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)
Polychaete Reproduction
Dioecious (seperate sexes) (mostly)
External fertilisation
Spawning may be synchronous
Larval stage (trochophore)
Ciliated larvae
Polychaetes - Epitoky
Transforms body into a reproductive form
Devotes all energy into reproduction
Irreversible body transformation
Some produce epitokes (gamete pouches)
Clitellata (Oligochaetes and Hirunineans)
No Parapodia
Produce clitellum & cocoons
Hermaphrodite
Gonads restricted to a few segments
What is a clitellum?
Used in reproduction to fuse together in mutual exchange of sperm
Produces cocoon
No larval stage
Oligochaetes (earthworms)
Very few setae
Peristaltic locomotion
- well developed septa
Gas exchange over body surface
- need to stay moist
Earthworm (oligochaetes) ecotypes - behaviour alterations
live in burrows
when its dry they move deeper into the burrow
come up to surface when its wet
Aestivation - stress response to high temps (hibernation).
Darwins work on earthworms
Showed how important for nutrient recycling they were
Also tested their intelligence
How they pulled material into their burrow
e.g. pull in by the easiest point
Reproduction in Earthworms (oligochaetes)
Mutual exchange of sperm
Worms pair up - head to tail
Sperm is released from male gonopore and travels down the worms body and is then passed over to the other worm into the spermathecal opening
Forms cocoon that picks up eggs and sperm
Oligochaetes
Earthworms
Hirudineans
Leeches
Hirudineans structure
No setae
Dorsoventrally flattened
Suckers as both ends
Restricted number of segments
How many segments do leeches have
34
Hirudineans (leeches) reproduction
Mutal exchange of sperm - clitella
Produce cocoons
Some brood young and show parental care
Leeches movement
Crawl with suckers
waves of muscular contractions
Leeches are predaceous
Proboscis / jaws
Eat other small invert
Blood suckers
