Phylum Annelida

Question 1

Annelids have 3 classes, what are they?

Answer 1

1. Class Oligochaeta
2. Class Hirudinea
3. Class Polychaeta

Question 2

1. Class Oligochaeta

Answer 2

Earthworms > No appendages

Question 3

2. Class Hirudinea

Answer 3

Leeches > No appendages

Question 4

3. Class Polychaeta

Answer 4

Marine and Freshwater worms > Have appendages

Question 5

General Physiology

Terms involved:
Segments
Septa

Answer 5

• Bodies divided into segments that are all very similar.
• Segments are divided by ‘Septa’ >
  (small membranes that divide)
• Segments are marked by circular grooves called ‘Annuli’.
• Also have internal segmentation of/for organs.

Question 6

Describe the locomotion of Annelids.

Answer 6

Annelids move by contracting their Circular
and Longitudinal muscles and to anchor themselves forward they use what’s called ‘Setae bristles’ which they have.

Circular muscles contract:
- Segment lengthens
- Diameter decreases
(Opposite for Longitudinal muscles)

Question 7

Class Polychaeta general overview:
Break down the meaning for ‘Polychaeta’

Clues:
Where are they found?
What feeding methods do they exhibit? (5)

Answer 7

Poly = many / Chaeta = hairs

1. Found in all marine and freshwater benthic habitats
2. Carnivores, Deposit feeders, Suspension feeders, Grazers and Parasites.
3. Great at regenerating body parts and replace missing parts. (Depends on animals energy reserves)
   - Loss of head or appendages is not fatal for Polychaetes

Question 8

Class Polychaeta: Body structure

Terms involved:

Parapodia 
Peristomium 
Setae/Chaetae 
Septa 
Prostomium 
Palp 
Tentacular cirri 
Pharynx 
*Exhibits Cephalization! = Bilateral symmetry

Answer 8

1. Head = Prostomium
   - includes the: antennae, eyes, tentacles, and palps.
   - antennae have sensory organs.
   - the palps may be sensory or can be used as feeding appendages.
   - Some species have one or two pairs of eyes on the prostomium.
2. Appendages = Parapodia (are paired and lateral)
   Pod = foot / Para = like
3. Setae/Chaetae = Hairs on each segment
4. Septa = The membranes which divide the body segments.
5. Peristomium = First true body segment after the head.
   - includes the tentacular cirrus or cirri which they use to gather and sense food.
6. Pharynx
7. Palps are unique head appendages of annelids. They are used either in feeding or as sensory structures, showing a diversity of external morphology, attachment, and position on the head.

Question 9

What is Cephalization?

Answer 9

• The gathering of sensory organs and brain structures in the anterior region.
• Organisms with cephalization will always have Bilateral symmetry.

Question 10

How does new oxygen O2 enter their bodies and carbon dioxide CO2 leave?

Answer 10

Polychaetes have well-developed closed-circuit blood vascular systems.
Functions:
1. Removes wastes, CO2, N (nitrogen) and other metabolites.
2. Brings in O2
***They can have external gills which provide gas exchange as the blood is pumped close to the skin in some species. Others rely on diffusion across the skin.
** Have hearts in each segment.

Question 11

Class Polychaetes: Reproduction

1. Sexual reproduction
   (6) types

Answer 11

Sexual reproduction:
- Adults can be **DIOECIOUS
(Having both the male + female reproductive organs in separate individuals) or

• exhibit **sequential Hermaphroditism!!!!!!!!
  (Both male + female genitalia)
• Broadcast spawning, Copulation, and Epitoky

Question 12

Class Polychaetes: Reproduction

2. Asexual reproduction

Answer 12

Asexual reproduction:

• Budding
• New individuals can bud directly from the adult

Question 13

Class Polychaetes: Reproduction

3. Epitoky

Terms involved: 
Epitoke
Posterior
Parapodia 
Pelagic morph

Answer 13

Epitoky:
- A form of reproduction in some polychaete annelids in which the worms undergo a partial or complete transformation into an epitoke, a pelagic morph capable of sexual reproduction.

Epitoke spawning is when the body or posterior segments of a worm are modified into a gamete carrying machine.
- The posterior segments swim to the surface using the modified parapodia as paddles.
- Eggs and sperm are released into surface waters.
EG: Palolo worms (Samoa)

Question 14

Class Polychaetes: Feeding methods (4)

Answer 14

> Deposit feeding
Non selective deposit feeding
Selective deposit feeding
Suspension feeders