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Unit 5.3
Phylum Annelida
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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
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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
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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
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Annelid larvaAnnelid larvaApical tuftApical tuftApical tuftApical tuft
MouthMouthMouthMouth
AnusAnusAnusAnus
Ciliary bandCiliary bandCiliary bandCiliary band
StomachStomachStomachStomach
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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
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Class PolychaetaPredatory
Class PolychaetaPredatory
JawJawJawJaw
Everted pharynxEverted pharynxEverted pharynxEverted pharynx
EyeEyeEyeEyeCirrusCirrusCirrusCirrus
PalpPalpPalpPalp
TentacleTentacleTentacleTentacle
ParapodiumParapodiumParapodiumParapodium
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Class Polychaeta
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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
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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
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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
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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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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
External Structures of an Earthworm
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
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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
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Earthworm Reproduction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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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
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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
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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
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The End