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Phylum Platyhelminthes (flatworms)
- acoelomate
- -triploblastic but lack fluid filled body cavity
- no special system for circulation or gas exchange
- lack complete digestive system (have mouth and lumen (space) but no anus)
- -parasitic lack mouth and guts
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what are the two types of flatworms?
- free-living flatworms (class turbellaria)
- tapeworms (class Cestoidea)
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Features of class Turbellaria (free living flatworms)
- mostly marine and predatory
- epidermis covered in cilia
- pair of ventral nerve cords
- pair of ganglia that act as brain near front
- no anal opening, undigested food ejected through mouth
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Class Cestoidea (tapeworms)
- endoparasitic (mostly in vertebrates, invertebrates act as intermediate host)
- no digestive system, absorb nutrients
- scolex for holding onto host's gut
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What are proglottids?
- behind tapeworms scolex (for attaching), long chain of units for reproduction
- produced at base of scolex
- mature proglottids at tail end and are filled with eggs
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Life cycle of a tapeworm
- Need at least 2 hosts
- eggs are ingested by the intermediate host where they grow into larvae go into muscles
- the final host consumes the intermediate hose where they develop into an adult
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What is a definitive host?
the host where the parasite undergoes sexual reproduction
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Class Trematoda (phylum platyhelminthes)
-Flukes
- complex life cycle (at least 2 hosts)
- -adults are parasites in vertebrates, invertebrates act as an intermediate host
- "swimmers itch"
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Phylum Brachiopoda- lamp shells
- true coelem
- attach to substrate with a rubbery stalk
- complete gut with anal opening
- use paired lophophores for suspension feeding
- mainly in deep waters
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Phylum Ectoprocta "moss animals"
- invertebrate
- tough exoskeleton - important for building reefs
- colonial (live close together)
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Phylum Annelida
sea worms, earthworms and leeches
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Annelid characteristics
- segmented, segments separated by septa
- eucoelomate-body cavity is lined with mesodermally derived tissues
- closed circulatory system
- complete digestive system w/anus
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Class Polychaeta (sea worms)
- mainly marine
- body segments have fleshy lobes (contain chaetae)
- clearly differentiated head
- some sedentary, some errant (predatory)
- free-spawning, fertilization occurs outside of parent
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Class Oligochaeta
- less diverse than polychaetes
- lack parapodia and well developed head
- ingest substrate
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Oligochaeta reproduction
- hermaphrodites
- each worm acts as both male and female and implant sperm in each others seminal receptacle
- clitellum secrete gelatinous cocoon, egg is deposited into cocoon, cocoon slides along worm and sperm is also deposited
- fertilization is external
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Class Hirudinea (leeches)
- mostly freshwater but a few marine and terrestrial
- lack chaetae
- have clitellum
- secrete anticoagulent and anaesthetic
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Phylum Mollusca (snails, clams, squids)
- mainly marine
- characterized by calcareous shell (secreted by the mantle-thin layer) covering soft body
- muscular ventral foot is used for movement
- organs are in visceral mass above foot
- radula acts as mouth (convyer belt)
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Class Gastropoda (snails)
- muscular contraction of large foot for movement
- mainly marine
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How do Gastropoda (snails) breath?
lungs rather than gills
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What do shelled snails undergo during development?
torsion- visceral mass twists causing anal cavity to be over head
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What is a visceral mass?
soft non-muscular region of molluscs containing organs
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What are Nudibranchs?
- sea slugs
- steal defenses of cnidarians (jellyfish etc)
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Characteristics of class Bivalvia (clams, oysters, and scallops)
- mostly marine
- feed by filtering water through gills
- some are sessile
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Definition of sessile
fixed in one place
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Class Cephalopoda (squids, cuttlefish, octopuses)-Phylum Molluscs
- tentacles arranged around mouth
- no external shell
- all predatory
- only mollusc with closed circulatory system
- excellent vision
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Cephalopoda development
- octopus exhibit maternal care
- direct development
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