Worms

Question 1

Classification of nematodes?

Answer 1

Roundworms.

Part of Ecdysozoa.

Classified using DNA sequencing.

Question 2

Features of nematodes?

Answer 2

Not segmented, even though they look it. The grooves don’t split up internal organs.

Have a pseudo-coelom. Contains liquid at very high pressures. Organs are suspended in the fluid filled bag.

Only longitudinal muscle.

Criss cross collagen fibres in cuticle (moulting).

Fixed number of cells (eutely).

Question 3

Why are roundworms round?

Answer 3

They have a very high pressure in their body cavity.

Have to have muscles at anus and mouth to control opening and closing.

Question 4

How do nematodes move with only longitudinal muscle?

Answer 4

The two sides of he worm antagonise each other. Sinous body waves. Good for moving through soil, fruit or body tissues, but are bad swimmers.

Question 5

Example of a nematode parasite?

Answer 5

Guinea worm
Africa and S Asia. Adult female can be up to 80cm long. Lives under human skin and forms painful ulcers.

Lifecycle includes phase inside copepod crustacean.

Humans get infected by drinking water with infected copepods.

Question 6

Example of a useful nematode?

Answer 6

C.elegans is used as a model system for studying disease genes, etc.

Programmed cell death was first discovered in C.elegans.

Question 7

Classification of platyhelminthes?

Answer 7

The flatworms.

Part of Lophotrochozoa.

Include:
Free living flatworms
Flukes
Tapeworms

Question 8

Why are flatworms bilateria?

Answer 8

They have 3 germ layers, with mesoderm in the middle.
Bilateral symmetry
CNS with brain

Lack features in other Bilateria:
no body cavity so no hydrostatic skeleton
no gills/respiratory organs or blood system - oxygen must reach cells by diffusion

Question 9

Example of a fluke?

Answer 9

Monogeneans are ecto-parasites on fish.One host for their lifecycle and the ciliated larva swim to new fish.

Question 10

Classification of Annelids?

Answer 10

Part of Lophotrochozoa.

Key character is segmentation.

Includes ragworms, lugworms, fanworms, earthworms and leeches.

Question 11

General features of annelids?

Answer 11

1. Vermiform: worm shaped, much longer than they are wide. Soft bodied.
2. Large coelom: cavity is lined by an epithelial cell layer within the mesoderm (coelom). Big fluid filled space, hydrostatic skeleton. Epithelial cells are the key to animal organisation.
3. Longitudinal and circular muscles
4. Segmentation: Coincident repetition of characters. The muscle, nervous system, excretory system, coelom. Prostomium isn’t segmented.
5. Septa allow the coelom to be segmented. Septa are thin sheets of tissue, which are perforated by the gut and blood vessels.
6. Ventral nerve cord
7. Water permeable skin so annelids are always aquatic or found in wet places on land. Makes it easy for gases to pass through as well
8. Septae are a special kind of bristle.