Biology 320Biology 320Invertebrate ZoologyInvertebrate Zoology

Fall 2005Fall 2005

Chapter 13 – Phylum AnnelidaChapter 13 – Phylum Annelida

Part OnePart One

Phylum AnnelidaPhylum Annelida Name means “ringed”Name means “ringed”

Mostly marine, but also Mostly marine, but also freshwater and terrestrial freshwater and terrestrial representativesrepresentatives

Size varies greatlySize varies greatly Microscopic – 3 m (giant Microscopic – 3 m (giant

Australian earthworm)Australian earthworm)

12,000 spp.12,000 spp.

SegmentedSegmented

Diverse modes of feedingDiverse modes of feeding

Body RegionsBody Regions Three main regions (anterior to Three main regions (anterior to

posterior)posterior) ProstomiumProstomium

Head with sensory organsHead with sensory organs Peristomium with mouthPeristomium with mouth

TrunkTrunk Majority of body segmentsMajority of body segments

PygidiumPygidium AnusAnus Some sensory appendagesSome sensory appendages

Have annulations (superficial Have annulations (superficial segments), but also true segments), but also true segmentssegments

Internal compartmentalizationInternal compartmentalization

Growth zone is located just Growth zone is located just anterior to pygidiumanterior to pygidium

Segments added posteriorlySegments added posteriorly Oldest segment is most Oldest segment is most

anterioranterior

Some organs / structures Some organs / structures are found in every segmentare found in every segment AppendagesAppendages Coelomic cavitiesCoelomic cavities NephridiaNephridia GonadsGonads

Other organs are parts of Other organs are parts of integrated systemsintegrated systems Digestive systemDigestive system Nervous systemNervous system Hemal systemHemal system MusculatureMusculature

Segments are separated Segments are separated transversely by septatransversely by septa

Bilateral coelomic cavities Bilateral coelomic cavities are also partitioned are also partitioned longitudinally by longitudinally by mesenteries mesenteries

Generalized Body WallGeneralized Body Wall CuticleCuticle

Protective layer that resists Protective layer that resists abrasion and helps prevent abrasion and helps prevent desiccationdesiccation

Annelids are still restricted to Annelids are still restricted to moist environmentsmoist environments

EpidermisEpidermis Glandular for production of mucusGlandular for production of mucus

Previously discussed functions of Previously discussed functions of mucus apply heremucus apply here

Produce chaetaeProduce chaetae Chitinous bristles that project from Chitinous bristles that project from

epidermisepidermis Used for tractionUsed for traction Not to be confused with setae of Not to be confused with setae of

arthropods, which are sensory arthropods, which are sensory hairshairs

Connective tissueConnective tissue

MusculatureMusculature Circular and longitudinalCircular and longitudinal

Generalized Nervous Generalized Nervous SystemSystem

CNSCNS Brain is located dorsally in Brain is located dorsally in

prostomiumprostomium Two ventral longitudinal nerve Two ventral longitudinal nerve

cords with giant axonscords with giant axons Impulses travel up to 40X faster Impulses travel up to 40X faster

than neurons of average diameterthan neurons of average diameter Facilitate the escape responseFacilitate the escape response

Segmental gangliaSegmental ganglia Commissures give the nervous Commissures give the nervous

system a ladder-like appearancesystem a ladder-like appearance

Sensory structuresSensory structures Typical unicellular receptors Typical unicellular receptors

distributed on head, body, and distributed on head, body, and appendagesappendages

Polychaetes posses eyes and Polychaetes posses eyes and nuchal organs (more later) nuchal organs (more later)

Coelomic CavitiesCoelomic Cavities Two lateral coelomic cavities in each Two lateral coelomic cavities in each

segmentsegment Transverse septaTransverse septa Two longitudinal mesenteriesTwo longitudinal mesenteries

One ventral and one dorsal to gutOne ventral and one dorsal to gut

Benefit is that musculature and hydrostat of Benefit is that musculature and hydrostat of individual segments can be precisely individual segments can be precisely controlledcontrolled

Coelomic cavities may be lined with Coelomic cavities may be lined with mesothelium containing chlorogogen cellsmesothelium containing chlorogogen cells Tissue appears yellow or brown in colorTissue appears yellow or brown in color Has important metabolic functionsHas important metabolic functions

Synthesis and storage of glycogen and lipidsSynthesis and storage of glycogen and lipids DetoxificationDetoxification Hemoglobin synthesisHemoglobin synthesis Protein catabolism and formation of Protein catabolism and formation of

nitrogenous wastesnitrogenous wastes

SegmentationSegmentation

Advantages:Advantages: BurrowingBurrowing Isolation of hydrostat and Isolation of hydrostat and

muscular contractionsmuscular contractions

Studies have compared fluid Studies have compared fluid pressures in segmented pressures in segmented worms vs. non-segmented worms vs. non-segmented worms that are burrowingworms that are burrowing Pressure is transmitted Pressure is transmitted

throughout coelom in non-throughout coelom in non-segmentedsegmented

In order to prevent In order to prevent aneurisms, all muscles must aneurisms, all muscles must contract in order to contract in order to antagonize pressureantagonize pressure

Generalized Hemal SystemGeneralized Hemal System

Dorsal and ventral blood vessel, Dorsal and ventral blood vessel, which are connected by capillary which are connected by capillary bedsbeds

Blood is pumped by:Blood is pumped by: VesselsVessels Muscular contractionsMuscular contractions Enlarged portions of anterior dorsal Enlarged portions of anterior dorsal

blood vessel which function as heartsblood vessel which function as hearts

Blood may contain some hemoglobin, Blood may contain some hemoglobin, but typically larger concentrations but typically larger concentrations are contained in amoeboid are contained in amoeboid coelomocytescoelomocytes WBC + RBC hybridWBC + RBC hybrid

Gas exchange occurs across body Gas exchange occurs across body wall, appendages, and gillswall, appendages, and gills

Generalized Excretory Generalized Excretory SystemSystem

Paired segmental nephridiaPaired segmental nephridia

Funnels or terminal cells project into coelomic fluidFunnels or terminal cells project into coelomic fluid

Highly coiled tubuleHighly coiled tubule Large surface area for secretion and absorptionLarge surface area for secretion and absorption

Nephridiopore opens to exterior of animalNephridiopore opens to exterior of animal

Generalized ReproductionGeneralized Reproduction

ClonalClonal FragmentationFragmentation BuddingBudding ParatomyParatomy

SexualSexual GonochoricGonochoric External fertilizationExternal fertilization

Gametes exit through Gametes exit through nephridioporesnephridiopores

Gonads are segmental, Gonads are segmental, and housed in coelomic and housed in coelomic cavitiescavities

Trochophore larvae, with Trochophore larvae, with growth zone just anterior growth zone just anterior to the telotrochto the telotroch

Class PolychaetaClass Polychaeta

Polychaetes or bristlewormsPolychaetes or bristleworms

Name means “many chaetae”Name means “many chaetae”

8000 spp. 8000 spp.

Marine, a few freshwater, and a Marine, a few freshwater, and a few tropical terrestrial varietiesfew tropical terrestrial varieties

Diverse feeding ecology, Diverse feeding ecology, locomotion, and chaetae locomotion, and chaetae structurestructure

Also abundant (13,425 / mAlso abundant (13,425 / m22 in in Tampa Bay, FL)Tampa Bay, FL)

2 mm to 3 m (2 mm to 3 m (EuniceEunice))

Body FormBody Form Posses appendages called Posses appendages called

parapodiaparapodia Lateral outgrowths of body wall Lateral outgrowths of body wall Supported by chitinous rodSupported by chitinous rod Each segment bears one pairEach segment bears one pair Posses a chaetal sac which Posses a chaetal sac which

secretes a bundle of chaetaesecretes a bundle of chaetae

Chaetal structure is closely Chaetal structure is closely related to lifestyle and related to lifestyle and locomotionlocomotion Errant (motile)Errant (motile)

Leg shaped – crawlingLeg shaped – crawling Paddle shaped – swimmingPaddle shaped – swimming Shovel shaped – diggingShovel shaped – digging

SedentarySedentary Reduced – burrowingReduced – burrowing Hook shaped – also for Hook shaped – also for

burrowingburrowing

TubesTubes Only annelids that secrete and occupy Only annelids that secrete and occupy

tubestubes

Constructed from:Constructed from: Fibrous proteinsFibrous proteins Foreign materialsForeign materials Calcified by animal to form a shellCalcified by animal to form a shell

Tubes may be attached to a surface or Tubes may be attached to a surface or partially buried in sedimentpartially buried in sediment

Several functions:Several functions: ProtectionProtection Hide-out from which prey can be ambushedHide-out from which prey can be ambushed Brooding chamberBrooding chamber

Sometimes tubes wash up on beachesSometimes tubes wash up on beaches

Nervous SystemNervous System Typical of annelidsTypical of annelids

Segmental pedal ganglia associated with parapodiaSegmental pedal ganglia associated with parapodia

Sensory organsSensory organs Nuchal organsNuchal organs

Unique to polychaetesUnique to polychaetes Pair of eversible ciliated chemosensory pits on prostomiumPair of eversible ciliated chemosensory pits on prostomium

OcelliOcelli Best developed in errant varieties, but useful for detecting shadows in Best developed in errant varieties, but useful for detecting shadows in

sedentary wormssedentary worms StatocystsStatocysts

Useful to burrowersUseful to burrowers

Sensory appendagesSensory appendages Antennae – prostomiumAntennae – prostomium Palps – prostomiumPalps – prostomium Cirri – peristomium, parapodia, and pygidiumCirri – peristomium, parapodia, and pygidium

Digestive SystemDigestive System Typical of annelidsTypical of annelids

May have a protrusible pharynxMay have a protrusible pharynx With jaws for grasping preyWith jaws for grasping prey May be used for burrowingMay be used for burrowing

Esophageal ceca secrete digestive enzymesEsophageal ceca secrete digestive enzymes

Many strategies for waste removal, based on lifestyleMany strategies for waste removal, based on lifestyle Errant – leave wastes behind while movingErrant – leave wastes behind while moving Sedentary – interesting adaptations and behaviors to help Sedentary – interesting adaptations and behaviors to help

avoid waste contaminationavoid waste contamination Some live upside down in burrowsSome live upside down in burrows Some invert themselves just while defecating (sensory appendages Some invert themselves just while defecating (sensory appendages

on pygidium are useful here)on pygidium are useful here) May create unidirectional water flow through the burrow tubeMay create unidirectional water flow through the burrow tube

NutritionNutrition Once again, related to lifestyleOnce again, related to lifestyle

ErrantErrant Carnivores often have protrusible Carnivores often have protrusible

pharynx with jaws pharynx with jaws Herbivores or scavengersHerbivores or scavengers

BurrowersBurrowers Deposit feedersDeposit feeders

Tube dwellersTube dwellers Deposit feedersDeposit feeders

Sedentary (attached)Sedentary (attached) Suspension feed using feather crown Suspension feed using feather crown

with large SA with large SA

ParasitesParasites Endoparasites of polychaetes and Endoparasites of polychaetes and

sea starssea stars Ectoparasites that suck the blood of Ectoparasites that suck the blood of

eelseels

Gas ExchangeGas Exchange Body wallBody wall

GillsGills Exposed, delicate Exposed, delicate

outgrowths of body outgrowths of body surfacesurface

Modified portions of Modified portions of parapodiaparapodia

Feeding crowns in Feeding crowns in sedentary polychaetes, sedentary polychaetes, such as feather-duster such as feather-duster worms, double as gillsworms, double as gills

Circulatory SystemCirculatory System

Smaller varieties lack a hemal system, but Smaller varieties lack a hemal system, but possessed by larger animals possessed by larger animals

Typical annelid system plus lateral parapodial Typical annelid system plus lateral parapodial vesselsvessels

Variety of oxygen binding pigments can be found, Variety of oxygen binding pigments can be found, especially in larger animalsespecially in larger animals All function differently and have different oxygen affinitiesAll function differently and have different oxygen affinities

Intertidal polychaetes must cope with periods of Intertidal polychaetes must cope with periods of emersion or stagnation of wateremersion or stagnation of water Some undergo torpor – suppress metabolismSome undergo torpor – suppress metabolism Rely on stored oxygen from neuroglobin or myoglobinRely on stored oxygen from neuroglobin or myoglobin

ExcretionExcretion

Typically have segmental Typically have segmental nephridianephridia Occasionally localized in one or a Occasionally localized in one or a

few segmentsfew segments Feather duster worms have one Feather duster worms have one

pair of anterior nephridia that pair of anterior nephridia that empty via one medial empty via one medial nephridiopore, located on the nephridiopore, located on the headhead

Tubes are coiled to increase SA Tubes are coiled to increase SA for secretion / absorptionfor secretion / absorption

Osmoregulate in low salinity Osmoregulate in low salinity (brackish) water by increasing (brackish) water by increasing rate of filtrationrate of filtration Removes excess waterRemoves excess water A few species have even A few species have even

colonized freshwatercolonized freshwater

ReproductionReproduction

ClonalClonal All forms of clonal reproductionAll forms of clonal reproduction Excellent regeneratorsExcellent regenerators

ChaetopterusChaetopterus can grow an can grow an entire worm from one segmententire worm from one segment

SexualSexual Most only reproduce sexuallyMost only reproduce sexually Most gonochoricMost gonochoric Gonads are segmental in Gonads are segmental in

“abdomen”“abdomen” Gametes released into coelomGametes released into coelom Ripe gametes are shed via Ripe gametes are shed via

nephridiopores or rupture nephridiopores or rupture body wallbody wall

EpitokyEpitoky Reproductive phenomenon Reproductive phenomenon

characteristic of many characteristic of many polychaetespolychaetes

Worms exhibit two life phasesWorms exhibit two life phases Atoke – benthic non-reproductive Atoke – benthic non-reproductive

individual, which transforms into individual, which transforms into an…an…

Epitoke – pelagic reproductive Epitoke – pelagic reproductive individualindividual

Epitokes arise from atokes via Epitokes arise from atokes via metamorphosis or buddingmetamorphosis or budding

Undergo several modifications Undergo several modifications and essentially become and essentially become swimming sacs of gametesswimming sacs of gametes Enlargement of eyes, parapodia, Enlargement of eyes, parapodia,

and chaetaeand chaetae Become sexually mature, and Become sexually mature, and

gametes ripengametes ripen

Epitokes reach sexual Epitokes reach sexual maturity at the same time maturity at the same time and swarmand swarm

Swim to the surface and Swim to the surface and release gametesrelease gametes

Many different cues:Many different cues: Female pheromone releaseFemale pheromone release Light cyclesLight cycles Lunar cyclesLunar cycles

Very predictable patters in Very predictable patters in somesome

Some convert back into Some convert back into atokes after spawning; atokes after spawning; some reproduce once and some reproduce once and diedie

All regulated by hormonesAll regulated by hormones

OvipositionOviposition

Many shed eggs into Many shed eggs into seasea

Some attach Some attach gelatinous masses of gelatinous masses of eggs to substrataeggs to substrata Chimney of tube Chimney of tube

Some brood eggsSome brood eggs Retain eggs in tube or Retain eggs in tube or

burrowburrow Sac attached to ventral Sac attached to ventral

surface of parentsurface of parent

DevelopmentDevelopment

Trochophore larvae in mostTrochophore larvae in most Growth zone just anterior to telotrochGrowth zone just anterior to telotroch May pass through trochophore phase in egg before hatchingMay pass through trochophore phase in egg before hatching

Some direct developmentSome direct development

Life spansLife spans Some live one or two years, and reproduce once (called Some live one or two years, and reproduce once (called

annuals)annuals) Some live and breed for more than one year (perennial)Some live and breed for more than one year (perennial) Short life spans that progress through several generations in Short life spans that progress through several generations in

just one year (multiannual)just one year (multiannual)

DiversityDiversity LugwormsLugworms

Construct L-shaped burrowsConstruct L-shaped burrows Deposit feedersDeposit feeders ArenicolaArenicola

Bamboo wormsBamboo worms Construct tubes of sand that Construct tubes of sand that

resemble drinking strawsresemble drinking straws Deposit feedersDeposit feeders

Live upside down in tubes Live upside down in tubes and ingest substrate from and ingest substrate from belowbelow

ClymenellaClymenella

Paddle wormsPaddle worms Paddle-like portions of Paddle-like portions of

parapodia are used as parapodia are used as gillsgills

Errant – carnivores that Errant – carnivores that hunt prey by crawling hunt prey by crawling aroundaround

EteoneEteone tracks prey by tracks prey by following mucus trailsfollowing mucus trails

RagwormsRagworms Errant – crawl, burrow, Errant – crawl, burrow,

and swimand swim Eversible, muscular Eversible, muscular

pharynx with jawspharynx with jaws Lots of cephalic sensory Lots of cephalic sensory

structuresstructures Some reach 1.8 m Some reach 1.8 m NereisNereis

BloodwormsBloodworms Live in shallow Live in shallow

sedimentary burrowssedimentary burrows Ambush predatorsAmbush predators Capture prey with Capture prey with

extremely long extremely long eversible pharynxeversible pharynx

Have poison glandsHave poison glands GlyceraGlycera

ScalewormsScaleworms Two rows of overlapping Two rows of overlapping

scales (resemble fish scales (resemble fish scales) on dorsal scales) on dorsal surfacesurface

Scales are actually cirriScales are actually cirri AphroditeAphrodite (sea mouse) (sea mouse)

Covered with extremely Covered with extremely long chaetae that long chaetae that resembles felt or hairresembles felt or hair

FirewormsFireworms Brightly coloredBrightly colored Resemble caterpillarsResemble caterpillars Feed on corals and Feed on corals and

barnaclesbarnacles Calcified chaetae break Calcified chaetae break

off when touchedoff when touched Causes a painful, Causes a painful,

burning sensationburning sensation AmphinomeAmphinome

Shaggy tube wormsShaggy tube worms Chimneys of tubes are Chimneys of tubes are

ornamented with ornamented with foreign materials foreign materials collected by the wormcollected by the worm

Camouflage for tubeCamouflage for tube Ambush predatorsAmbush predators DiopatraDiopatra

Parchment-tube wormParchment-tube worm ChaetopterusChaetopterus Lives in U-shaped burrowLives in U-shaped burrow Filter feederFilter feeder

Seines plankton with mucus Seines plankton with mucus net it createsnet it creates

Net is rolled into a ball and Net is rolled into a ball and swallowedswallowed

Mucus is bioluminescent to Mucus is bioluminescent to ward of potential predatorsward of potential predators

Spaghetti wormsSpaghetti worms Occupy burrowsOccupy burrows Parapodia are reduced to grab Parapodia are reduced to grab

sides of burrowsides of burrow Cluster of extensible tentaclesCluster of extensible tentacles

Extend over sediment like Extend over sediment like active spaghettiactive spaghetti

Can be 1 m or more in lengthCan be 1 m or more in length Mucus on tentacles traps Mucus on tentacles traps

particlesparticles AmphitriteAmphitrite

Feather-duster wormsFeather-duster worms Secrete calcareous tubes or Secrete calcareous tubes or

construct from foreign materialsconstruct from foreign materials Crown of tentacles (known as Crown of tentacles (known as

radioles)radioles) One radiole (most dorsal) is One radiole (most dorsal) is

modified and acts as an modified and acts as an operculum when crown is operculum when crown is withdrawnwithdrawn

Suspension feedersSuspension feeders

Beard wormsBeard worms Also called pogonophoransAlso called pogonophorans 80 spp.80 spp. Live deep in ocean; typically Live deep in ocean; typically

near hydrothermal ventsnear hydrothermal vents Up to 1.5 m in lengthUp to 1.5 m in length Prostomium bears beard of Prostomium bears beard of

tentaclestentacles Also live in tubesAlso live in tubes No mouth or anusNo mouth or anus

Symbiotic chemoautotrophic Symbiotic chemoautotrophic (sulfur oxidizing) bacteria live in (sulfur oxidizing) bacteria live in modified gut (trophosome)modified gut (trophosome)