BIOL 111 Lecture Notes - Lecture 43: Hydrostatic Skeleton, Annelid, Seta

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23 Jul 2016
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BIOL 111 Organismal Biology
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Annelids
!phylum of segmented worms
!annelid” = little rings
!there are more than 15000 species
!they are found in moist terrestrial or aquatic environments
!they grow between 0.5 mm 3 m in length
!they are lophtrochozoans
!they are coelomates
!EVOLUTIONARY INNOVATION: segmentation
o!segmentation can be regular (e.g. earthworms or centipedes) or irregular (e.g.
lobster, ticks)
Segmentation
!segmentation has evolved with annelids, and with the exception of one group, has
followed through all the way to chordates
!advantages of segmentation:
o!allows for multiple copies of organs and structures
o!allows for efficient nervous control
!!ganglia can form in each segment
!!this facilitates faster nervous responses
o!modification of segments
o!better control of movement
o!increases body size by unit repetition
!regional differentiationsegments are similar, but each can be modified
o!e.g. differentiation of the gut (digestive tract)
!each segment is covered externally by epidermis, then moving inward, circular muscles,
longitudinal muscles, and then the coelom
Annelid Locomotion
!each segment has circular muscles, longitudinal muscles (that run along the length of
worm), and coelomic space (which is used as a hydrostatic skeleton)
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