Annelida

Question 1

Features of Annelida

Answer 1

Coelomate animals
-2 layers of mesoderm, which line the ecto and endoderm 
-cavity in middle = coelom 
-usually fluid filled
Metameric segmentation
Nephridia

Question 2

Advantages of coelom

Answer 2

+Useful in transport of nutrients and gas (in coelomic fluid)
+Gut moves independently of body wall
+Acts as a site for gamete maturation
+Fluid inside can act as hydrostatic skeleton - as don’t have normal one
can then be more rigid
provides firm base for muscle contraction

Question 3

Movement in annelids

Answer 3

2 types of muscle:
1. Circular - squeeze inwards = long and thin animal
2. Longitudinal - contraction shortens animal (short & fat)
Work antagonistically
Animal moves by peristalsis
Waves of contractions in 2 different muscles causes movement
Contractions can be specific to individual segments = precise and efficient movement

Question 4

Metameric segmentation

Answer 4

Functioning units that form animal
Same as each other except prostomium (head) and pygidium (tail end)
Proliferation zone near tail where new form
Septa divide each segment (varies as to whether present, can be well developed too)

Question 5

Annelid general body structure

Answer 5

Gut runs through animal
Head has mouth and tail has anus
NS runs through animal, conc of nervous tissue at anterior
Ventral nerve cord runs throughout
Nephridium openings into each segment
Closed circulatory system - blood vessels

Question 6

Modification of segments

Answer 6

Reproductive tissue found in some and not others
-some structures restricted to certain segments
Can develop features for feeding or protection
Some fuse together to form bigger - like the head

Question 7

Nephridia

Answer 7

Excretory organ
metanephridium - high pressure
1. Fluid forced through blood vessel walls from muscle contractions into coelomic fluid
2. Makes way into metanephridium
3. Useful substances absorbed
4. Waste passed out