Vertebrate Relationships and Structure

1. Vertebrate Relationships and Structure Chapter 2

2. What is a vertebrate • Classification • Kingdom: Animalia • Phylum: Chordata • Subphyla • Vertebrata • Urochordata • Cephalochordata

3. What is a vertebrate? • Is a chordate • Chordates have shared derived and primitive characters seen in all members of the phylum • multicellular

4. Shared Derived Characters of Chordates: • Notochord • Long and dorsal, flexible rod which runs the length of the back in some kinds • In vertebrates, the notochord appears in the embryo and then later develops into part of the backbone. • Made from cartilage • The notochord serves as the skeletal structure and support of all chordates, and it is from the notochord that chordates derive their name

5. Shared Derived Characters of Chordates • Dorsal Hollow Nerve Cord • A bundle of nerve fibers which runs down the back . • The dorsal nerve cord lies directly above the notochord : supported by the notochord • Connects brain and with lateral muscles and other organs

6. Muscular Post-anal tail • Represents posterior elongation of body beyond anus. • A postanal tail (post = behind, after; anal refers to the anus) is present and extends behind the anus in many taxa, thus the anus isn’t at posterior tip of body. In humans, the tail is present during embryonic development, but is subsequently resorbed.

7. Endostyle • A groove below the pharynx or throat. • Secretes mucus for trapping food during filter feeding • Present in tunicates and cephalochordates • Homologous to the thyroid gland in vertebrates

8. Pharyngeal slits • are openings through which water is taken into the pharynx, or throat. • In primitive chordates the pharyngeal slits are used to strain water and filter out food particles; • in fishes they are modified for respiration- gills. • Most terrestrial vertebrates have pharyngeal slits only in the embryonic stage. • Seen in hemichordates: sister taxon • pharyngeal slits are only present in the human fetus

9. Shared Primitive Characters • Bilateral symmetry • Coelomate body plan • Segmentation • Deutrostome developments • Chordates are deutrostomates • In deutrostomes the anus comes from an early opening called a blastopore. Initial opening of the digestive tract is the anus • Mouth develops later

10. Sister Taxon to Chordates: next of Kin • Closest non-chordate relatives • Hemichordates and • Echinoderms • Shared Primitive Characters include • Bilateral symmetry • Coelomate body form • Segmentation • Deutrostome development • Pharyngeal slits only seen in Hemichordates

11. Sister Taxon to Chordates: next of Kin • Modern Echinoderms lack the pharyngeal slits • May have existed in extinct individuals, hence further away from the chordates compared to hemi-chordates • See figure 2.1

12. Non-vertebrate Chordates: Subphylum: Urochordate • Relative of vertebrates in phylum chordata • Represented by tunicates (or sea squits) • Sessile marine animals (invertebrates): attach to the sea-bed • Filter feed food particles: have an endostyle and pharyngeal slits for filter feeding. • Have a notochord, dorsal hollow nerve cord and post-anal tail

13. Urochordate • In general little resemblance to vertebrates • Start off as tad-pole like larva with a notochord. • Several authors have argued for the urochordata to be the sister taxon of vertebrates. Early verts. Possibly originated from a tunicate-like larva that became sexually mature without metamophorphosis to the adult body plan thru a process called paedomorphosis.

14. Non-vertebrate Chordates: Subphylum: Cephalochordate • ~ 22 speciec • Small, fishlike marine animals (,5 cm) • Lancelets are common bottom-dwelling forms that possess all four chordate characteristics (a notochord, dorsal tail, etc) • Commonly called amphioxus or Brachiostoma • No distinct head or tail; both ends sharp or pointed • Sedentary as adults; pharyngeal slits for filter feeding • See figure 2.2 (a, b)

15. Cephalochordate • Contain myomeres (muscle fiber blocks) • Body divided by myomeres • Notochord extend the whole body • Gas exchange is by diffusion • Coelom- internal body cavity • External boy cavity called atrium which opens outside thru an atriopore • Atrium lost in vertebrates: primitive trait

16. Why are sister taxon to vertebrates • Shared derived characters • Muscle segments • Circulatory system with a heartlike structure • Excretory tissue is formed from cells called podocytes: • No kidneys in amphioxus

17. Subphylum Vertebrata • Define a vertebrate • Members of Phylum chordata • Show major chordate features • A. Vertebral column/backbone • Typical feature • Surround and protects main nerve cord • Replaces original notochord after embryonic development • Fishes: vertebrae is made up of cartilage or bone.

18. Vertebral Column: Centrum • The centrum is the main bony disk-shaped or spool-shaped portion of the vertebra; it forms around, and usually replaces, the notochord. On the dorsal side of the centrum is the neural arch, through which the nerve cord or spinal cord passes. It is the main body of a vertebrae • In jawed fishes, it is the bony portion of the vertebrae that surrounds the notochord; Jawed fishes retain a notochord into adultwood • Seen in jawed fishes (Gnathostomes)

19. Cranium • Skull, surround the brain • Hagfishes (jawless vertebrate: agnatha) have remnants of cranium but no vertebrae • Lampreys (jawless vert, agnatha) have a rudimentary cartilaginous vertebrae • Craniata • Name proposed to replace vertebrata since Hagfishes have no vertebrae but are in the subphylum • However, loss of vertebral elements maybe derived, hence hagfishes included with hagfishes.

20. Hox gene complex duplication • Belong to the homeobox gene family.  • The homeobox gene family encodes a cluster of genes that encode a specific body part. Thus regulate other genes that code for the shape of the body • Thus control regional differentiation during embryonic development

21. Neural Crest tissue • Believed to be a 4th embroyonic germ tissue (besides, endoderm, ectoderm, mesoderm) • Vertebrates are quadroblastic with 4 germ layers • N. tissue gives rise to • Head tissues • Peripheral nervous system • Adrenal glands • Pigment cells in the skin (melanocytes) • Secretory cells of the gut • Smooth muscle tissue lining the aorta

22. 3-part Brain • Forebrain, midbrain, hindbrain • Brain of cephalochordates is undivided • Telencephalon • Portion of the forebrain that bears the cerebral cortex • Area of higher processing in vertebrate

23. Summarize Definition of a vertebrate • A chordate with a cartilaginous or bony endoskeleton. Shared derived characters are • Serially arranged vertebrae • Cranium • 3-part brain • Duplication of hox gene complex • Presence of neural crest.

24. Structure of Vertebrates • See table 2.1 and figure 2.4

25. Embryology • Study of embryonic development helpful in determining phylogeny of various organisms • Need to be familiar with beginning of embryonic development.

26. Embryology: germ layers • Three are first seen during gastrulation • This is the embryonic stage when first primitive germ layers form

27. Embryology: germ layers: • ECTODERM • Forms the epidermis (skin ), lining of the anterior & posterior ends of the gut and the nervous system • ENDODERM • Innermost layer- • Lining of gut and glands of the gut • Lining of respiratory structures • Liver, pancreas

28. Embryology: germ layers • Mesoderm • Middele layer; last to appear • Forms muscle, notochord and skeleton, connective tissue, circulatory system, urogenital system • Splits to form a coelom • Coelom contains internal organs • Divided into 2 cavities

29. Embryology: germ layers Mesoderm • Pleuroperitoneal cavity (Lungs and abdomen) • Around the internal organs (Viscera) • Lined by a thin sheet of mesoderm called peritoneum • Pericardial cavity • Around the heart • Lined by pericardium

30. Embryology: germ layers • Neural Crest • 4th germ layer characteristic of vertebrates

31. Vertebrate Embryo: Figure 2.5 • Chordate features shown are: • Pharyngeal pouches and clefts • Pharyngeal grooves- will later become gills in fish but dissappear in land vertebrates • Pharyngeal tissue (lining) develops into glandular structures of the lymphatic systems • Thymus gland, parathyroid glands, carotid bodies and tonsils • Dorsal hollow nerve cord • Notochord

32. Embryonic Mesoderm: 3 regions • Dorsal mesoderm next to the nerve cord • Forms the somites (epimere). Form segmented body parts • Somites form along both sides of the notochord. • Segmented portion that forms • Dermis of skin • Striated muscles of the body for mvnt • Dorsal segmented muscles (epaxial) • Some epaxial muscles form the hypaxial muscles on the ventral side of the body • Part of the vertebral column and skull

33. Embryonic Mesoderm: 3 regions • Lateral Plate • Ventral embryonic mesoderm • Called hypomere • Forms all internal and non-segmented portions of the body • Connective tissue • Blood vessels • Mesentries • Peritoneum (peritoneal and pericardial • Reproductive system • Smooth muscles of the gut • Heart muscles, smooth muscles, girdles

34. Embryonic Mesoderm: 3 regions • Nephrotomes • Middle part of the mesoderm • Segmented • Links somites & lateral plate • Forms the kidneys (segmented) • Kidney drainage ducts (archinephric ducts) • Gonads (testes and ovaries)

35. Adult Tissue Types • 5 kinds of tissues • Epithelial • Connective • Vascular • Muscular • Nervous • Form larger organs

36. Adult Tissue Types • Collagen • Fibrous protein in all tissues • Mesodermal protein • Part of bone, tendons, ligaments • Soft, non stretching. • Elastin • Flexible protein, stretches, recoils and recoil. • Function s in connective tissue together with collagen. • Provides elasticity, collagen provides rigidity to connective tissue.

37. Adult Tissue Types • Keratin • is a highly fibrous protein that is the primary material in the cells of the skin, hair and nails, horns, feathers, claws, beaks, • the outer covering of the body

38. Basic Organ Systems: The Integument • The outer covering of the body : • Skin and it derivatives • Single organ: makes 15-20% of body • Divided into 3 parts • Epidermis • Dermis • Deep layer, support the epidermis, contains vascular tissue and nervous tissues • Hypodermis • Deepest layer, stores fat (subcutaneous) • Also striated muscles

39. Functions of the integument • Protection from pathogens • Exchange of materials with env • Sensation (input to NS) • Contain melanocytes: house pigment cells • Cells contain melanin • Prevents water loss • Secretes (mucus, poison and , sweat glands) • Stores subcutaneous fat in hypodermis

40. Skeleton system: made of Mineralized tissue • Made of collagen fibers and Hydroxyapatite • Ca and P deposits • Hardy mineral resistant to acids • Resists lactic acid

41. Types of Mineralized tissuea. enamel • 99% mineralized (entirely Ca and P) • In teeth of vertebrates (hardest) • Teeth long lived, fossil records • In dermal skeleton of some fishes • Mineralized exoskeleton • dermal bone elements are usually present in the head region • early vertebrates (ostracoderms) had so much dermal bone they were called 'armored fishes' • Ectodermal

42. b. Dentine • Inner layer of teeth • Forms the root and inner core of the tooth crwon • Contains cells called odontoblasts • 90% mineralized • In teeth and dermal armor of primitive fishes • Mesodermal( formed from neural crest)

43. C. Cartilage • Mineralized in sharks but not in other vertes • Forms internal skeleton in sharks and other cartilagenous fishes • Mesodermal • Formed by cells called chondrocytes • Calcified cartilage has no blood vessels, cannot remodel itself.

44. d. Enameloid • Resembles enamel • Seen in most fishes • It’s a primitive vertebrate condition • Formed from mesodermal cells

45. e. Cementum • Bone like substance that fastens the teeth in their sockets • Outer covering of a tooth’s root • Hard but thin • _____________________________ • Primitive teeth of veetebrates - odontodes • Vertebrate teeth have Outer layer: enamel or enameloid • Inner layer: dentine • Central part: pulp cavity • Shark scales : dermal denticles: similar structure to teeth.

46. d. BONE • Made of collagen fibers, protein secreting cells, hydroxyapatite • Bone cells (osteocytes) are called osteoblasts, form bone • 50 % mineralized • Formed by mesodermal cells • Highly vascularised, can self remodel • Osteoclasts cells that remove old bone

47. Types of Bone: Dermal Bone • Develops in the skin • First type of bone to evolve in vertebrates • Formed external armor in early fishes (ostracoderms) • Gave rise to many bones: skull, pectoral girdle • Thus vertebrates do not only possess endoskeleton

48. b. Endochondral bone • Form inside cartilage • Becomes internal skeleton in bony fishes and descendants • Formed in and replaces cartilage • Cartilage destroyed by the process of calcification. • Cartilage is then reabsorbed.

49. Body systems

50. Skeletomuscular System • Notochord: • basic endoskeleton: a dorsal stiffening rod along the lengths of the body • Cranial skeleton • Cranium surroundd and protects brain • Formed by 3 compartments