BIO190: The Class: Molluscs: Lesson 17

The Molluscs

The Mollusca is one of the largest animal phyla, there are nearly 50,000 living species and some 35,000 fossil species. The name Mollusca indicates one of their distinctive characteristics, a soft body.

There are eights classes in this phylum.
For additional information browse this site:
The Molluscs

The following are general characteristics of the mollusca.

1. "soft"
2. trochophore larva (fig. 17-6)
   1. possible link between annelids and molluscs

3. all organ sys. present
   1. respiratory
      1. gills/lungs/cutaneous

   2. circulatory
      1. open (except cephalopds)

   3. mantle (pallium)
      1. made from outgrowths of dorsal body wall
      2. houses gills or lungs
      3. encloses mantle cavity
      4. may secrete shell over visceral mass
      5. other functions through modifications

   4. radula
   5. muscular foot
      1. locomotion
      2. other functions as modified

   6. developed eyes in some
   7. bilateral sym.
   8. presence of calcium shell in most
   9. metanephridia
   10. nervous sys.
       1. various paired ganglia
       2. sensory organs
          1. touch
          2. smell
          3. equilibrium
          4. vision in some

       3. reproduction
          1. monoecious
          2. dioecious

       4. body plan (2 parts)
          1. head-foot
             1. feeding (fig 17-3)
                1. radula
                2. odontophore

             2. sensory (cephalic)

          2. foot
          
          locomotion
          1. gliding
          2. siphon
          3. attachment
          4. burrowing

       5. visceral mass contains
          1. digestive
          2. circulatory
          3. respiratory
          4. reproductive

       6. shell (fig. 17-5)
          1. 3 layers
             1. periostracum
             2. prismatic layer
             3. nacreous layer

          2. pearl formation
             1. "real vs cultured"

• Class Caudofoveata (pg. 327)

  Members of the Class Caudofoveata are wormlike, marine organisms.

• Class Solenogastres (pg. 327)

  The solenogastres are marine, wormlike, shell-less organisms.

• Class Monoplacophora (pg. 327)

• Class Polyplacophora (pg. 327-328)

  The chitons (fig. 17-9&17-10) represent a somewhat more diverse molluscan group.
  

  1. 8 plates on dorsal surface
  2. rocky shores/great depths
  3. feed on algae

• Class Scaphopoda (pg. 328)
  1. "tooth shells" (fig. 17-11)
  2. captacula

• Class Gastropoda (figs. 17-12 --> 17-23)

  Among the molluscs the Class Gastropoda is by far the largest and most diverse, containing about 40,000 living and 15,000 fossil species.

  1. univalves
  2. "stomach-foot"
  3. largest/most diverse
     1. marine/freshwater(FW)/terrestrial

  4. gastropoda anatomy
     1. apex
     2. whorl
        1. dextral
        2. sinistral

     3. aperture
     4. siphonal canal
     5. columella
     6. operculum

  5. torsion
     1. detorsion
     2. fouling

  6. coiling
     1. planospiral
     2. conispiral

  7. feeding habits
     1. herbivores
        1. radula

     2. scavengers
     3. carnivores
        1. borers
        2. directly
           1. modified radula to feed on fish, worm, other molluscs
           2. conotoxins

• Three groups of gastropods (based on respiratory physiology)
  1. Prosobranchia
  2. Opisthobranchia
  3. Pulmonata

• Class Bivalvia

  The Bivalvia are also known as Pelecypoda or "hatchet-footed" animals.

  1. "2 valves" = shells
  2. bivalve anatomy
     1. shell
        1. umbo
        2. concentric lines
        3. pallial line
        4. hinge ligament

     2. adductor muscles
     3. incurrent/excurrent siphons
        1. feeding
           filter feeders

     4. respiratory function
     5. food

  3. locomotion
     1. muscular foot
        1. boring types

     reproduction

     development

  4. Class Cephalopoda (figs. 17-36 --> 17-40)

     The Cephalopoda include the squids, octopi, nautilus, and cuttlefish. All are marine, and all are active predators.
     Open the following link for information on octopi:
     About Octopi

     1. "head-footed'
     2. modified foot
        1. siphon
           1. locomotion

     3. fossil record
     4. externally shelled vs unshelled (internally modified shells)

     5. communication

     6. nervous/sensory systems
        1. eye
        2. tactile
        3. ability to learn tasks

     7. ink gland
        1. sepia

     8. reproduction

     9. phylogency (pg. 345)

     10. adaptive radiation (pg. 345)

Once you have completed the lesson, you should go to Assignment 17-1.

E-mail Sylvester Allred at Syl.Allred@nau.edu

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