Annelids - Segmented Worms Flashcards
Annelids - symmetry / cleavage
Bilateral symmetry
Spiral cleavage
Protostome
Annelids are coelomate, what is their structure?
Triploblastic
Have body cavity
Central gut surrounded by ENDODERM
Two layers of MESODERM (body cavity/coelom between)
Outer layer - ECTODERM
What are the advantages of having a coelom?
Transport - moves materials around the body
The gut moves independently from the body
Acts as a hydrostatic skeleton
Site of gamete maturation
Hydrostatic skeleton
Structure made of fluid
Water is incompressible
Base against muscles which can contract
What is metameric segmentation?
Body is divided into interconnected segments
All identical apart from the head and tail
Head = Prostomium
Tail = Pygidium
Septa - areas between segments
Gut and nervous system goes through all segments
Hydrostatic skeleton (muscles)
Circular muscles - long & thin (co round the animal)
Longitudinal muscles - Short and fat
muscles work antagonistically against one another
Proliferation zone
Where new segments are made
Closed circulatory system
Contains blood vessels
Segmentation modification
Restriction of some structures to particular segments
Some segments can fuse together
Can be specialised for swimming, breathing etc
Excretory system
Metanephridium
How the Metanephridium works
Metanephridium - fluid forced out of blood vessels into coelom by muscular contractions - nutrients is absored and water and waste is then passed out of the animal via the metanephridium
3 groups within annelids
Plolychaeta (mostly marine worms)
Oligochaeta (earthworms)
Hirudinea (leeches)
(these two are grouped into clitellata)
Polychaete - Setae
setae are found on Parapodium (fleshy projections)
Increase surface area
Used for movement and eating
Setae look similar to hairs
polychaete - Prostomium
Very well developed
Different forms of polychaete
Errant (active): E.g. Hag worm (Nereis)
Sedentary: E.g. Tube worm (sebella)
