Annelids (Polychaeta)

Question 1

What are the main features of annelida?

Answer 1

Bilateral symmetry
Septa
Cephalization
Setae
Complex digestive system
Close circulatory system
Epidermis is the primary gas exchange organ
Ganglia and longitudinal nerve cords
Separate sexes or hermaphrodites
All environments
Triploblastic

Question 2

What are the 6 classes of Annelid? And what problems do we face classifying annelids?

Answer 2

Polychaeta - bristle worms
Oligochaeta - earthworms
Hirudinida - leeches
Siblonglinidae - beard worms
Echiura - spoon worms
Sipuncula - peanut worms

Cryptic speciation (few morphological differences)

Question 3

How is the true coelum formed?

Answer 3

By splitting the mesoderm

Question 4

What are the advantages of a coelum?

Answer 4

Transport
Reproduction
Locomotion - muscles can contract against it

Question 5

Annelids have fine control of movement because they can independently move separate segments. How?

Answer 5

Contraction of circular muscle = body elongates
Contraction of longitudinal muscle = body expands
They also have chitinous setae that grip surrounding sediment and drag the body along

Question 6

What are some defining characteristics of Polychaeta?

Answer 6

Many setae
Paire appendages (paddle-like parapodia) enable swimming)
Mandibles
Well differentiated head with specialised sense organs
Errant polychaeta have a evertible pharynx

Question 7

Hoe do polychaeta feed?

Answer 7

Some species are predatory

Some filter-feed

Question 8

Discuss the reproduction of Polychaetes

Answer 8

Asexual fragmentation and regeneration - each segment that breaks off grows a new head and tail by proliferation

Sexual (epitoky) - worms undergo transformation into an epitoke, a morph capable of sexual reproduction. Here gametes are produced
Epigamy - Whole worm transforms into a swarming epitoke, after reproduction, it dies
Schizogamy - the sexual forms are budded from the posterior