Practice Questions for Exam Practice Questions for Exam 11

Reproduction that occurs when a Reproduction that occurs when a portion of a parent splits off to form a portion of a parent splits off to form a new individual isnew individual isa. Asexuala. Asexualb. Buddingb. Buddingc. Sexualc. Sexuald. a and bd. a and be. None of the abovee. None of the above

Which one of the following regarding Which one of the following regarding the protozoans isthe protozoans is false false??

a. They are often coloniala. They are often colonial

b. Some have chloroplasts and b. Some have chloroplasts and photosynthesizephotosynthesize

c. Some possess flagella for c. Some possess flagella for locomotionlocomotion

d. They are metazoand. They are metazoan

e. Some reproduce by fissione. Some reproduce by fission

Biology 320Biology 320Invertebrate ZoologyInvertebrate Zoology

Fall 2005Fall 2005

Chapter 9 – Introduction to Chapter 9 – Introduction to BilateriaBilateria

BilateriaBilateria Majority (99%) of eumetazoans Majority (99%) of eumetazoans

exhibit bilateral symmetryexhibit bilateral symmetry

These organisms are lumped These organisms are lumped into the taxon Bilateriainto the taxon Bilateria

Has led to the enhancement of Has led to the enhancement of neuromuscular systemsneuromuscular systems

Major milestone - cephalizationMajor milestone - cephalization

Therefore, has allowed the Therefore, has allowed the colonization of more colonization of more physiologically challenging physiologically challenging habitatshabitats

In particular, terrestrial habitatsIn particular, terrestrial habitats

Also allowed the attainment of Also allowed the attainment of larger body sizeslarger body sizes

90m in the blue whale90m in the blue whale

Bilateral SymmetryBilateral Symmetry

Animal has only one plane of Animal has only one plane of bisectionbisection Known as midsaggital planeKnown as midsaggital plane Produces left and right Produces left and right

mirror-image halvesmirror-image halves

Body polarized along two axisBody polarized along two axis Anterior / posterior (head / Anterior / posterior (head /

tail)tail) Ventral / dorsal (belly / back)Ventral / dorsal (belly / back)

Most likely evolved from Most likely evolved from organisms who began organisms who began spending time at air / water spending time at air / water interfaceinterface

Bilateral symmetry is Bilateral symmetry is most often seen in most often seen in animals that move animals that move horizontally through horizontally through habitathabitat Useful because food / Useful because food /

mates usually mates usually randomly distributedrandomly distributed

Sessile animals often Sessile animals often filter feedfilter feed Radial symmetry is Radial symmetry is

suitable to lifestylesuitable to lifestyle Plankton / particulate Plankton / particulate

matter is somewhat matter is somewhat uniformly distributed uniformly distributed

CephalizationCephalization

Means “head development”Means “head development”

Anterior localization of CNS Anterior localization of CNS and sensory structuresand sensory structures Brain usually one or more Brain usually one or more

ganglial complexesganglial complexes Vertebrates have skull and Vertebrates have skull and

spinal column to protect spinal column to protect large CNSlarge CNS

Exhibited by motile Exhibited by motile bilateriabilateria

Allows motile animals to Allows motile animals to detect and pursue food, detect and pursue food, mates, shelter, etc.mates, shelter, etc.

Mouth at anterior endMouth at anterior end

Longitudinal nerve Longitudinal nerve cordscords Usually pairedUsually paired

Often have giant axons for Often have giant axons for rapid conductance (low rapid conductance (low resistance), presumably for resistance), presumably for escape responseescape response

To contrast motile To contrast motile bilateria, sessile bilateria, sessile bilateria usually are bilateria usually are not cephalizednot cephalized May have radially symmetric May have radially symmetric

portions such as crown of portions such as crown of tentaclestentacles

MusculatuMusculaturere

As many are motile, often As many are motile, often have obliquely / cross have obliquely / cross striated muscle for rapid striated muscle for rapid contractioncontraction Remember, smooth muscle Remember, smooth muscle

contracts slowlycontracts slowly

Outer layer of circular Outer layer of circular muscle almost always muscle almost always encloses an inner encloses an inner longitudinal layerlongitudinal layer Especially true in vermiform Especially true in vermiform

animalsanimals

Contraction of circular Contraction of circular muscles produces elongationmuscles produces elongation Due to hydrostatic skeletonDue to hydrostatic skeleton

Longitudinal muscle Longitudinal muscle contractions allow for: contractions allow for: Bending Bending UndulatingUndulating Shortening / retraction Shortening / retraction

of posterior endof posterior end

PeristalsisPeristalsis Coordinated / alternating Coordinated / alternating

contractions of circular contractions of circular and longitudinal musclesand longitudinal muscles

Useful for forward Useful for forward propulsion and burrowingpropulsion and burrowing

Other types of Other types of musculaturemusculature Dorsoventral – flatteningDorsoventral – flattening Helical – twistingHelical – twisting

Bilaterian Bilaterian CompartmentalizationCompartmentalization

Important for specialization of physiological Important for specialization of physiological regulationregulation

Cnidarians first evolved a cavity for extracellular Cnidarians first evolved a cavity for extracellular digestiondigestion However, the gastrovascular cavity is not specializedHowever, the gastrovascular cavity is not specialized Carries out multiple functionsCarries out multiple functions

Example, bilaterian gut specializes in digestion Example, bilaterian gut specializes in digestion and absorptionand absorption

Bilaterians have evolved other body systems that Bilaterians have evolved other body systems that increase physiological compartmentalizationincrease physiological compartmentalization CoelomCoelom Hemal systemHemal system

The Bilaterian GutThe Bilaterian Gut

More primitive bilaterians More primitive bilaterians still posses a blind gutstill posses a blind gut

Many have a true gut (hollow Many have a true gut (hollow tube) that is composed of tube) that is composed of specialized regionsspecialized regions Mouth and foregut – Mouth and foregut –

ingestion and initial ingestion and initial digestiondigestion

Midgut – chemical digestion Midgut – chemical digestion and absorptionand absorption

Hindgut and anus – Hindgut and anus – elimination of wastes, elimination of wastes, reclamation of water, and reclamation of water, and ion regulationion regulation

Origins of gut regionsOrigins of gut regions Foregut and hindgut develop from embryonic ectodermForegut and hindgut develop from embryonic ectoderm Midgut develops from embryonic endoderm; becomes Midgut develops from embryonic endoderm; becomes

gastrodermisgastrodermis

Specialized structures of gut regionsSpecialized structures of gut regions ForegutForegut

Buccal cavity – chamber that receives food and may house Buccal cavity – chamber that receives food and may house teethteeth

Pharynx – throat that may be protrusible in some animalsPharynx – throat that may be protrusible in some animals Esophagus – ciliated portion that links foregut and midgutEsophagus – ciliated portion that links foregut and midgut

MidgutMidgut Stomach – enlarged for digestionStomach – enlarged for digestion Intestine – forms feces and joins hindgutIntestine – forms feces and joins hindgut Ceca – outpockets of stomach or intestine that increase SA for Ceca – outpockets of stomach or intestine that increase SA for

digestion, absorption, and/or storagedigestion, absorption, and/or storage

HindgutHindgut Rectum – receives indigestible wastesRectum – receives indigestible wastes Cloaca – name for rectum if gonoducts / excretory ducts empty Cloaca – name for rectum if gonoducts / excretory ducts empty

herehere

Keep in mind, names of gut regions and structures Keep in mind, names of gut regions and structures are not standardized across the phyla!are not standardized across the phyla!

CoelomsCoeloms Fluid-filled cavity lined with mesodermally derived Fluid-filled cavity lined with mesodermally derived

epithelium (mesothelium)epithelium (mesothelium) Fluid is known as coelomic fluidFluid is known as coelomic fluid Circulated by mesothelial cilia or muscular contractionsCirculated by mesothelial cilia or muscular contractions

FunctionsFunctions Houses organsHouses organs Hydrostatic skeletonHydrostatic skeleton CirculationCirculation ReproductionReproduction ExcretionExcretion

Three typesThree types Acoelomates – typical of small animals as they are not Acoelomates – typical of small animals as they are not

diffusion limiteddiffusion limited Pseudocoelomates – cavity not entirely lined with mesotheliumPseudocoelomates – cavity not entirely lined with mesothelium Coelomates – true body cavity lined with mesoderm-derived Coelomates – true body cavity lined with mesoderm-derived

mesothelium or peritoneummesothelium or peritoneum

Segmentation occurs Segmentation occurs when coelom is when coelom is partitioned by:partitioned by: Mesenteries – Mesenteries –

longitudinallongitudinal Septa – transverseSepta – transverse

Benefit is that each Benefit is that each segment can be segment can be regulated individuallyregulated individually LocomotionLocomotion Loss of some Loss of some

segments may not be segments may not be life threateninglife threatening

Hemal SystemHemal System Essentially a circulatory Essentially a circulatory

system that consists of:system that consists of: Blood (called hemolymph in Blood (called hemolymph in

most inverts)most inverts) VesselsVessels SinusesSinuses

Blood is usually circulated Blood is usually circulated via muscular contractionsvia muscular contractions

Hemal system is usually Hemal system is usually absent in small animalsabsent in small animals

Some organisms (especially Some organisms (especially pseudocoelomates) have a pseudocoelomates) have a hemocoelhemocoel Large circulatory sinus that Large circulatory sinus that

doubles as main body cavitydoubles as main body cavity

ExcretionExcretion Larger animals have Larger animals have

nephridia (little kidneys)nephridia (little kidneys)

Remove nitrogenous Remove nitrogenous waste and osmoregulatewaste and osmoregulate

Wastes are removed w/ Wastes are removed w/ water out of a water out of a nephridioporenephridiopore

Variation in nephridiaVariation in nephridia

Cleavage PatternsCleavage Patterns

Diagnostic tool for Diagnostic tool for systematicssystematics

Radial cleavageRadial cleavage Cleavage planes are parallel Cleavage planes are parallel

or perpendicular to axis of or perpendicular to axis of zygotezygote

Occurs in cnidarians, Occurs in cnidarians, lophophorates, and lophophorates, and deuterostomes (covered next) deuterostomes (covered next)

Spiral cleavageSpiral cleavage Cleavage planes are oblique Cleavage planes are oblique

to axis of zygoteto axis of zygote Occurs in flatworms, molluscs, Occurs in flatworms, molluscs,

segmented worms, etc.segmented worms, etc.

Coelom FormationCoelom Formation EnterocoelyEnterocoely

Outfoldings of Outfoldings of archenteron pinch archenteron pinch offoff

Occurs in Occurs in deuterostomesdeuterostomes

SchizocoelySchizocoely Coelom splits early Coelom splits early

in developmentin development Forms segmental Forms segmental

coelomic cavitiescoelomic cavities

Divisions of BilateriaDivisions of Bilateria

Two major divisionsTwo major divisions Protostomia – molluscs, annelids, and arthropods Protostomia – molluscs, annelids, and arthropods Deuterostomia – echinoderms and chordatesDeuterostomia – echinoderms and chordates

ProtostomesProtostomes Spiral cleavageSpiral cleavage SchizocoelySchizocoely Blastopore becomes mouthBlastopore becomes mouth

DeuterostomesDeuterostomes Radial cleavageRadial cleavage EnterocoelyEnterocoely Blastopore becomes anus, and mouth forms elsewhereBlastopore becomes anus, and mouth forms elsewhere