Vertebrate Relationships and
Structure
Chapter 2
What is a vertebrate
• Classification
– Kingdom:
– Phylum:
– Subphyla
Animalia
Chordata
• Vertebrata
• Urochordata
• Cephalochordata
What is a vertebrate?
• Is a chordate
• Chordates have shared derived and
primitive characters seen in all members of
the phylum
• multicellular
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
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
• 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.
• 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
• 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
Shared Primitive Characters
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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
Sister Taxon to Chordates: next
of Kin
• Closest non-chordate relatives
– Hemichordates and
– Echinoderms
• Shared Primitive Characters include
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Bilateral symmetry
Coelomate body form
Segmentation
Deutrostome development
Pharyngeal slits only seen in Hemichordates
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
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
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.
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)
Cephalochordate
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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
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
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.
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)
•
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.
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
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
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Head tissues
Peripheral nervous system
Adrenal glands
Pigment cells in the skin (melanocytes)
Secretory cells of the gut
Smooth muscle tissue lining the aorta
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
Summarize Definition of a
vertebrate
• A chordate with a cartilaginous or bony
endoskeleton. Shared derived characters are
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Serially arranged vertebrae
Cranium
3-part brain
Duplication of hox gene complex
Presence of neural crest.
Structure of Vertebrates
• See table 2.1 and figure 2.4
Embryology
• Study of embryonic development helpful in
determining phylogeny of various
organisms
• Need to be familiar with beginning of
embryonic development.
Embryology: germ layers
• Three are first seen during gastrulation
• This is the embryonic stage when first
primitive germ layers form
Embryology: germ layers:
• ECTODERM
– Forms the epidermis (skin ), lining of the anterior &
posterior ends of the gut and the nervous system
• ENDODERM
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Innermost layerLining of gut and glands of the gut
Lining of respiratory structures
Liver, pancreas
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
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
Embryology: germ layers
• Neural Crest
– 4th germ layer characteristic of vertebrates
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
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
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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
Embryonic Mesoderm: 3 regions
• Lateral Plate
– Ventral embryonic mesoderm
– Called hypomere
– Forms all internal and non-segmented portions of the
body
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Connective tissue
Blood vessels
Mesentries
Peritoneum (peritoneal and pericardial
Reproductive system
Smooth muscles of the gut
Heart muscles, smooth muscles, girdles
Embryonic Mesoderm: 3 regions
• Nephrotomes
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Middle part of the mesoderm
Segmented
Links somites & lateral plate
Forms the kidneys (segmented)
Kidney drainage ducts (archinephric ducts)
Gonads (testes and ovaries)
Adult Tissue Types
• 5 kinds of tissues
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Epithelial
Connective
Vascular
Muscular
Nervous
• Form larger organs
Adult Tissue Types
• Collagen
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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.
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
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
Functions of the integument
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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
Skeleton system: made of
Mineralized tissue
• Made of collagen fibers and
Hydroxyapatite
– Ca and P deposits
– Hardy mineral resistant to acids
– Resists lactic acid
Types of Mineralized tissue
a. 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
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)
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.
d. Enameloid
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Resembles enamel
Seen in most fishes
It’s a primitive vertebrate condition
Formed from mesodermal cells
e. Cementum
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Bone like substance that fastens the teeth in their sockets
Outer covering of a tooth’s root
Hard but thin
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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.
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
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
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.
Body systems
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
Skeletomuscular System: cranium
parts
• Chondrocranium
– Surround brain; Formed by neural crest
– Either cartilage (primitive or endochodral)
• Splanchocranium
– Made from neural crest tissue
– Either cartilage or endochondral
• Dermatocranium
– Contain dermal bone
– Cartilaginous in some fishes
Skeletomuscular System: Cranial
Muscles
• Striated muscles in the head region
– Transverse stripes on muscles
– Connected on either or both ends to a bone and
so move parts of the skeleton
• 2 types of striated muscles
– Branchiomeric
• Assoc. with splanchocranium, gills, jaws
• Function in feeds and feeding
• Innervated by dorsal nerves from brain
Skeletomuscular System: Cranial
Muscles
• Extrinsic muscles
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Eye muscles: 6 in each eye
Rotate the eye ball in all vertebrates
Not seen in hagfishes
Controlled by somatic motor nerves
AXIAL SKELETON
• Includes: vertebral column, ribs, limbs, girdles,
cranium parts
• Axial muscles
– Myomeres (segmented muscles)
– Have a V-shape in non-vertebrates (amphioxus)
– W-shaped in other vertebrates (see figure 2.10)
• Lamprey (jawless) shark (jawed)
– Segmention most visible in fishes . Muscle blocks
which are myomeres
Locomation
• Vertebrates characterized by mvnt
• Aquatic larval forms use cilia
• Larger chordates: serial contractions of
segmented muscles in truck and tail
• Segmented muscles attach to notochord
Feeding & Digestion systems
• Feeding is
– Process of taking food items into oral chamber
– Processing (if any) e.g. chewing
– Swallowing
• Digestion
– Process of breaking down food into smaller
units for absorption
Digestive System
• Non-vertebrates chordates (amphioxus)
– Filter feed
– Digest feed in gut cells
• Primitive vertebrates: Lampreys
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Filter feeding using pharyngeal slits
No stomach
No division of intestine; no rectum
Intestines open into a cloaca
• Common opening for digestive, urtinary and reproductive
systems in many vertebrates
Digestive System
• Divided into
– Esophagus, stomach, intestines, cecum, large
intestine, anus
– Herbivores have large and digestive system
– Enzymes produced by pancreas, liver, intestinal
walls, stomach lining etc.
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Respiratory System
• Allows exchange of gases between the body
and the environment.
• Occurs in various ways
– Aquatic: gills
– Aquatic (amphioxus) cutaneous (skin)
– Aquatic and terrestrial : lungs
Cardiovascular system
• Function
– Transports gases, nutrients, heat throughout the body
– Immunological response cells (WBC)
• Closed: blood enclosed in within vessels
– Arteries: carry blood away from heart
– Veins: carry blood to heart
– Capillaries are sites of exchange between blood and
tissues: form capillary beds
Cardiovascular system
• Heart
– Muscular heart
– Pumps blood
– Primitively: 3 major compartments
• Sinus venous
– Mostly seen in amniotes & reptiles
– Most posterior chamber
– Receives blood from systemic veins
Cardiovascular system: heart
• Atrium
– With valves to prevent backflow
• Ventricle
– Primary pumping chamber
• Study the basic plan of the circulatory
system (fig 2.11 a) for general (primitive)
scheme of blood flow
Cardiovascular system: Blood
Flow
• Heart  ventral aortagills (for oxygen)
• Gills dorsal aorta(has O2)
• Dorsal aorta divides into Carotid arteries that
supply the head and mesenteric arteries that
supply the gut
• From tissues blood returns to heart via cardinal
veins
– Anterior cardinal veins(Jugular):from head
– Posterior cardinal vein: from body
Cardiovascular
system:terminology
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Plasma: liquid part of blood
Hemoglobin: iron rich proteins that carry oxygen
Erythrocytes: RBC
Leukocytes: WBC
Thrombocytes: Clotting cells: Platelets
Arteriovenous anastomosis: direct connection
between arterioles and venules that bypass the
capillary system. Blood by passes the capillaries
Cardiovascular
system:terminology
• Presphincter muscles: muscles that regulate blood
flow through the capilllaries
• Portal veins: Blood vessels that begin and end in a
capillary bed. Transport substances from site of
production to site of action
• Hepatic Portal veins:
– Veins between GIT and lungs
• Renal portal vein: between body and kidneys
Excretory system
• Kidney is the primary organ
• 2 primary functions
– Dispose nitrogen wastes: by products of pn metabolism
– Regulate salt, water balance (osmoregulation)
• Development
– From the nephrotome (mesomere)
– Embryonic tissue between the epimere and hypomere
Excretory system: Kidney
structure
• 3 regions seen at embryonic stage
– 1.
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Pronephros
Anterior most segment
Tubules called pronephric tubules
They form the archinephric duct
Develops early in all vertebrate embryos
Regresses in most vertebrates
Functional in embryos and hagfishes and
Excretory system: Kidney
structure
• 2. Opisthonephros
– Replaces the pronephros
– Formed by 2 regions mesonephros (middle) and
metanephros (posterior)
– Seen in fishes and amphioxus
– Kidney of fishes tend to be long and segmented
Excretory system: Kidney
structure
• 3. Metanephric Kidney
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Includes only the metanephros
Drained by ureters
Bean shaped
Kidney of amniotes (synapomorphy)
Reproductive system
• Gonads: unsegmented, paired, posterior to
body wall, lie behind the peritoneum
– Ovaries:
• contains follicles (primary cells) – produce ovum
• Produce estrogens,
• Ovulation (Oviducts-Passageway for eggs)
– Testes
• Seminiferous tubules (functional)
• Produce testosterone
Reproductive system: Sertoli
cells
• Sertoli cells are the somatic cells of the testis that are
essential for testis formation and spermatogenesis.
Sertoli cells facilitate the progression of germ cells to
spermatozoa via direct contact and by controlling the
environment milieu within the seminiferous tubules.
• The regulation of spermatogenesis by FSH and
testosterone occurs by the action of these hormones on
the Sertoli cells.
• While the action of testosterone is necessary for
spermatogenesis, the action of FSH minimally serves to
promote spermatogenic output by increasing the
number of Sertoli cells.
Coordination and Integration:
Nervous system
• Neuron= basic structural unit
– Have axons, dendrites,cell bodies (have nucleus)
– Axons encased in myelin sheaths
– Collection of axons =
• Nerves in PNS
• Tracts in CNS
• Nerve cord= spinal code
– Gray matter: cell bodies
– White matter: myelin covered axons
– Connects brain with body, controls swimming in fish, hand reflexs
before impulse reach the brain.
Nervous system:Peripheral
Nervous System
• Nerves exit from spinal cord between
vertebrae
• Divided into two
– Somatic nervous system
– Visceral nervous system
Peripheral Nervous System:
Somatic nervous system
• Voluntary system
– Innervates the striated muscles of the limb
– Responds to pain and temperature receptors
• Somatic motor fibers carry impulses from CNS to
body muscles
• Somatic sensory fibers relay information to the CNS
from muscles
Peripheral Nervous System:
Visceral nervous system
• Consists of sensory neurons and motor neurons that run
between the central nervous system (especially the
hypothalamus and medulla oblongata) and various
internal organs such as the:
– heart , lungs,viscera,glands
• The actions of the system are largely involuntary
• Forms the autonomic nervous system
• Divided into two
– Sympathetic nervous system
– Parasympathetic nervous system
Sympathetic Nervous System
• sympathetic branch of the autonomic nervous system
prepares the body for emergencies: for "fight or flight".
• Stimulates heart beat
• Raises blood pressure
• dilates the pupils
• dilates the trachea and bronchi
• stimulates the conversion of liver glycogen into glucose
• shunts blood away from the skin and viscera to the skeletal
muscles, brain, and heart
• inhibits peristalsis in the gastrointestinal (GI) tract
• inhibits contraction of the bladder and rectum
Parasympathetic Nervous System
• Parasympathetic stimulation causes
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slowing down of the heartbeat
lowering of blood pressure
constriction of the pupils
increased blood flow to the skin and viscera
peristalsis of the GI tract
• In short, the parasympathetic system returns the body
functions to normal after they have been altered by
sympathetic stimulation.
• In times of danger, the sympathetic system prepares the
body for violent activity. The parasympathetic system
reverses these changes when the danger is over.
Cranial Nerves
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Nerves of the somatic nervous system
Emerge from the brain
10 pairs in primitive vertebrates
12 pairs in amniotes
Numbered by roman numerals
Vagus nerve (Cranial nerve 10)
– Main nerve of parasympathetic nervous system
– Has mixed sensory and motor neurons
Brain Anatomy
• Forebrain
– Has two parts
– Diencephalon: posterior region associated with
• Pituitary gland: endocrine gland: outgrowth from the
diencephalon
• Hypothalamus (the floor of diencephalon)
• Pineal gland: dorsal outgrowth of the diencephalon
– Telencephalon
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Is the cerebrum (cerebral hemisheres)
Associated with learning and language devt in humans
Very large in tetrapods
Tetrapods develop a neocortex: center for nervous control and
sensory integration
• The of the brain, and is the most
Brain Anatomy: Midbrain
• Associated with vision
• Receives input from optic nerves
• In mammals forebrain has taken over
functions of the midbrain
Brain Anatomy: Hindbrain
• Two parts
• Myelencephalon (medulla oblongata):
– most posterior section of hindbrain
– Controls respiration, balance and hearing
• Metencephalon
– Anterior portion
– Develops the cerebellum
• Coordinates motor activities
• Maintenance of posture
Sense Organs
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The major sensory modalities are
mechanoreception (touch and body position)
chemoreception (taste and smell)
vision (detection of light)
electroreception (detection of electrical/magnetic
fields) : mostly seen in fishes
o electric discharges from fish for communication and for
sensing predators. Receptors detect electrical currents
o acousticolateralis (hearing and motion)
Sense Organs
• Sense of vision
– Retina light receptor center
– Two photoreceptor cells
• Rods: function effectively under conditions of dim
light
• Cones: differentially sensitive to light of varying
wavelengths. Perceive color
Sense Organs: hearing
• Sense of hearing
– Inner ear for detection of sound waves in
tetrapods and some fishes
– Hair cell: basic sensory cell in inner ear- detects
fluid movement
– Neuromast organs
• Clusters of hair cells and associated structures on the
surface of the head and body of aquatic vertebrates.
• Detect movement of water across the body
Sense Organs: hearing
• Vestibular apparatus (membranous labyrinth)
– Part of the inner ear that contain organs of balance and
cochlea (organ of hearing in tetrapods)
– Found in the optic capsule of the skull and contains
tubules and sacs with fluid called endolymph
– Contains the vestibular cells that are similar to hair cells
• Semicircular canals
– Jawed vertebrates have three canals.. They are
structures of the inner ear containing fluid that moves
through them when the head moves, signaling
rotational or angular movement to the brain
– inform the brain about tilts of the head and body.
Endocrine system
The regulation and control of various
functions are performed through
chemicals. The chemical messengers are
hormones and they are released by
endocrine glands.
Made up of small organs or scattered cells
in fishes but larger well defined organs in
amniotes.