L8 Annelids Flashcards
What type of body cavity do they have?
Coelom - are coelomates
What are the advantages of having a coelom?
Transport substances
Gut can move independent of the body wall
Site for gamete maturation
Acts as a hydrostatic skeleton
How does the coelom act as a hydrostatic skeleton?
Filled with fluid - incompressible. Circular muscles go around the animal, and longitudinal muscles run down it, they can move antagonistically, which allows the animal to move by peristalsis
What is metameric segregation?
Functioning units that form the animal, most are similar
What is the proliferation zone?
Where new segments occur
How is segmentation modified?
Structures may be restricted to a particular segment
Some segments develop specialised structures
Segments fuse
What is the prostomium?
the first body segment in an annelid worm’s body in the anterior end
What is the pygidium?
Terminal segment of certain invertebrates
What forms the brain in annelids?
The ventral nerve cord ends in a cone of nerves at the anterior end
What are septa?
Divisions internally between the segment - depends on group how well formed they are, or if present at all
What are nephridium?
Used in excretion - is a tubule opening to the exterior of the animal at each segment
What are the three classes of annelids?
Polychaetas
Oligochaetas
Hirudinea
Which class is most diverged?
Hirudinea
What are the general characteristics of the polychaetes?
Lots of setae
Parapodia
How many species of polychaetes are there?
around 8000, mostly marine segmented worms e.g. fan worms, tube worms
What are setae?
a stiff structure resembling a hair or a bristle, especially in an invertebrate
What are parapodia?
A number of paired muscular bristle-bearing appendages used in locomotion, sensation, or respiration
Give an example of a sessile form
Fan worm, has a head specialised for collecting food
Give an example of an errant (mobile) form
ragwort, move around a lot, so have developed parapodia. Are active hunters so require jaw like structure
Give an example of a sedentary form
Arenicola, lugworm. Used as fishing bait parapodia are reduced, as are burrowers. Are deposit feeders, living in u shared burrows. essential to ecosystem as they ensure the movement and recycling of organic material in the sand
how do polychaetes reproduce?
Dioecious External fertilisation Spawning may be synchronous Epitoky Produce trochophore larvae Swarming
What is epitoky?
A transformation undergone before reproduction, that occurs in many species. Requires a lot of energy,
What are the clitellata?
The hirudineans and the oligochaetes
What are the general features shared by the clitellata?
No parapodia
Produce clitellum
Hermaphrodite
Gonads are restricted
What are the oligochaete, and what are their general characteristics?
eg. Earth worms, have different ecotypes
are terrestrial and freshwater
Few setae, but have very well developed septre
Peristaltic locomotion
deposit feeder
Gas exchange across the skin so vulnerable to predation
mutual sperm transfer
What did Darwin show in his earthworm studies?
Are an essential part of soil nutrient cycling, Bunged burrow with leaves, worms dragged the leaves down the burrow from the narrow end, displaying some sort of intelligence
What are the Hirudineans and what are their general characteristics?
Leeches, are the most advanced annelids
no setae
restricted to 34 segments
Mutual sperm transfer
Have a sucker on first and last segments
Suckers and longitudinal muscles used to move
Predacious, of insects and vertebrates, penetrate with a proboscis - can take up to 10 times body weight in blood
