BIO2231 Lecture Notes - Lecture 8: Peristomium, Prostomium, Body Cavity
Lecture 8 – Annelids (segmented worms)
Metamerism (segmentation)
• Annelids
o Show most elaborate form of segmentation
• Both external and internal features (all occur in each segment)
o Coelom
o Musculator
o Parapodia and setae
o Blood vessel
o Nerve and ganglia
o Metanephridia
o Reproductive organs
o Gut isn’t segmented
Phylum Annelida
• Marine, freshwater and semi-terrestrial
• Spiral cleavage
Features
• Body Structure
o Inner body wall lined by thin mesodermal sheet,
peritoneum
o Visceral organs lined by serosa
o Suspending sheets, mesenteries
o Body wall muscles act on fluid → facilitate
movement
• Highly developed coelom
o Facilitates more effective digestive system
• Metamerism
o Highly developed
o Segments are arranged in linear series and marked by circular rings,
annuli
o Increases the effectiveness of coelom for movement
▪ But decreases efficiency of diffusion (separated by tissue)
o Harder to move nutrients in absence of circulatory system which
annelids have
o Each segment has its own copy of body organs, repetitively arranged
▪ Segments largely function independently from eachother
o More efficient locomotion: hydrostatic pressure
o Lessened impact of bodily injury
o Tagmatization
▪ Ability to devote certain segments of the body to specialised
functions
• Prostomium
o Contains sense organs
▪ Eyes
▪ Tentacles
• Segmented trunk
o Serially repetitive
o First segment is peristomium (contains pharynx)
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Document Summary
Metamerism (segmentation: annelids, show most elaborate form of segmentation, both external and internal features (all occur in each segment, coelom, musculator, parapodia and setae, blood vessel, nerve and ganglia, metanephridia, reproductive organs, gut isn"t segmented. Phylum annelida: marine, freshwater and semi-terrestrial, spiral cleavage. Setae: small chitinous bristles which project from the body of annelids, can be attached to extensions of body parapodia, enables worm to pull itself across surface, hooked into surface (protruded) Circulation: closed circulatory system, muscular blood vessels and aortic blood vessels for pumping, each segment has its own heart, respiratory pigments (haemoglobin) Nervous system: pair of dorsal cerebral ganglia act as brain, double longitudinal ventral nerve chords, pair of fused ganglia on nerve chord in each segment. Reproduction: asexual and sexual (both, hermaphroditic (both sexes in same organ) or separate sexes, spawn via metanephridia, fertilisation produces a trochophore larva, larvae present.
