Introduction to EumetazoaIntroduction to Eumetazoa

The ‘true animals’

True epithelium, definite body axes, specialized tissues

Chapter 6

EUMETAZOA

True EpitheliaTrue Epithelia

Chapter 6

EPITHELIUM – cell layer that covers surfaces, lines internal cavities and spaces

With basal lamina, apical-basal polarity, cell-cell junctions, immobile

Allows for establishment of regulated compartments (connective tissue, gut lumen, coelom)

Epithelial cells control passage of materials Environment under the epithelium can be chemically

controlled

True EpitheliaTrue Epithelia

Chapter 6

APICAL-BASAL POLARITY

BASAL LAMINA

HEMIDESMOSOMES

Epithelial Junctions•AHDERING•SEALING

• GAP

Epidermis, Gastrodermis & GutEpidermis, Gastrodermis & Gut

Chapter 6

EPIDERMIS – the outer skin; covers the surface of the eumetazoan body

Secretory Absorptive

Impermeable

GASTRODERMIS – stomach skin; epithelial layer that lines the gut and joins the epidermis at the mouth

GUT – internal, epithelia-lined cavity; it is a regulated compartment

GUT LUMEN (CAVITY) – also regulated compartment

Allows EXTRACELLULAR DIGESTION Secretes digestive enzymes and absorbs products

Connective TissueConnective Tissue

Chapter 6

CONNECTIVE-TISSUE COMPARTMENT – lies between the epi- and gastrodermis

May just be the basal lamina of the two epithelia May be very thick

CONNECTIVE TISSUE – consists of ECM and cells; no collective term for cells of the ECM

Sponges – mesohyl Metazoans – blastocoel Cnidarians – mesoglea

Bilateria – simply called ‘connective tissue’

Eumetazoan SkeletonsEumetazoan Skeletons

Chapter 6

Skeletons can:

Maintain body shape Support or protect the body

Transmit force of muscle contraction

Be internal or external Be mineral, organic or both

Be fluid or solid

Fluid SkeletonFluid Skeleton

Chapter 6

HYDROSTATIC SKELETON – water-filled skeleton, a.k.a. a hydrstat; cavity filled with water-based fluid

**This is a eumetazoan innovation!!**

Surrounded by muscles (circular and longitudinal) Muscles contract and pressurize the fluid

Water is incompressibleCIRCULAR CONTRACTION – lengthens hydrostat

and stretches longitudinal muscles LONGITUDINAL CONTRACTION – shortens hydrostat and stretches circular muscles

Utility inflate body, extend parts, locomotion, burrowing

Fluid SkeletonFluid Skeleton

Chapter 6

Orthogonal Crossed-helical

Body wall strengthened by

inelastic fibers (like collagen)

Resists aneurisms

Solid SkeletonSolid Skeleton

Chapter 6

PLIANT SKELETON – made of materials that are rubbery and elastic

RIGID SKELETON – made of materials that resist a change of shape (bone/shell)

Deform when stretched, spring back to original shape

Proteins, polysaccharides, water Use as CT in comb jellies, mesoglea in jellyfish,

hinges of bivalves

Insect framework, terrestrial and flying invertebrates, and fast moving crustaceans of the ocean

Movement and Body SizeMovement and Body Size

Chapter 6

Cilia/FlagellaCilia/Flagella MusclesMusclesVS

Only in water Associated with surface

area (effective when S/V is large)

Small, lilliputian invertebrates

Prone to surface friction and viscous drag from

environement Momentum stops when

ciliary/flagellar beat stops

Water, air, land Associated with volume Locomotion, can move

body parts with respect to other body parts (ALL

ANIMALS DO THIS) Effective when S/V is

small

MusculatureMusculature

Chapter 6

EPITHELIOMUSCULAR CELLS:Arose from epithelium.

Actin-myosin microfilaments allowed some to become

contractile.

MYOEPITHELIAL CELLS: Contractile fibers isolated in

independent cells but are still part of the epithelium.

Outside the basal lamina

MYOCYTES:True muscle, contractile cells

below basal lamina.No longer epithelial.

MusculatureMusculature

Chapter 6

SMOOTH MUSCLE: Contracts slowly.

Tension over large range of stretch lengths.

Contractile tentacles.

CROSS-STRIATED MUSCLE: Contracts rapidly.

Tension over limited range.Snapping jaws or claws.

OBLIQUELY-STRIATED: Intermediate of the other two.Extensible animals that can

make quick movements.ANTAGONISTIC

Neurons and Nervous SystemNeurons and Nervous System

Chapter 6

Eumetazoans use nerve cells to detect, evaluate, and respond to

environmental stimuli.

NEURONS - respond to stimuli by transmitting information as a

wave of depolarization to the target cells

Sensory receptors and neurons arose from epithelia (like

muscle cells).They became specialized and

migrated to a connective-tissue compartment

Neurons and Nervous SystemNeurons and Nervous System

Chapter 6

Transmission of a nerve impulse from neuron to neuron or from neuron to effector (muscle) occurs via:

Electrical junctions – gap junctions that join cells so that membrane depolarization (action

potential) spreads uninterrupted; no organismal control

SYNAPSE – gap between two cells (synaptic cleft) through which the action potential is

carried by chemical neurotransmitters

Sense Cells & OrgansSense Cells & Organs

Chapter 6

Eumetazoans need to obtain a dynamic picture of their environment so they can respond appropriately.

Response to different stimuli like:

Direction and distance to the source of the stimuli are so important to each eumtezoan

ElectromagneticElectromagnetic MechanicalMechanical

ChemicalChemical MagnMagn eticetic

Simple: sensory neuron-effector

Complex: multiple stimuli, whole-body response, accessory structures, CNS

Gravity ReceptorsGravity Receptors

Chapter 6

STATOCYSTS – hollow capsules lined with MECHANORECEPTORS and with a dense, heavy STATOLITH at the center.

Gravity pulls the statolith against the bed of mechanoreceptors

which then causes alterations of the depolarization pattern.

PhotoreceptorsPhotoreceptors

Chapter 6

CILIARY and RHABDOMERIC – can be dispersed as individual cells or, can be grouped together as EYES.

OCELLUS:PIGMENT SPOTPIGMENT CUP – EVERTED or INVERTED

DevelopmentDevelopment

Chapter 6

Zygote Cleavage Blastula *Gastrulation* Larva

Gastrulation types:INVAGINATION

EPIBOLYINGRESSION

DevelopmentDevelopment

Chapter 6

DIPLOBLASTIC – adults have 2

epithelial layers (epidermis &

gastrodermis)

TRIPLOBLASTIC – adults have 3 epithelial layers (addition of

mesothelium)

MESODERM – located between ecto- and endoderm and can arise

from either

GrowthGrowth

Chapter 6

SolitarySolitary ModularModularVS Juvenile grows via

general increase in size ALLOMETRIC – different

body parts grow at different rates

Surface > Volume Gills, lungs, gastrodermis

Associated with locomotion and increasing

complexity on one body axis

Self repair, often killed

Add new, small, identical units (module –

ZOOID) Clonal budding

All zooids form a colony Favorable SA:V

ISOMETRIC – similar growth

Colony is considered one individual

Self repair, higher survival if preyed upon

GrowthGrowth

Chapter 6

GrowthGrowth

Chapter 6

POLYMORPHISM – modular growth that results in specialization of zooids with different forms and

functions (very common in Cnidarians)

Exemplifies the replication-

specialization-integration pattern

of metazoans