Phylum Annelida – The Annelids (Segmented Worms)

Phylum Annelida Segmented Worms Leech Christmas tree worm Fireworm Feather duster worm

Figure 33.24 Annelids, the segmented worms: Polychaete (left), feather-duster worm (middle), leech (right)

Figure 33.24cx Christmas-tree worms

Annelids SEGMENTATION! Closed circulatory system Alimentary canal Five pairs of hearts Gas exchange across skin Metanephridia for gas exchange Nitrogenous wastes exit from each segment through pores Nervous system with ganglia and ventral nerve cords

Figure 33.23 Anatomy of an earthworm

Three classes: Oligochaetes Earthworms Polychaetes: Fanworms Tube dwellers (marine) Hirudinea: Leeches Used to treat bruised tissues and to stimulate circulation

Table 33.4 Classes of Phylum Annelida

Annelid Systems Complete digestive tract - some specialization - crop and gizzard Closed circulatory system - is segmentally arranged dorsal and ventral vessels aortic arches (hearts)

The closed circulatory system is much more efficient!

Respiration across body surfaces some have gills some use parapodia

Nervous system ladder shaped pair of cerebral ganglia double ventral nerve cords pair of ganglia in each segment several sensory structures taste buds tactile organs eyes in some statocyst

Reproduction some are monoecious, others dioecious some have asexual reproduction by Budding or Fragmentation

Class Polychaeta (“many bristles”) Make up 2/3 of phylum most primitive annelids; ancestral to other two classes almost all are marine, few freshwater species External sexual fertilization

Class Oligochaeta “some bristles” Spacious coelom Live typically on land Developed sensory organs but no eyes – clitellum used as copulatory organ; cocoon forms here Reproduce by hermaphroditic sexual reproduction

Figure 33.23x External anatomy of an earthworm Class Oligochaeta Clitellum

Class Oligochaeta Digestive System - well differentiated mouth pharynx crop gizzard intestine – Typhlosole increases surface area anus

Class – Hirudinea Ex: leeches Freshwater or terrestrial Have suckers Segmentation fixed Clitellum only during season Digestive tract large crop Anticoagulant in saliva Medically important

Why we all  love worms… They burrow in the ground allowing for air flow and water flow (keeps the ground aerated and moist) Their waste fertilizes the soil we use Many are detritivores; they eat dead material so we aren’t buried by it They have been proven to promote plant growth AND research has shown worms reduce the speed of erosion Leeches have been used for centuries for medicinal purposes – even today they are used for their natural anti-coagulants to promote the growth of new capillaries so that tissue does not die after surgery