Annelids Flashcards
Invertebrates lecture 2
Which protostome group are annelids in?
Lophotochozoans
What does ‘annelid’ mean?
‘ringed worm’
What are the features of an Annelid’s body?
in terms of segments
> Metamerically segmented
Segments added in front of pygidium
Some have set no. of segments
What are the other features of Annelida bodies?
> Body wall w/ outer circular & inner longitudinal muscle layers
Transparent moist cuticle
Chitinous setae
- often present on parapodia
What does the septum allow?
different muscle groups to do different things
Is their circulatory system ventral or dorsal?
What about their nervous system?
Dorsal
Ventral
How many germ layers do annelids have?
Do they have a coelom?
3
= triploblastic
Yes
= coelomate
What functions as a hydrostatic skeleton?
And what is this used for?
Coelomic fluid
Supplies turgidity
- circular & longitudinal muscles can work against it
What happens when the circular muscles contract?
What about the longitudinal muscles?
Long & thin
Short & fat
Describe annelida blood systems
Closed
Segmentally arranged
Contains respiratory pigments e.g. Hb
Describe annelida digestive systems
Complete
Not metamerically arranged
Describe gas exchange in annelida
Through skin, gills or parapodia
- can be via cuticle & gut too
Describe annelida’s excretory system
Pair of nephridia for each metamere
Describe annelida nervous systems
Double ventral nerve chord & pair of ganglia w/ lateral nerves in each metamere
Describe annelida brains
Pair of dorsal cerebral ganglia w/ connections to cord around oesophagus
Describe annelida sensory systems
Tactile organs
Taste buds
Photoreceptor cells
Eyes w/ lenses
How do annelids reproduce?
Hermaphroditic OR separate sexes
Asexual reproduction by budding in some
What are the 3 main Annelid groups?
Polychaeta (e.g. ragworms)
Oligochaeta (e.g. earthworms)
Hirudinea (e.g. leaches)
How are the 3 Annelid groups related?
Paraphyletic
Oligochaeta derived from Polychaeta
Hirudinea derived from Oligochaeta
What is tagmosis?
Different segments of body carry out different functions
Polychaeta means what?
‘many chetae’
What are the features of Polychaeta?
> Well-differentiated head w/ specialised sense organs
Paired, paddle-like parapodia
Don’t have lophophores but do have trochophores
Separate sexes
- hatch into planktonic larva
- later metamorphose into juvenile annelid
Give an example of a Polychaeta
Neresis
ragworm
What are the 3 different Polychaete life habits?
> Errant = free moving e.g. Neresis & Aphrodite > Sedentary burrowers e.g. Arenicola >Sedentary tube formers - filter feeders e.g. Sabella, Serpulid -nutrition from endosymbiotic bacteria e.g. Riftia pachyptila
Why species example has iridescent chaetae?
Aphrodite aculeata
= a sea mouse
Tube-living, deposit-feeding annelids ingest up to how much of their own body weight a day?
120x
What features do tube-living, filter-feeding annelids have?
> Tentacles w/ respiratory & feeding functions
Light sensors on tentacles detected shadows - pulls tentacles into tube when threatened
Food particles passed via mucus band to back of mouth
What are deep sea hydrothermal vents rich in?
Reduced chemicals e.g. sulphides & methane
Riftia pachyptila has no gut. How does it gain nutrition?
Depends on chemoautotrophic symbiotic bacteria - pack a large organ called trophosome
- -> Hb in gill-like plumes captures H2S from vent + CO2 from water
- -> generates organic carbon using sulphide as e donor & O2 as e acceptor
Give an example of an Oligochaeta
Lumbricus
=Earthworms
What are the key features of Oligochaeta?
> most bear setae
hermaphrodites
clitellum for brooding eggs
predators, detritivores & direct deposit feeders
How do earthworms move?
- contrat circular muscle
- contract longitudinal muscle
- front end bulges out
- push setae out
What are the key features of Hirudinea?
> fixed no. of segments - approx 34 > anterior & posterior suckers > coelom doesn't act as hydrostatic skeleton > no septae or setae > lack parapodia & tentacles
Why doesn’t the coelom in Hirudinea act as a hydrostatic skeleton?
Packed with mesenchyme
What are the medicinal uses of leeches?
> clear up discolouration of black eyes > saliva contains anti-inflammatories - relieve arthritis > used after surgery when reattaching skin flaps - re-establish blood flow
Describe digestion in leeches
> only exopeptidase > slow digestion > no food for <18months > Aeromonas veronii = gut bacteria may contribute to digestion & produce Vit B > Blood in gut doesn't coagulate
Which leech is used in medicine?
Hirudo medicinalis
How do leeches prevent blood clotting?
Calin inhibits platelet adhesion to vessel wall
Decorsin inhibits platelet aggregation
Hirudin inhibits activation of prothrombin
What 3 things does leech salvia contain?
Vosodilator
- dilates blood vessels
Anaesthetic
- reduces chance host feels leech
Antibiotic
- produced by symbiont Aeromonas
