Annelids Flashcards
What type of coelom do annelids have?
They are coelomates so have a true coelom
What are the advantages of having a coelom?
Transport
Gut moves independently of the body wall
Site for gamete maturation
Hydrostatic skeleton
What is a hydrostatic skeleton?
Muscles can contract against the water as it is incompressible
Have circular muscles - long and thin
Have longitudinal muscles - short and fat
Muscles contract alternately
What is metameric segmentation in annelids?
Segments are theoretically identical but have certain names to differentiate between them
The prostomium is the head
The pygidium is the bottom
Proliferation zone is where new segments are formed
The other segments are identical but this can differ between species
What structures run the length of an annelid and which ones are repeated in each segment?
Longitudinal nerves (e.g. ventral nerve cord) and the gut run down the whole animal
The mouth is just in the prostomium
The anus is just in the pygidium
Septa separate the segments - this varies between species (some have developed septa and some have none)
Septa is more developed if the animal uses peristalsis
The nephridium is repeared in each segment
What can annelid segmentation be modified by?
Restriction of structures to particular segments
Some segments develop special structures
Segments may fuse together
Do most annelids have a protonephridium or a metanephridium? How does this work?
Metanephridium
Substances are forced out of the blood vessels and into the coelom
Then transported around
Taken into the metanephridium
This takes up useful products
Discards unwanted and waste products
How can the annelids be organised?
Clitellata - split into the oligochaeta (mainly earthworms) and hirudinea (mainly leaches)
Polychaeta are now split into errantia (often active forms) and sedentaria (often less active forms)
The clitellata have evolved from the sedentaria
Give some features of polychaetes
Some have parapodia - fleshy projections on the side of the body (can be used for exchange, movement, feeding and generating current)
Have lots of setae
Have chaetae on the parapodia that are fixed into position
Prostomium is well developed
What are nuchal organs of annelids used for?
Chemial detection
How do sabella sort particles?
Large particles are thrown out
Medium particles are for tube feeding
Small particles are for feeding
How do polychaetes reproduce?
Mostly dioecious (separate sexes)
Have external fertilisation although some is internal
Spawning may be synchronous
Larval stage is known as a trocophore and has a row of cilia around it
What is epitoky?
Transformation into a reproductive form
Devotes all energy to reproduction (transforms gut) and dies after reproduction
Some have an epitoky region which can bud off the end of the worm and can swim independently of the worm (bundle can be sperm or eggs)
Often matches the lunar cycle
What are some features of the clitellata?
No parapodia
Produce clitellum (glandular area responsible for secretion) and cocoons
Hermaphrodites
Gonads are restricted to a few segments
Give some features of the oligochaetes
Few setae
Well developed septa between segments
Peristaltic locomotion
Gas exchange over body surface (body has to be moist for this)
Can undergo aestivation (when environment gets harsh, can go into a rest stage until it improves)
Briefly explain how oligochaetes reproduce
Pair up head - tail
Clitellum binds worms together
Sperm is released from the male gonopore and travels along the sperm groove
It then transfers to the other worm and enters the spermathecal opening
After separating, the clitellum starts to produce the cocoon
Before the cocoon fully forms, clitellum produces albium (which contains nurtients) for the offspring
