Chapter 17: Annelids Flashcards
- Annelids exhibit segmentation or metamerism. This means that their body is composed of ?
- Each unit contains what?
- serially repeated units
- components of most organ systems
The evolution of metamerism allowed for what in regards to structure and function?
- greater complexity
Evolution of metamerism pros:
- It increased burrowing efficiency by doing what?
- Regards to the NS?
- Safety factor?
- permitting independent movement of segments
- more sophisticated NS
- if one segment fails others will function perfectly fine
- The type of cleavage they undergo is ?
- The coelom forms via?
- They share a ___ as the ancestral larval form
- The habitats they inhabit? (3)
- spiral mosaic
- schizocoely
- trochophore
- marine, freshwater and moist terrestrial habitats
-Within the annelid phylum / are marine worms.
2/3
Body segments marked by circular grooves are called what?
- annuli
Metamerism :
- Repetition of organs in segments is called what?
- metamere or somites
What separates the segments?
- septa
Segmentation is found in ___, probably homologous with __, and in ___ where it evolved independently.
- arthropods
- annelids
- vertebrates
Describe Setae!
- composition
- absent in what animals of this phylum?
- short setae?
- long setae?
- tiny chitinous bristles
- absent in leaches
- short setae: anchor segments in earthworms, prevent it from slipping backwards
- long: help aquatic worms swim
Habitats of the following classes:
- Polychaetes
- Oligochaetes
- Hirudinea
- primarily marine and usually benthic (bottom dwelling)
- freshwaters, or terrestrial soils….many leaches are predators
Body wall:
- the head is composed of what? (2)
- prostomium
- perstonium
Body wall:
- The terminal portion bearing the anus is called ?
- pygidium
Body wall:
- Are the head and pygidium considered metameres?
no
Body wall:
- New metameres form where?
- just in front of the pygidium
Body wall:
- The surface of an annelid is covered with what?(2)
- epidermis and a thin outer layer of non-chitinous cuticle
Body wall:
What underlies the body wall?? (2)
- strong circular and longitudinal muscles
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?
- schizocoely
- Peritoneum (mesodermal epithellium)
- Peritonea
- gut and longitudinal blood vessels
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
- leeches
- fluid volume
- causes body to shorten and expand
- causes body to narrow and lengthen
- widening and elongation moves the animal
- peristalsis
- undulatory
Origins of Metamerism and the Coelom :
- There is ___ satisfactory explanation for origins of metamerism and coelom has gained acceptance.
no
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.
- hydrostatic skeleton
- circulatory fluid
- gametes
Origins of Metamerism and the Coelom :
- It is unlikely that segmentation is homologous among ___, ___ and ___.
arthropods, annelids and chordates
Origins of Metamerism and the Coelom :
- Current evidence supports the hypothesis that segmentation arose how?
- independently multiple times
- 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 ___.
- burrowing
- arthropods, exoskeleton
Annelids share many developmental features with what other phylum and are presumed to be closely related?
- Molluscs
