PHYLUM QUIZ

• Phylum Annelida


  The Segmented Worms

  
• Annelida


  From the Latin word annelus meaning "little ring"
• Annelida


  • Earthworms
  • Freshwater worms
  • Leeches
  • Marine worms

  
• Annelida


  • All are segmented worms
  • Approximately 15,000 species

  
• Annelida


  • Triploblastic- 3 cell layers
  • Cephalization
  • Bilateral Symmetry
  • Highest level of organization: organs
  • Eucoelomate
• Eucoelomate


  Have a "true" body cavity that is completely surrounded by mesoderm
• Coelom


  • Closed, fluid filled cavity that surrounds the gut
  • The fluid within acts as a circulatory system (blood)
  • Tissue membranes (mesenteries) suspend organs in the coelom
• Metamerism


  • The body is made up of a series of repeating, coordinated segments called metameres that are separated from one another by septa
  • Each metamere contains sets of repeating organs
• Annelid body


  • Two part head consisting of Prostomium and Peristomium
  • Annuli: circular rings
  • Pygidium: the last segment; where the anus is
  • Clitellum: reproductive structure
• Annelid nervous system


  • 2 cerebral ganglia
  • A ventral nerve cord with 2 ganglia per metamere
  • Some species have sensory organs such as eyes, palps, and tentacles
• Annelid locomotion


  • Both longitudinal and circular muscles which allow them to "wiggle"
  • Most have setae (chitinous bristles secreted by the epidermis) that aid in locomotion and burrowing
  • Fluid in coelom acts as a hydrostatic skeleton
• Annelid gas exchange


  • Mainly by diffusion through skin
  • Class Polychaeta often has specialized structures for gas exchange (e.g. parapodia, gills)
• Annelid digestive system


  • Unidirectional
  • Regional specialization (digestive organs)
• Annelid circulatory system


  • Closed circulatory system composed of blood vessels (some of which are contractile and act as "hearts")
  • Some circulation is also accomplished by the coelomic fluid
• Annelid excretion


  • Excretion is accomplished by organs called nephridia (singular nephridium)
• Annelid reproduction


  • Asexual (budding or fission), and sexual
• Class Polychaeta


  • All marine
  • Contains 2/3 of all known Annelids
  • Common species are clamworms, sandworms, and lugworms
  • Have a well developed head with specialized sense organs
• Polychaeta


  • Commonly called "bristle worms"
  • Have many setae (chitinous bristles secreted by the epidermis) arranged in bundles on paddle-like appendages called parapodia

  
• Parapodium


  Function in gas exchange, locomotion, and feeding
• Tagmatization (tagmosis)


  The fusion and specialization of formerly metameric segments
• Polychaeta


  • Many are filter-feeders with specialized structures
  • Many are predatory with specialized structures
  • Many construct their own homes out of CaCO3 or sand debris and mucous
• Polychaeta reproduction


  • Usually dioecious (separate male and female)
  • No permanent sex organs; gametes are shed into coelom where they stay until time for fertilization
  • Fertilization is usually external in water
  • Indirect development - trocophore larvae swims around until it grows into adult form by adding segments
• Polychaeta defense


  • Some have tubes to hide in
  • Some have vicious jaws
  • Some have modified "stinging" setae

  
• Some Polychaetes have a mutualistic relationship with their host, such as scale worms found near, or in the mouth, of brittle stars, starfish, and sea urchins
• Class Oligochaeta


  • Habitats: terrestrial, freshwater, and marine
  • Have few setae (Oligo = few, chaeta = setae)
• What do earthworms eat?

  • Usually feed on detritus (decaying organic matter)
  • Can feed on dead leaves and plant roots, living things such as other worms, bacteria, and fungi, and decomposing remains of other animals
• Earthworms consume dirt as they burrow, but they do not get nutrients from the dirt - their nutrients come from decaying plant and animal remains that are in the dirt
• Earthworm digestive system


  • Specialized to obtain the maximum amount of nutrients out of the detritus, e.g. pharynx, crop, gizzard
• Earthworm locomotion


  • Circular muscle contraction and longitudinal muscle contraction
• Earthworm reproduction


  • Usually monoecious, still have to have a partner to cross-fertilize by exchanging sperm
• Earthworms are essential soil aerators, mixing the soil with their tunnels and providing fertilizer through their feces
• Class Hirudinea


  • Includes leeches
  • Usually freshwater but there are some marine and terrestrial species
  • No septa between metameres
  • No setae or parapodia
  • Have 2 suckers

  
• Hirudinea


  • Have an extendable proboscis for feeding
  • Usually have a fixed number of segments (34)
  • Each metamere consists of several annuli
• Hirudinea locomotion


  • Lack septa between metameres, so they are incapable of moving like Oligochaetes - instead, they use their anterior and posterior suckers to move
• Hirudinea reproduction


  • Usually monoecious, cross-fertilize by exchanging sperm
• Although some leeches are parasitic blood suckers, many are predators
• Leeches have been used medicinally since the 19th century, currently used to increase blood flow following reconstructive surgery, and their salivary glands contain the powerful anticoagulant hirudin