Biology 320Biology 320Invertebrate ZoologyInvertebrate ZoologyFall 2005Fall 2005

Chapter 13 – Phylum Annelida Chapter 13 – Phylum Annelida

Part TwoPart Two

Taxon ClitellataTaxon Clitellata

Two classesTwo classes Class OligochaetaClass Oligochaeta Class HirudinomorphaClass Hirudinomorpha

Posses a clitellumPosses a clitellum Several (6 or 7 in Several (6 or 7 in LumbricusLumbricus) anterior ) anterior

segments with a thick, glandular segments with a thick, glandular epidermisepidermis

Conspicuous during reproductionConspicuous during reproduction Close proximity to gonoporesClose proximity to gonopores Produces mucus for copulation, albumen Produces mucus for copulation, albumen

for eggs, and cocoonsfor eggs, and cocoons

Lack parapodia, prostomial and pygidial Lack parapodia, prostomial and pygidial appendagesappendages

Copulating hermaphrodites with direct Copulating hermaphrodites with direct developmentdevelopment

Class OligochaetaClass Oligochaeta

Name means “few chaetae”Name means “few chaetae”

3500 spp.3500 spp.

Earthworms are most familiar, Earthworms are most familiar, but also small FW and marine but also small FW and marine varietiesvarieties 200 marine spp., mostly 200 marine spp., mostly

interstitialinterstitial

Giant Australian earthworm Giant Australian earthworm ((Megascolides australisMegascolides australis)) Up to 3 m longUp to 3 m long

Body FormBody Form Only exceptions to generalized Only exceptions to generalized

annelid are listedannelid are listed

Four bundles of chaetae per Four bundles of chaetae per segment segment Two ventralTwo ventral Two lateralTwo lateral

Chaetae are structurally simpleChaetae are structurally simple Genital chaetae are more complexGenital chaetae are more complex One to 25 chaetae per bundleOne to 25 chaetae per bundle Two per bundle in most earthwormsTwo per bundle in most earthworms Protractor and retractor muscles Protractor and retractor muscles

attached to each chaetaattached to each chaeta Small in terrestrial varieties and Small in terrestrial varieties and

longer in aquaticslonger in aquatics

CoelomCoelom

Earthworms posses coelomoporesEarthworms posses coelomopores Connect coelomic cavities with exteriorConnect coelomic cavities with exterior

Posses a sphincterPosses a sphincter

Pores are located in intersegmental furrowsPores are located in intersegmental furrows

Exude coelomic fluid dorsallyExude coelomic fluid dorsally Keeps animal moistKeeps animal moist Deters predatorsDeters predators ““Squirter worm” (Squirter worm” (DidymogasterDidymogaster) can squirt fluid 30 cm high) can squirt fluid 30 cm high

LocomotionLocomotion Crawl or burrow using peristalsisCrawl or burrow using peristalsis

Mucus and egested soil coat Mucus and egested soil coat burrow wallsburrow walls

Lumbricus terrestrisLumbricus terrestris covers covers burrow openingburrow opening

Larger worms can burrow deeperLarger worms can burrow deeper

Chaetae are extended or Chaetae are extended or retracted as needed to apply retracted as needed to apply optimal tractionoptimal traction

Animal moves forward in stepsAnimal moves forward in steps 2 – 3 cm per step2 – 3 cm per step Approximately 30 cm per minute Approximately 30 cm per minute

in somein some

Can even crawl backwardsCan even crawl backwards

NutritionNutrition

Scavengers of dead organic Scavengers of dead organic matter (such as leaves) and / or matter (such as leaves) and / or deposit feedersdeposit feeders Swallow soilSwallow soil Takes 1 – 2.5 hr to processTakes 1 – 2.5 hr to process Castings are excretedCastings are excreted Great for soil (aerates, mixes, Great for soil (aerates, mixes,

and transfers nutrients)and transfers nutrients)

Aquatic varieties may be Aquatic varieties may be carnivores of amebas, ciliates, carnivores of amebas, ciliates, rotifers, etc.rotifers, etc.

Some may parasitize FW snailsSome may parasitize FW snails

Nervous SystemNervous System One large ventral nerve cord instead of two lateral cordsOne large ventral nerve cord instead of two lateral cords

Five giant axonsFive giant axons Stimulation of either end of worm elicits an escape response Stimulation of either end of worm elicits an escape response

(wriggling, or withdrawal into burrow)(wriggling, or withdrawal into burrow)

Subpharyngeal ganglion is motor control centerSubpharyngeal ganglion is motor control center

Most lack eyes but have simple ocelliMost lack eyes but have simple ocelli

Some have rings of chemoreceptors (called tubercles) that project Some have rings of chemoreceptors (called tubercles) that project from cuticlefrom cuticle

Digestive SystemDigestive System

Pharyngeal bulbPharyngeal bulb Eversible in aquatic spp.Eversible in aquatic spp. Muscular pump in terrestrial Muscular pump in terrestrial

spp.spp. Esophageal glands secrete Esophageal glands secrete

mucus and enzymesmucus and enzymes

Compartmentalized Compartmentalized esophagusesophagus Crop for food storageCrop for food storage Gizzard for grindingGizzard for grinding

Lined with chitin-like cuticleLined with chitin-like cuticle

Calciferous GlandsCalciferous Glands

Located in wall of esophagusLocated in wall of esophagus

Produce calcite crystals that are secreted into Produce calcite crystals that are secreted into esophageal lumen and pass in fecesesophageal lumen and pass in feces

Two functional hypothesisTwo functional hypothesis 1) Removal of excess CO1) Removal of excess CO22

Soil COSoil CO22 is high (relative to atmospheric levels), due to bacterial is high (relative to atmospheric levels), due to bacterial respirationrespiration

Therefore there is a negative concentration gradient for diffusion of Therefore there is a negative concentration gradient for diffusion of worm’s COworm’s CO22

COCO2 2 combines with calcium ions to form calcite combines with calcium ions to form calcite 2) Removal of excess calcium2) Removal of excess calcium

Digestive System Cont…Digestive System Cont… Intestine makes up posterior 3/4 of Intestine makes up posterior 3/4 of

digestive systemdigestive system Anterior half secretes digestive Anterior half secretes digestive

enzymesenzymes Cellulase and chitinase (breaks down Cellulase and chitinase (breaks down

fungal cell walls) are released by fungal cell walls) are released by mutualistic bacteriamutualistic bacteria

Posterior half is absorptivePosterior half is absorptive

Typhlosole is a large dorsal fold in the Typhlosole is a large dorsal fold in the intestine that increases its surface areaintestine that increases its surface area

Chlorogogen cells surround intestineChlorogogen cells surround intestine Waste - laden cells are released into Waste - laden cells are released into

coelomcoelom Exit body via nephridiopores or Exit body via nephridiopores or

coelomoporescoelomopores

Circulation and Gas ExchangeCirculation and Gas Exchange

Often have hearts (described Often have hearts (described earlier)earlier) Five pairs in Five pairs in LumbricusLumbricus

(segments 7-11)(segments 7-11)

Gas exchange is carried out Gas exchange is carried out across body wallacross body wall Large species have capillary Large species have capillary

loops in epidermis and loops in epidermis and hemoglobin dissolved in plasmahemoglobin dissolved in plasma

Moist surface facilitates diffusionMoist surface facilitates diffusion

Oxygen levels in soil drop after Oxygen levels in soil drop after heavy rains, forcing earthworms heavy rains, forcing earthworms to the surfaceto the surface

ExcretionExcretion

Ureotelic but excrete some ammoniaUreotelic but excrete some ammonia Depends on environmental conditionsDepends on environmental conditions

OsmoregulationOsmoregulation Urine is hyposmoticUrine is hyposmotic Often several types of nephridiaOften several types of nephridia

Allows them to tolerate dry soilsAllows them to tolerate dry soils Those without special nephridia must burrow Those without special nephridia must burrow

deeper during dry periodsdeeper during dry periods

EncystmentEncystment

Can secrete tough mucus covering Can secrete tough mucus covering Summer cysts to avoid desiccationSummer cysts to avoid desiccation Winter cysts during periods of low temperatureWinter cysts during periods of low temperature

Undergo diapauseUndergo diapause

Some migrate deeper into soil during dry or Some migrate deeper into soil during dry or cold periodscold periods Up to three meters down in someUp to three meters down in some 70% of body water can be lost70% of body water can be lost

ReproductionReproduction Clonal reproduction always occurs via transverse fissionClonal reproduction always occurs via transverse fission

SexualSexual Monoecious (hermaphroditic)Monoecious (hermaphroditic)

Reproductive organs located in a few anterior segmentsReproductive organs located in a few anterior segments

Paired ovaries release eggs which develop in ovisacsPaired ovaries release eggs which develop in ovisacs

Paired testes release sperm which develop in seminal vesiclesPaired testes release sperm which develop in seminal vesicles

Genital segments each posses a pair of gonoducts (sperm ducts Genital segments each posses a pair of gonoducts (sperm ducts or oviducts), which open to the ventral surfaceor oviducts), which open to the ventral surface

Female genital segments have ventral openings that lead to Female genital segments have ventral openings that lead to seminal receptacles (store sperm prior to fertilization)seminal receptacles (store sperm prior to fertilization)

LumbricusLumbricus breeds continually, but breeds continually, but some have one yearly reproductive some have one yearly reproductive seasonseason Often reabsorb reproductive system Often reabsorb reproductive system

and grow back later and grow back later

Copulation with mutual sperm Copulation with mutual sperm transfertransfer

Ventral contact between oppositely Ventral contact between oppositely oriented wormsoriented worms Genital chaetae and mucus produced by Genital chaetae and mucus produced by

clitellum hold worms togetherclitellum hold worms together

Sperm swim in a ventral sperm Sperm swim in a ventral sperm groove from male gonopores to groove from male gonopores to openings of partner’s seminal openings of partner’s seminal receptaclesreceptacles Indirect sperm transferIndirect sperm transfer Entire process can take 2 – 3 hoursEntire process can take 2 – 3 hours

Some worms have copulatory organ Some worms have copulatory organ for direct sperm transferfor direct sperm transfer

CocoonsCocoons Secreted a few days after Secreted a few days after

copulationcopulation Clitellum secretes mucus tubeClitellum secretes mucus tube

Clitellum secretes chitinous Clitellum secretes chitinous material which becomes wall of material which becomes wall of cocooncocoon

Albumen from clitellum deposited Albumen from clitellum deposited into cocooninto cocoon

Tube slides forward as worm Tube slides forward as worm moves backwardsmoves backwards

Eggs and partner’s sperm (from Eggs and partner’s sperm (from seminal receptacles) deposited seminal receptacles) deposited into cocooninto cocoon

External fertilizationExternal fertilization Cross fertilizationCross fertilization

Cocoon slides of head, and ends Cocoon slides of head, and ends pinch off; mucus tube pinch off; mucus tube disintegratesdisintegrates

Terrestrial species deposit Terrestrial species deposit cocoons in soilcocoons in soil

Aquatic species deposit Aquatic species deposit cocoons in debris or mud, or cocoons in debris or mud, or attach to vegetationattach to vegetation

Ovoid and yellow in colorOvoid and yellow in color

Contain 1 to 20 eggsContain 1 to 20 eggs

7.5 cm X 2 cm in 7.5 cm X 2 cm in MegascolidesMegascolides

DevelopmentDevelopment

Direct developmentDirect development Therefore create eggs containing yolk or albumenTherefore create eggs containing yolk or albumen

Eight days to several months before juveniles Eight days to several months before juveniles emerge from cocoonsemerge from cocoons

Live several yearsLive several years Six years in captivitySix years in captivity

Reach sexual maturity at approximately 200 Reach sexual maturity at approximately 200 daysdays

Class HirudinomorphaClass Hirudinomorpha

Leeches and closely related wormsLeeches and closely related worms

500 spp500 spp Marine, mostly freshwater, a few Marine, mostly freshwater, a few

terrestrial species (restricted to moist terrestrial species (restricted to moist environments)environments)

Lack chaetaeLack chaetae

Have a fixed number of segments Have a fixed number of segments (typically 33)(typically 33)

All have a posterior sucker for adhering All have a posterior sucker for adhering to prey or substratumto prey or substratum Most have an anterior sucker as wellMost have an anterior sucker as well

Blood-sucking ectoparasites or Blood-sucking ectoparasites or carnivorescarnivores

1 cm to 30 cm long 1 cm to 30 cm long ((HaementeriaHaementeria, giant Amazonian , giant Amazonian leech)leech)

Black, brown, olive, or red in Black, brown, olive, or red in colorcolor May have striped / spotted May have striped / spotted

patternspatterns

Typically inhabit stagnant or Typically inhabit stagnant or slow moving freshwaterslow moving freshwater Estivate in mud during periods Estivate in mud during periods

of droughtof drought Can lose 90% of body waterCan lose 90% of body water

Often extremely abundantOften extremely abundant

Body FormBody Form Dorsoventrally flattenedDorsoventrally flattened

Tapered at anterior endTapered at anterior end

SuckersSuckers Anterior (if present) is smaller and surrounds Anterior (if present) is smaller and surrounds

mouthmouth Posterior is disc-shaped; anus located directly Posterior is disc-shaped; anus located directly

anterior anterior

Annulations that don’t accurately depict Annulations that don’t accurately depict segmentssegments Number of annulations per segment variesNumber of annulations per segment varies

Clitellum spans segments 9-11, but is only Clitellum spans segments 9-11, but is only conspicuous during reproductionconspicuous during reproduction

Body WallBody Wall

Connective tissue is Connective tissue is much thickermuch thicker Makes up a larger Makes up a larger

proportion of the animalproportion of the animal

Slightly different Slightly different musculaturemusculature Dorsoventral musclesDorsoventral muscles

For flatteningFor flattening Helical musclesHelical muscles

For twistingFor twisting

CoelomCoelom Larger connective tissue Larger connective tissue compartment means a compartment means a reduction of the coelomreduction of the coelom Lack septa, so therefore lack Lack septa, so therefore lack

bilateral coelomic cavitiesbilateral coelomic cavities Also lack mesenteriesAlso lack mesenteries

Continuous coelom which Continuous coelom which serves as a hemal systemserves as a hemal system Two large lateral coelomic Two large lateral coelomic

vesselsvessels Dorsal and ventral coelomic Dorsal and ventral coelomic

vesselsvessels Lined with mesothelium Lined with mesothelium

(chlorogogen cells)(chlorogogen cells)

Muscle contractions propel fluidMuscle contractions propel fluid

Body surface conducts gas Body surface conducts gas exchangeexchange

LocomotionLocomotion Not equipped for burrowing due to:Not equipped for burrowing due to:

Reduction of coelomReduction of coelom Loss of septa and chaetaeLoss of septa and chaetae

Many inchworm by anchoring with anterior and posterior suckersMany inchworm by anchoring with anterior and posterior suckers

Many swimMany swim First contract dorsoventral muscles to increase surface areaFirst contract dorsoventral muscles to increase surface area Then undulateThen undulate

Nervous SystemNervous System

Similar to other annelidsSimilar to other annelids

Fusions of ganglia in the sucker regionsFusions of ganglia in the sucker regions

Posses ocelliPosses ocelli

Posses sensory papillaePosses sensory papillae Projecting discs consisting of many sensory cellsProjecting discs consisting of many sensory cells Typically found dorsally, in rows, on one annulation of a particular Typically found dorsally, in rows, on one annulation of a particular

segment segment

Sense organs mainly used for prey detection, and respond to:Sense organs mainly used for prey detection, and respond to: Moving shadows and water-pressure vibrations in fish leechesMoving shadows and water-pressure vibrations in fish leeches Chemicals from body fluids such as oils, sweat, and bloodChemicals from body fluids such as oils, sweat, and blood WavesWaves Temperature differencesTemperature differences

Excretory SystemExcretory System

10 – 17 pairs of metanephridia10 – 17 pairs of metanephridia One pair per segment in middle 1/3 of animalOne pair per segment in middle 1/3 of animal

Nephrostomes project into coelomic vesselsNephrostomes project into coelomic vessels

Nephridial tubules are embedded in connective Nephridial tubules are embedded in connective tissuetissue Posses a bladder that fills before urine is released Posses a bladder that fills before urine is released

through nephridioporethrough nephridiopore

Important for osmoregulationImportant for osmoregulation

Digestive SystemDigestive System Pharynx typesPharynx types

Protrusible pharynx that is forced Protrusible pharynx that is forced into prey / host tissueinto prey / host tissue

Non-protrusible sucking pharynxNon-protrusible sucking pharynx

May or may not have jawsMay or may not have jaws Enzymes usually facilitate Enzymes usually facilitate

penetration in those lacking jawspenetration in those lacking jaws

Salivary glands empty secretions Salivary glands empty secretions into pharynxinto pharynx Hirudin – anticoagulantHirudin – anticoagulant AnestheticAnesthetic VasodilatorsVasodilators

Often 1 – 11 pairs of lateral Often 1 – 11 pairs of lateral intestinal cecaintestinal ceca

NutritionNutrition

Three fourths are Three fourths are blood suckersblood suckers Usually not host Usually not host

specificspecific Usually parasitize a Usually parasitize a

group of organisms group of organisms (i.e. crayfish, fish, (i.e. crayfish, fish, reptiles, birds, reptiles, birds, mammals, etc.)mammals, etc.)

Some are carnivores Some are carnivores of small invertebratesof small invertebrates

Water from plasma is Water from plasma is excreted via nephridioporesexcreted via nephridiopores

Digestion is very slowDigestion is very slow Gut produces hardly any Gut produces hardly any

enzymesenzymes Symbiotic bacteria may Symbiotic bacteria may

produce digestive enzymes produce digestive enzymes and vitaminsand vitamins

May take 200 days to digest a May take 200 days to digest a blood mealblood meal

Rarely feedRarely feed One blood meal may increase One blood meal may increase

animals weight by 10Xanimals weight by 10X May only need to feed twice a May only need to feed twice a

year in order to growyear in order to grow Some can fast for 1.5 yearsSome can fast for 1.5 years

Medical ApplicationsMedical Applications Historically used in Europe for Historically used in Europe for

bloodlettingbloodletting

Supposedly, George Washington Supposedly, George Washington died two days after a bloodletting died two days after a bloodletting for a soar throatfor a soar throat

Hirudo medicinalisHirudo medicinalis is still used is still used today for restoring circulation and today for restoring circulation and reducing swelling after:reducing swelling after: Skin graftsSkin grafts Digit / appendage reattachmentDigit / appendage reattachment

Natural antibiotic propertiesNatural antibiotic properties Symbiotic bacteria produce Symbiotic bacteria produce

antibiotics to reduce competition antibiotics to reduce competition with other bacteriawith other bacteria

ReproductionReproduction

No sexual reproduction, including regenerationNo sexual reproduction, including regeneration

Hermaphroditic, but not simultaneousHermaphroditic, but not simultaneous

ProtandricProtandric Male portion of reproductive system develops firstMale portion of reproductive system develops first Spend first part of existence as males, then later reproduce as Spend first part of existence as males, then later reproduce as

femalesfemales

Copulation and fertilization is always internalCopulation and fertilization is always internal Most have copulatory organ for direct sperm transferMost have copulatory organ for direct sperm transfer Others hypodermically impregnate using a spermatophoreOthers hypodermically impregnate using a spermatophore

Pressure and cytolytic chemicals rupture body wall of matePressure and cytolytic chemicals rupture body wall of mate Sperm are released and migrate toward eggsSperm are released and migrate toward eggs

Eggs are laid after copulationEggs are laid after copulation Time variesTime varies

Clitellum secretes a cocoon and albumenClitellum secretes a cocoon and albumen

The cocoons of fish leeches are attached to The cocoons of fish leeches are attached to fish hostsfish hosts

Some brood eggs by attaching cocoon to Some brood eggs by attaching cocoon to substratum and ventilate eggs by fanning substratum and ventilate eggs by fanning flattened ventral surfaceflattened ventral surface

Some attach cocoon to ventral surfaceSome attach cocoon to ventral surface