1: Annelids

Question 1

What are annelids known as?

Answer 1

Segmented worms

Question 2

The annelids are coelomates, describe this.

Answer 2

They have a body cavity (coelom) between their ectoderm (surface) and mesoderm

Question 3

What are the advantages of having a coelom?

Answer 3

Transport
Gut moves independently of body wall
Site for gamete maturation
Hydrostatic skeleton

Question 4

Describe the hydrostatic skeleton of the Annelids

Answer 4

• Water incompressible → base against which muscles can contract
• Circular muscles - when contracted worm is long & thin
• Longitudinal muscles - when is contracted worm is short & fat
  Antagonistic muscles

Question 5

Describe how the Annelids move

Answer 5

Peristalsis → Waves of contraction by longitudinal/ circular muscles

Metameric segmentation makes this more efficent and precise

Question 6

What sort of segmentation is found in Annelids?

Answer 6

Metameric: the body is divided into interconnected segments

Question 7

What is the ‘head end’ known as in Annelids?

Answer 7

Prostomium

Question 8

What is the ‘tail end’ known as in Annelids?

Answer 8

Pygidium

Question 9

Where are new body segments formed in Annelids?

Answer 9

Proliferation zone

Question 10

What structure divides the segments in Annelids?

Answer 10

The septum

Question 11

Describe the excretory system in annelids

Answer 11

Metanephridium:
Fluid forced out of blood vessels by muscular contraction, it floats around in the coelom
Goes through metanephridium
Useful substances reabsorbed
Waste passed out through gut

Question 12

Describe the Polychaeta

Answer 12

• Largest group within the annelids
• Predominantly marine worms

Question 13

Describe the general body plan of the polychaetes

Answer 13

• Parapodia → fleshy projections, have various functions
• Paradodia covered in lots of setae → hairy things
• Prostomium well developed:
  In predacious form → protruding jaw, eyes, nuchal organs (sense chemical cues)

Question 14

Give an example of an errant form of Polychaeta

Answer 14

Nereis (ragworm):
Well developed parapodia
Predacious head

Question 15

Give an example of a sedentary form of Polychaeta

Answer 15

Arenicola (lugworm):
Burrowers
Reduced parapodia
Feed on mud, extract organic material and excrete waste
Live in U shaped burrow, draw sand in, back up burrow = worm cast

Question 16

Describe Polychaete reproduction

Answer 16

• Mostly dioecious (separate sexes)
• External fertilisation (due to marine environ)
• Larval stage (trochophore) → like molluscs
• Spawning may be synchronous
• Body transformed by epitoky into reproductive form.
  E.g Males form elaborate parapodia for swimming around
  E.g Epitokes (packets of gametes) form at the end of the worm and bud off

Question 17

Very generally describe the Clitellata (oligochaetes & hirudineans)

Answer 17

No parapodia
Produce clitellum & cocoons
No larval stage!
Hermaphrodite
Gonads restricted to a few segments

Question 18

What are the Oligochaetes known as?

Answer 18

Earthworms

Question 19

Describe the Oligochaetes

Answer 19

• Peristaltic locomotion = well developed septa between segments
• Gas exchange over body surface → must be damp, can produce mucus if terrestrial

Question 20

What is aestivation in Earth worms?

Answer 20

Dry environ triggers a stress response called aestivation (resting stage)

Question 21

Describe reproduction in the Oligochaetes

Answer 21

Hermaphrodites: mutual exchange of sperm
Clitellum important for repro
1. Earthworms pair up head to tail
2. Clitellum of each worm produces mucus and binds worms together
3. Male gonopore produces sperm which travels down to the other worms spermathecal opening
4. 2 worms separate, mucus formed by clitellum forms the cocoon at top of head
5. Within cocoon fertilisation takes place, mini worms hatch out (no larval stage)

Question 22

Describe the Hirudineans

Answer 22

• No setae, dorsoventrally flattened
• Restricted no. of segments (34)
• Suckers

Question 23

What are the Hirudineans also known as?

Answer 23

Leeches

Question 24

Describe repro and parental care in the Hirudineans

Answer 24

• Mutual sperm transfer
• Sometimes hypodermic impregnation
• Produce cocoons which develop into mini leeches
• Some brood young and show parental care
• Some even have a pouch that they keep their young in

Question 25

Describe locomotion in the Hirudineans

Answer 25

No septa, crawl with suckers
They have lost the septa (earthworms) that allows peristalsis
Still get waves of muscular contractions though

Locomotion in Hirudineans

Question 26

Describe the predacious nature of the Hirudineans

Answer 26

• Proboscis/ jaws
• Some feed on small inverts:
  Swallowed whole
  Suck out hemolymph
• Most regarded as parasitic: blood suckers latch onto vertebrates
• Produce coagulant → hirudin
• Can take up to about 5-10x body weight in blood
• Symbiotic bacteria in gut to aid digestion
• Once they have a good meal they don’t need to feed for another 6 months!

Question 27

Compare the protonephridia with the metanephridia

Answer 27

• Protonephridia have a single opening to the outside environment.
• Metanephridia have two openings, one to the coelomic cavity and the other to the outside
• Proto considered more primitive
• Protonephridia consist of flame cells and tubules.
  Metanephridia consist of tubules and ciliated funnels