Molluscs & Annelids by os8lO1GE

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									  Molluscs & Annelids
Zoology LS2014, Donald Winslow
          3 March 2008,
 Following Hickman, et al., 2008
  Ch. 16 (pp 332-344, 346-357)
       Ch. 17 (pp 363-378)
          Molluscs & Annelids
•   Protostome
•   Spiral cleavage
•   Mosaic development
•   Eucoelomate
•   Schizocoelous coelom formation
•   Many have trochophore larvae
             Phylum Mollusca
•   Coelom usually only around heart
•   Unsegmented with organ systems
•   Trochophore & veliger larvae in many
•   Gills (ctenidia) or lung
•   Circulatory system usually open
•   Variation in body size
•   Mantle, mantle cavity, shell, foot, head
      Molluscan characteristics
•   Radula & odontophore
•   Visceral mass
•   Surface epithelium, cilia & mucous glands
•   Metanephridic kidneys (drain from coelom)
    – Empty liquid waste into mantle cavity
• Usually nerve ring & paired ganglia
• Mostly dioecious
           Phylum Mollusca
•   Classes Caudofoveata & Solenogastres
•   Class Monoplacophora—one shell plate
•   Class Polyplacophora—8 shell plates
•   Class Scaphopoda—tusk shells
•   Class Gastropoda—snails & slugs
•   Class Bivalvia—clams, mussels, etc.
•   Class Cephalopoda—squid, octopus, etc.
            Class Gastropoda
•   Snails w/ coiled or uncoiled shells
•   Slugs w/ no shells
•   Pulmonate land snails & slugs
•   Marine nudibranchs (no shell, “sea slugs”)
•   Poisonous cone shells
•   Conchs, whelks, limpets, abalones
           Class Bivalvia
• Clams, scallops, mussels, oysters
• Zebra mussels, shipworms, giant clams
          Class Cephalopoda
•   Giant squid
•   Cuttlefish
•   Octopus
•   Chambered nautilus
Phylum Annelida
    Developmental characteristics
•   Spiral cleavage & mosaic development
•   Protostome
•   Eucoelomate
•   Schizocoelous coelom formation
•   Segmentation (metamerism)
    – External rings called annuli
    – Few differences between segments
    Morphological characteristics
•   Bilateral symmetry
•   Chitinous setae (bristles)
•   Parapodia in Class Polychaeta
•   Cerebral ganglia
•   2 ventral nerve cords with giant axons
•   Ganglia & lateral branches in each
    segment
    Specialization of annelid head
•   Tactile organs
•   Taste buds
•   Statocysts
•   Photoreceptors
      Annelid circulatory system
•   Closed
•   Dorsal blood vessel pumps blood
•   Aortic arches control blood flow
•   Ventral blood vessel
•   Respiration by skin, gills, or parapodia
     Digestion and excretion
• Complete digestive tract
• Unsegmented digestive tract
• Nephridia in each segment remove waste
  from blood.
       Reproduction of annelids
•   Complete regeneration when injured
•   Monoecious or dioecious sex
•   Trochophore larvae in some taxa
•   Budding in some taxa
     Sections of annelid body
• Prostomium (“head”)
• Somites (“body”)
• Pygidium (“tail”)
           Annelid coelom
• Septa divide coelom and separate
  segments.
• Fluid in coelom provides hydrostatic
  pressure for “hydrostatic skeleton”.
• Epidermis secretes cuticle.
• Peritoneum (visceral & parietal)
• Mesenteries (dorsal & ventral)
           Phylum Annelida
• Class Polychaeta
  – Mostly marine
  – Some tube-dwelling
  – Mostly dioecious (separate sexes)
• Class Oligochaeta
  – Earthworms and other terrestrial & freshwater
    species
• Class Hirudinida—leeches and relatives
      Examples of polychaetes
•   Nereis
•   Eunice viridis—Samoan palolo worm
•   Featherduster worms
•   Chaeopterus
               Earthworms
• Mix, aerate, hydrate, & fertilize soil
• React to many stimuli, learn
• Hermaphroditic, testes, ovaries
• Seminal vesicles, oviducts, seminal
  receptacles
• Clitellum, fertilization in cocoon
• Freshwater oligochaetes with gills
                Leeches
• Ectoparasitic
• Anterior & posterior suckers
• Medicinal uses

								
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