts. For example, multi-layered circular pies exhibit radial symmetry. • Organisms with radial symmetry only have a single orientation: dorsal-ventral (or anterior-posterior, there is no differentiation). Organisms with bilateral symmetry, on the other hand, have two orientations: dorsal-ventral, as well as anterior-posterior. Cnidaria and ctenophores are the only animals with true radial symmetry; echinoderms have partial radial symmetry.

9. Radial vs. Bilateral Symmetry

10. How many germ layers? • The Radiata are diploblastic, whereas • All other eumetozoa are triploblastic

11. Spiral and Determinate Cleavage • Spiral cleavage is a cleavage pattern characteristic of such invertebratesas annelids and mollusks, in which the cleavage planes are oriented obliquely to the polar axis of the oocyte. • Determinate cleavage is when the fate of each embryonic cell is determined very early. If cells are removed during early embryogenesis, the embryo is inviable.

12. Radial and Indeterminate Cleavage • Radial cleavage is a cleavage pattern characteristic of vertebrates and echinoderms, in which the spindle axes are parallel or at right angles to the polar axis of the oocyte. • Indeterminate cleavage is when each cell produced by cleavage, retains the capacity to develop into a complete embryo.

13. Protostomes vs. Deuterostomes Protostomes have the formation of the "mouth first" (hence the name) during gastrulation, before the future anus. (The site of gastrulation initiation, the blastopore, becomes the mouth.) Major protostome phyla include molluscs, annelids and arthropods. Deuterostomes have the formation of the "mouth second" (hence the name) during gastrulation, after the future anus, which is comes from the blastopore, the site of gastrulation initiation. (Contrast with protostomes)

14. A Coelom is the cavity within the body of all “higher” animals and certain primitive worms, formed by the splitting of the embryonic mesoderm into two layers. In mammals it forms the peritoneal (abdomen), pleural (Lung), and pericardial (Heart) cavities. Also called body cavity. Animals can be acoelomates, pseudocoelomates or coelomates. Coelom formation can be schizocoelous or enterocoelous - in schizocoelous organisms, solid “chunks” of mesoderm split and form the coelom - in enterocoelous organisms, certain cells of the archenteron form the mesoderm which migrates and forms the coelom (chordates and echinoderms) Acoelomates, Pseudocoelomates and Coelomates

15. What is a Coelom? A body cavity that forms when the mesoderm layer splits in two – usually found only in echinoderms and chordates.

17. Evolutionary Trends The animal kingdom is monophyletic, meaning if we could trace all animal lineages back to their origin, they would lead to a common ancestor.

18. Summary of Evolutionary Trends

19. Segmentation • Another evolutionary trend, which first appears in the phylum annelida is apparent in other complex phyla, especially chordates

20. THE INVERTEBRATES PARAZOA (lacking true tissues)

21. Phylum Porifera (Sponges) Simplest multicellular animals Porous Filter feeders – water drawn into a central cavity called the spongocoel and then flows out an opening called the osculum. Cells called choanocytes line the osculum. They trap and ingest food particles that pass through the osculum, by phagocytosis. Sessile Hermaphrodites Can reproduce sexually, or by budding

22. THE INVERTEBRATES RADIATA (Radial symmetry)

23. Phylum Cnidaria (Jellyfish, sea anemones, hydras, corals) diploblastic All aquatic (marine) 2 body forms, medusa (mobile) and polyp (sessile) Single opening to the gastrovascular cavity acts as mouth and anus 3 classes in this phylum: Class Hydrozoa, Class Scyphozoa, Class Anthozoa Cells called cnidocytes contain unique organelles called cnidae and together they work to defend the animal or to capture prey. Cnidae called nematocysts are stinging structures

25. Phylum Cnidaria, cont’d. • Class Hydrozoa – related to jelly fish. They alternate between the sessile polyp stage and the mobile medusa (reproductive) stage. Hydras however, exist only as polyps

26. Phylum Cnidaria, cont’d. Australia's box jelly is the most dangerous jellyfish. Its toxin is more potent than cobra venom and can kill a person in minutes. • Class Scyphozoa – The common jelly fish. The predominant life stage is the medusa (polyp stage usually missing) • Class Anthozoa (sea flowers) – the sea anemones and corals, predominant stage is the polyp – sessile.

27. Phylum Ctenophora (Comb Jellies) • Named for the 8 combs of cilia used for locomotion • Most comb jellies also have one pair of long tentacles used for trapping and ingesting prey

28. THE INVERTEBRATES ACOELOMATES

29. Marine Flatworm Phylum Platyhelminthes (Flatworms) tapeworms, planarians, flukes, Dorsoventrally flat, unsegmented Many parasitic Mouth, no anus Aquatic (Ponds, Lakes, Class Turbellaria (Planarians) • Free-living, nonparasitic carnivores • Pond-dwelling • Can regenerate tissues Class Trematoda (Flukes) • Animal parasites like the schistosome (natural host is a pond snail) Class Cestoidea • Tapeworms – live mostly in the intestines of vertebrates including humans

30. THE INVERTEBRATES PSEUDOCOELOMATES

31. Phylum Rotifera (Rotifers) Multicellular, microscopic Extremely small ~ 1000 cells Aquatic, mostly fresh water Transparent bodies with visible organs Unusual reproduction known as parthenogenesis (some species consist of only females, that can develop from unfertilized eggs). Other species produce both males and females by parthenogenesis

32. Phylum Nematoda (Roundworms) Unsegmented, round worms such as C. elegans Hookworms, stomach worms Very small Parasitic like Trichinella spiralis which causes trichinosis in humans that ingest uncooked pork – causes cysts in organs including the brain Live in damp soil, water Usually sexual reproduction

33. THE INVERTEBRATES COELOMATES - PROTOSTOMES

34. Chiton Giant Squid Class: Polyplacophora Class: Gastropoda Class: Bivalvia Class: Cephalopoda Phylum Mollusca (snails, slugs, squids, octopi, clams, mussels) Squid, snails, clams, chitons Unsegmented, soft bodies Aquatic (possess gills) and terrestrial Muscular foot, Mouth, tongue (radula), a visceral mass and a mantle or covering that secretes the shell

36. Phylum Annelida (Earthworms, Leeches) Cylindrical, segmented bodies that have bristles called chaetae, made of chitin Some have appendages called parapodia which they use to move with Others move with a hydrostatic skeleton Leech – Class Hirudinea Earthworm – Class Oligochaeta

37. Class Diplopoda (millipedes) Class: Insecta Class: Chilopoda Class: Crustacea Phylum Arthropoda (jointed appendages) Exoskeletons made of chitin Growth in stages after molting, some undergo either complete or incomplete metamorphosis Jointed appendages True coeloms Segmented bodies Open circulatory system Most have compound eyes Heart on dorsal side of body

40. Incomplete Metamorphosis in Insects Adults do not look very different from the young – only bigger The immature insect undergoes a series of molts as it grows bigger

41. Complete Metamorphosis in Insects The larval stage is specialized for eating – called maggots, grubs, or caterpillars. Metamorphosis from larval to adult stage occurs during pupal stage – takes place in a cocoon or chrysalis.

42. More Arthropods! Class Arachnida Scorpions, ticks, spiders, mites Trilobites are an extinct subgroup of the Phylum Arthropoda

43. THE INVERTEBRATES COELOMATES - DEUTEROSTOMES

44. Phylum Echinodermata Star fish, Sea cucumbers, sand dollars, sea urchins Unsegmented Rigid body wall Ventral mouth, dorsal anus Marine External fertilization Separate male and female organisms

45. THE CHORDATES INVERTEBRATE AND VERTEBRATE CHORDATES

46. Deuterostomes Segmented Coelomates Four chordate features: A notocord A dorsal, hollow nerve cord Pharyngeal slits A muscular postnatal tail This phylum actually contains 3 sub-phyla Sub-phylum Urochordata Sub-phylum Cephalochordata Sub-phylum Vertebrata or Craniata } These 2 sub-phyla are invertebrates Phylum Chordata

47. Chordate Characteristics

48. Chordate Characteristics, cont’d. • A Notocord is a flexible rod made up of fluid-filled cells encased in a stiff, fibrous tissue. It offers skeletal support – it is present in ALL chordate embryos. It persists in adult invertebrate chordates, but disappears in most adult vertebrates, leaving behind remnants in the form of gelatinous discs between vertebrae 2. Dorsal, hollow nerve cord – develops from the ectoderm and is located dorsal to the notochord – this will develop into the adult brain and spinal cord. Remember: in many lower animals like the arthropods, the nerve cord is ventrally located. 3. Pharyngeal slits – slits located just posterior to the mouth, in a region called the pharynx. These slits allow water to enter and leave, without entering the digestive system. In invertebrate chordates, they act as filter-feeding mechanisms. In aquatic vertebrates, they become the gills for gas exchange and in terrestrial vertebrates, they develop into parts of the lower jaw and inner ear. 4. Muscular, Postnatal tail – extends posterior to the anus – is lost in higher primates and humans (the coccyx is a remnant of this tail)

49. INVERTEBRATE CHORDATES

50. Sub-Phylum Urochordata (Sea squirts) - commonly called Tunicates or sea quirts - some are sessile marine animals others are planktonic - the adult lacks the notochord and tail, but has the pharyngeal slits to link it to other chordates - a tunic of cellulose-like carbohydrate earns it its common name