bi451 2008 pp20 mollusca compressed by c0z1Mq7


									Invertebrate Zoology

Lecture 20: Phylum Mollusca
General; Cephalopoda focus
              Lecture outline
 Phylum Mollusca
  Evolutionary relationships
  Bauplan Basics
  Body systems (briefly…)
      Feeding/digestion
      Circulation/gas exchange
      Osmoregulation/excretion
      Nervous system/sensory
      Reproduction
 Focus: Class Cephalopda
  Cephalopoda diversity
  Evolution of cephalopods
    Class Polyplacophora:
        “many plates”
 The chitons
           Class Gastropoda
 Snails, slugs, nudibranchs et al.
          Class Bivalvia:
           “two valves”
 Clams, mussels and scallops
         Class Cephalopoda:
 Nautilus, cuttlefish, squid, octopus
      Class Monoplacophora
 Limpet-like shell
 Chiton-like segmentation
 Mostly deep sea
        Class Aplacophora
 No shell, worm-like

          Photo: Woods Hole Oceanographic Institute
          Class Scaphopoda
 Tusk shells

        Classic protostomes
 Hypothesis 1:
Based on molecular data, cuticle features
        Bauplan basics
Sketch along with the professor!
 Shell
 Mantle
 Mantle cavity, contains
     Ctenidia
     Anus & Renal/genital pores
 Foot: wide, flat and muscular
     Note epipodial tentacles in some
 Head
     cephalic tentacles
     radula
 Visceral mass enclosed by mantle
     Contains main body systems
   Radula or filter feeding
     Structure used for filter-feeding in
   Salivary glands with toxins, digestive
   Complete digestive system
   Anus empties into mantle cavity
          Circulation/gas exchange
   Ctenidium (sketch)
     Ctenidial axis & ctenidial filaments
     Hemolymph flow, water flow &
      countercurrent exchange
   Circulatory system
     Open (except Cephalopoda)
     Heart with two atria and a muscular
     Pericardial cavity is part of reduced coelom
         Note key aspects of circulation pattern! [Fig.
Circulation/gas exchange
 Metanephridia (=kidneys)
  Also associated with reduced coelom
  Nephridiopore (renal pore) empties into?
                Nervous system
   “Primitive” forms: i.e. Polyplacophora
     Ganglia at head
     Four longitudinal cords
     Cross-connections
                 Nervous system
   Gastropoda
     Ganglia at head
     Two longitudinal cords
     Additional ganglia

           Pre-torsion            Post-torsion
   Gonochoristic or hermaphroditic
   Gonads associated with reduced
     Ancestral condition: spawning via genital
      pores (empty into mantle cavity)
         Sometimes linked with nephridiopore
     Some with elaborate structures &
      behaviors for internal fertilization
          Focus: Cephalopoda
   Diversity: living forms (slides)
       Nautilus
       Cuttlefish
       Squid
       Octopus
   Evolution of cephalopods
 Ancestral cephalopod: key features
 Three key lineages (handout)
  Nautiloids and Nautilus features (handout)
 See handouts for key features
Extinct Coleoidea: Belemnoidea
      Focus: extant Coleoidea
       Predatory adaptations
 Previously…
  Streamlined shape
  Shell reduction
  Funnel/siphon  jet propulsion
 Further arm development
 Further cephalic tentacle development
 Eye development
           Eye structure
 Classic example of convergent evolution
      Focus: extant Coleoidea
       Predatory adaptations
 Nervous system
 Further adaptations of the mantle
  Chromatophores (slides)
 Ink sac
Life history: Loligo opalescens
   Mating
   Egg laying
   Development
   Hatching
   Where have all the young squid gone?

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