Embryology and The Animal Kingdom Holly Morgan Animal

Embryology and The Animal Kingdom Holly Morgan

Animal Basics • Animals are – Multicellular – Heterotrophic – Eukaryotic • They have embryonic layers • Bodies held together by structural protein (collagen) • They have intracellular junctions – Tight junctions – Desmosomes – Gap junctions • They have muscle cells and nerve cells (not seen in other organisms)

Development • Once the sperm fertilizes the egg a diploid zygote is formed • The zygote then undergoes cleavage – Cleavage: mitotic cell division without cell growth • After cleavage a blastula is formed. – Blastula: a hollow ball of cells • The blastula then goes through gastrulation – Gastrulation: when layers of embryonic tissues that form the adult body are produced

Development continued • After gastrulation, a gastrula is formed.

Larvae and Metamorphosis • Some animals go through multiple stages of maturation before they become adults. • Many animals have at least one stage: the larval stage – This is a sexually immature form of an animal that is morphologically different from its adult stage • These larvae eventually go through metamorphosis that transforms the organism into an adult.

Symmetry • Radial Symmetry • Bilateral Symmetry • Dorsal (top) vs. Ventral (bottom) • Anterior (head) vs. Posterior (tail) • Cephalization: sensory equipment and central nervous system concentrated around the head

Tissues • Ectoderm: the germ layer that becomes the outer covering of the organism • Endoderm: the innermost germ layer that develops into the archenteron (digestive tube) • Mesoderm: middle layer that forms the muscles • Diploblastic: animals with only two germ layers • Triplosblastic: animals with only three germ layers; all bilaterally symmetrical animals

Body Cavities

Protostome Development vs. Deuterostome Development

ANIMAL PHYLA AND CLASSIFICATIONS

Porifera (aka sponges) • “pore bearer” • Sedentary • Suspension feeders: they caputrue food particles suspended in the water • Choanocytes: flagellated collar cells that trap and ingest food • Amoebocytes: cells that use pseudopodia, help in transport, and produce calcium carbonate skeletal fibers with in the sponge • Hermaphrodites: each individual functions as a male and a female in sexual reproduction

Cnidarians • Sessile and floating • Diploblastic with radial symmetry • Body plan: a gastrovascular cavity with a single opening and tentacles • Polyps: sessile cnidarians with their tentacles facing up • Medusa: floating cnidarians their opening and tentacle facing downward • Carniverous • Cnidocytes: unique cells that help in defense and capturing food. Contain nematocysts, or stinging capsules. • Contractile and nervous tissues in their simplest form

Types of Cnidarians • Hydrozoans – Polyp and medusa forms – Hydra • Scyphozoans – Medusa is predominant stage – Jellyfish • Cubozoans – Box shaped medusa stage • Anthozoans – Polyps – Sea anemones

Platyhelminthes • • • “flat worms” Triploblastic acoelomates Gastrovascular cavity with single opening Some parasitic species Turbellarians – Free living – Mostly marine – Planarians – Asexual reproduction

• Monogenea and Trematodes – Parasitic – Suckers – Well known type of trematodes are flukes • Tapeworms – Parasitic – Live inside many vertebrates – Lack a gastrovascular cavity – Can get ingest them through undercooked meat

Molluscs • Aquatic and terrestrial • Body makeup – Foot: muscular, used for movement – Visceral Mass: contains most of the internal organs – Mantle: a fold of tissue that drapes over the visceral mass and secretes a shell – Mantle Cavity: water filled chamber that houses the gills, anus, and excretory pores – Radula: rasping organ used to scrape up food • Trochophore: cilliated larval stage

Types of Molluscs • Chitons – Oval shaped body – Shell divided into eight unsegmented dorsal plates • Gastropods – Slugs and snails – Torison: visceral mass rotates up to 180 degrees causing the animals’s anus and mantle cavity to end up above its head • Bivavles – Shell divided into two halves that are hinged together – Sessile suspension feeders • Cephalopods – Active predators – Closed circulatory system

Annelids • “Little rings” meaning they are segmented worms • Oligochaetes – Bristles made of chitin – Earthworms – Hermaphrodites that cross fertilize • Polychaetes – Parapodia (almost feet) • Leeches – Parasitic- suck blood – Hirudin: chemical that keeps blood of host from cagulating

Nematodes • Nonsegmented pseudoceolomate • Body covered by a tough coating called a cuticle • Sexually reproduce with internal fertilization • Rounded worms tapered at the end • Trichinella spiralis

Arthropods • “jointed feet” • Hard exoskeleton constructed from protein and polysaccharide chitin – Molting: the shedding of the exoskeleton • Jointed appendages • Earliest type: trilobites • Open circulatory system

• Chelceriforms Types of Arthropods – Claw like feeding appendages called chelicerae – Lack antennae and have simple eyes – Spiders, scorpions, and ticks • Myriapods – – Millipedes and centipedes Terrestrial Large number of legs May have been the earliest animals on land • Insects – – Hexapoda Originated in the Devonian period Metamorphosis Some may fly • Crustaceans – Aquatic – Lobsters and crabs

Echinoderms “spiny skin” Slow moving or sessile Endoskeleton Water vascular system: a network of hydraulic canals branching into extensions called tube feet • Sexual reproduction • Sea stars, sea urchins, sand dollars, sea lilies, sea cucumbers • •

Chordates • Notochord: a longitudinal, flexible rod located between the digestive tube and the nerve cord • Dorsal hollow nerve cord: develops into the central nervous system • Pharyngeal slits: allow water entering the mouth to exit the body, use to function as suspension feeders but have been modified for gas exchange • Muscular post-anal tail: contains skeletal and muscle elements

Tunicates Lancelets

Gnathostomes • Disappeared by the beginning of the Carboniferous period • Placoderms – “plate skinned” – Paired fins and tail allow them to swim efficiently – Jaws • Acanthodians – Devonian period

Chondrichthyans • • • Sharks, rays, , and their relatives “cartilidge fish” Skeleton made of cartilage Lateral line system Spiral valve

Osteichthyes • • • “bony fish” Bony endoskeleton Breathe by gills Operculum: a protective bony flap Swim bladder: air sac that keeps them bouyant Two types – Ray finned: trout, tuna, bass, herring – Lobe finned

Amphibians Tetrapod: four legged with pelvic girdle “Two lives” Early life in water, later life on land Secrete distasteful or poisonous mucus for protection • Frogs, salamanders, and caecilians • •

Reptiles • Tetrapod • Amniote: named for their amniotic eggs which have specialized membranes to protect the embryo • Scales made out of keratin to prevent dehydration on land • Ectothermic: absorption of external heat • Early types: dinosaurs • Types today: turtles, alligators, and lizards

Birds • Derived from reptile • Feathers and wings • Toothless • Acute vision and fine muscle for flight • Amniotic eggs control

Mammals • • • Mammary glands produce milk for offspring Differential teeth Endothermic High metabolic rate Respiratory and circulatory sysems Monotremes – Lay eggs but produce milk • Marsupials – Placenta – Marsupium: maternal pouch where live young finish their development

Eutherians (Placental Mammals) • Complex placenta • Primates – Opposable thumb – Large brain – Shorter jaws – Flat nails rather then claws – Forward looking eyes – Hominoids- apes (chimpanzees and humans)

Humans • Bipedalism • More developed brain – Cognitive thought – Problem solving

Review Questions 1. Name and describe the next stage in embryonic development once the blastula is formed. 2. What is the difference between choanocytes and ameobocytes in a porifera? 3. _____: Annelid: : Fluke: Platyhelminthes 4. What is an amniotic egg? 5. Name three characteristics that separate primates from other mammals.