Unit 5.3

Phylum Annelida

MyxozoaMyxozoaMyxozoaMyxozoa

ArthropodaArthropodaArthropodaArthropoda AnnelidaAnnelidaAnnelidaAnnelida

MolluscaMolluscaMolluscaMollusca

LophophoresLophophoresLophophoresLophophores

HemichordataHemichordataHemichordataHemichordata

VertebrataVertebrataVertebrataVertebrata

Other Other pseudocoelomatespseudocoelomates

Other Other pseudocoelomatespseudocoelomates

NematodaNematodaNematodaNematoda

PoriferaPoriferaPoriferaPorifera

CtenophoraCtenophoraCtenophoraCtenophoraCnidariaCnidariaCnidariaCnidaria

PlacozoaPlacozoaPlacozoaPlacozoa

PlatyhelminthesPlatyhelminthesPlatyhelminthesPlatyhelminthesNemerteaNemerteaNemerteaNemertea

CiliophoraCiliophoraCiliophoraCiliophoraSarcomastigophoraSarcomastigophoraSarcomastigophoraSarcomastigophora

MicrosporaMicrosporaMicrosporaMicrosporaApicomplexaApicomplexaApicomplexaApicomplexa

MesozoaMesozoaMesozoaMesozoa

EchinodermataEchinodermataEchinodermataEchinodermata

CrustaceaCrustaceaCrustaceaCrustaceaChelicerataChelicerataChelicerataChelicerata

UniramiaUniramiaUniramiaUniramia

Other ChordataOther ChordataOther ChordataOther Chordata

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Phylum Annelida

• Segmented body– Each segment is called

a metamere

• Each segment contains tiny hairs called setae that are used for various purposes– Absent in leeches

• Coelom (internal body cavity) is divided by septa

Phylum Annelida• Annelids were the first

organisms to develop a closed circulatory system

• Several one-chambered hearts connect vessels on either side of the esophagus and flex via peristalsis as the worm moves

SeptaSepta

ProstomiumProstomium

PygidiumPygidium

Phylum AnnelidaPhylum Annelida

Annelid bodies are divided by septa into repeating segments. Each segment contains their own set of excretory organs called nephridiopores. This attribute is called Metamerism

Annelid larvaAnnelid larvaApical tuftApical tuftApical tuftApical tuft

MouthMouthMouthMouth

AnusAnusAnusAnus

Ciliary bandCiliary bandCiliary bandCiliary band

StomachStomachStomachStomach

Annelid developmentAnnelid development

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Class Polychaeta• Generally marine• Each body segment has a

pair of fleshy protrusions called parapodia

• Parapodia function in locomotion as well as in respiration (think external gills)

• Well developed heads compared to other annelids

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Class Polychaeta

Head

Parapodium

Tentacle

Class PolychaetaPredatory

Class PolychaetaPredatory

JawJawJawJaw

Everted pharynxEverted pharynxEverted pharynxEverted pharynx

EyeEyeEyeEyeCirrusCirrusCirrusCirrus

PalpPalpPalpPalp

TentacleTentacleTentacleTentacle

ParapodiumParapodiumParapodiumParapodium

Class Polychaeta

Class Polychaeta• Epitoky – a

transformation into the breeding form of an organism

• Epitokes are given the task of reproduction

• Some species bud epitokes from the body and remain in their habitat while the epitokes move to the surface to breed

Class Polychaeta• Dioecious• Many species

reproduce en masse at the water’s surface at night

• Moonlight and artificial light attract spawning masses

• The Palolo worm is harvested in Samoa and eaten as a delicacy

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Tube-Dwelling Polychaetes • Tubeworms &

Featherdusters• Defining characteristic

– Gut tissue forms an organ (trophosome) that becomes filled with chemosynthetic bacteria

– Segmentation confined to small rear portion of animal

• Small intriguing class of tube dwelling worms found throughout the worlds oceans

Tube-Dwelling Polychaetes

• The most interesting aspect of tube worms is the lack of a digestive system– Bacteria in the

trophosome fix the chemicals leaving the vents

– The bacteria can occur at concentrations of 10 billion per gram of trophosome tissue

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Burrowing Polychaetes• Lugworms• Castings can be seen

on the beach at low tide• Lives in a U-shaped

burrow in the sand• Eat sand, extract

biological material from the rock, and then expel the castings outside of the burrow

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Free-living Polychaetes• Common sandworms

and fireworms• Use parapodia like little

legs for locomotion• Roam the ocean floors

searching for food• Fireworm setae contain

potent neurotoxins and can cause a painful rash if touched

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Class Oligochaeta• Earthworms• Few setae – very hard to

see hairs compared with polychaetes

• Clitellum – barrel shaped sexual structures near the anterior end of the worm

• No parapodia• Monoecious

Class Oligochaeta• Extremely important

ecologically• Biological – breaks down

organic matter leaving rich, dark soil

• Chemical – frees phosphates for use in plants

• Physical – aerates the soil by digging tunnels that allow air and water to penetrate

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External Structures of an Earthworm

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Internal Structures of an Earthworm

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Class Oligochaeta

• Copulation & fertilization are separate

• Copulation – two earthworms line up with their anterior ends facing each other and exchange sperm

Class Oligochaeta• Fertilization –after the

worms exchange sperm, the clitellum turns bright pink and secretes a chitinous cocoon around the worm

• The worm then wriggles out of the cocoon and deposits its eggs and its partner’s sperm into the cocoon allowing fertilization to take place

• Worms hatch as small adults – no larval stage

Earthworm Reproduction

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Class Hirudinea• Leeches• Anterior & posterior

suckers• Predominately

freshwater, but do occur in all seas and moist soil

• Leeches do not burrow or crawl, they lack parapodia and setae – instead they move like an inchworm

Class Hirudinea• Anterior sucker is small

and contains the mouth– Anterior sucker creates

a wound with saw like jaws

• Leeches drink other animals’ blood, usually vertebrates– Can be carnivores, or

scavengers; leeches are not set in their feeding habits

• Leech saliva contains an anticoagulant that numbs the wound and keeps the blood flowing

Class Hirudinea

• Leeches are simultaneous hermaphrodites that lack a free-living larvae stage

• Fertilization is internal through copulation

• Development occurs in a cocoon similar to the Oligochaetes

The End