Chapter 17: Annelids

Question 1

• Annelids exhibit segmentation or metamerism. This means that their body is composed of ?
• Each unit contains what?

Answer 1

• serially repeated units

- components of most organ systems

Question 2

The evolution of metamerism allowed for what in regards to structure and function?

Answer 2

• greater complexity

Question 3

Evolution of metamerism pros:

• It increased burrowing efficiency by doing what?
• Regards to the NS?
• Safety factor?

Answer 3

• permitting independent movement of segments
• more sophisticated NS
• if one segment fails others will function perfectly fine

Question 4

• The type of cleavage they undergo is ?
• The coelom forms via?
• They share a ___ as the ancestral larval form
• The habitats they inhabit? (3)

Answer 4

• spiral mosaic
• schizocoely
• trochophore
• marine, freshwater and moist terrestrial habitats

Question 5

-Within the annelid phylum / are marine worms.

Answer 5

2/3

Question 6

Body segments marked by circular grooves are called what?

Answer 6

• annuli

Question 7

Metamerism :

- Repetition of organs in segments is called what?

Answer 7

• metamere or somites

Question 8

What separates the segments?

Answer 8

• septa

Question 9

Segmentation is found in ___, probably homologous with __, and in ___ where it evolved independently.

Answer 9

• arthropods
• annelids
• vertebrates

Question 10

Describe Setae!

• composition
• absent in what animals of this phylum?
• short setae?
• long setae?

Answer 10

• tiny chitinous bristles
• absent in leaches
• short setae: anchor segments in earthworms, prevent it from slipping backwards
• long: help aquatic worms swim

Question 11

Habitats of the following classes:

• Polychaetes
• Oligochaetes
• Hirudinea

Answer 11

• primarily marine and usually benthic (bottom dwelling)

- freshwaters, or terrestrial soils….many leaches are predators

Question 12

Body wall:

- the head is composed of what? (2)

Answer 12

• prostomium

- perstonium

Question 13

Body wall:

- The terminal portion bearing the anus is called ?

Answer 13

• pygidium

Question 14

Body wall:

- Are the head and pygidium considered metameres?

Answer 14

no

Question 15

Body wall:

- New metameres form where?

Answer 15

• just in front of the pygidium

Question 16

Body wall:

- The surface of an annelid is covered with what?(2)

Answer 16

• epidermis and a thin outer layer of non-chitinous cuticle

Question 17

Body wall:

What underlies the body wall?? (2)

Answer 17

• strong circular and longitudinal muscles

Question 18

Coelom?

• forms by?
• What lines body wall and forms dorsal and ventral mesenteries ?
• _____ of adjacent segments meet’s to form the septa
• What two things extend through the septa?

Answer 18

• schizocoely
• Peritoneum (mesodermal epithellium)
• Peritonea
• gut and longitudinal blood vessels

Question 19

Hydroskeleton:

• what organisms do not a coelom filled with fluid that serves as a hydrostatic skeleton?
• ____ remains constant
• Contractions of the longitudinal muscles does what?
• Contractions of the circular muscles does what?
• By separating this force into sections what occurs?
• Alternate waves of contractions or ___ allow efficient burrowing
• swimming annelids use ___movements

Answer 19

• leeches
• fluid volume
• causes body to shorten and expand
• causes body to narrow and lengthen
• widening and elongation moves the animal
• peristalsis
• undulatory

Question 20

Origins of Metamerism and the Coelom :

- There is ___ satisfactory explanation for origins of metamerism and coelom has gained acceptance.

Answer 20

no

Question 21

Origins of Metamerism and the Coelom :

• The coelom may have been advantageous as a ____.
• The coelomic fluid would have acted as ____ and reduced need for female cells everywhere.
• The coelom could store ___ for timed release but would require nervous and endocrine control.

Answer 21

• hydrostatic skeleton
• circulatory fluid
• gametes

Question 22

Origins of Metamerism and the Coelom :

- It is unlikely that segmentation is homologous among ___, ___ and ___.

Answer 22

arthropods, annelids and chordates

Question 23

Origins of Metamerism and the Coelom :

- Current evidence supports the hypothesis that segmentation arose how?

Answer 23

• independently multiple times

Question 24

• Selective advantage of a segmented body for annelids appears to lie in the efficiency of ____.
• However this does not explain segmentation in ___ given the rigidity of the ___.

Answer 24

• burrowing

- arthropods, exoskeleton

Question 25

Annelids share many developmental features with what other phylum and are presumed to be closely related?

Answer 25

- Molluscs