Class Polyplacophora (Polys- many, Plaks- plate and phorus- to bear)
- " The Sea-Cradles"
- The Chitons
- All have 8 plates on their dorsum and ventral foot to adhere to the substrate, along with a reduced head and flattened foot
- Feed on attached algae
- Gills in the mantle cavity provide for respiration
- Cilia on the gills create water currents that enter below the anterior mantle margins and exit posteriorly
- The digestive, excretory, and reproductive tracts open near the exhalant area of the mantle cavity, and exhalant water carries products of these systems away
- Dioecious
- Nervous system is ladderlike, with 4 anterposterior nerve cords and numerous transverse nerves. Sensory structures like the osphradia which are tactile receptors on the mantle margin, chemoreceptors near the mouth, and statocysts in the foot
Class Scaphopoda (Skaphe- boat and Podos- foot)
- Tooth shells or tusk shells
- Over 300 species; all burrowing marine animals that inhabit moderate depths
- Tusk shells are burrowers and feed on foraminferals while lying on partially buried in the marine sediment
- Tubularorcome shaped shell is open at both ends
- Mantle is elongated and extends the length of the shell
- Various sensory structures are found in many places of the body
- Dioecious, Sexes are separate
- Have a trochophore and veliger larva in the life cycle
Class Monoplacophora (Monos- one, Plak- plate, and Phoros- to bear)
- Contains primitive molluscs with an extensive fossil record
- repeated pair of gills and foot retractor muscles
- Dioecious
- Neopilina is the only existing genus
Class Aplacophora (A- without, Plak- plate, Phoros- to bear)
- Divided into 2 subclasses of primitive shell molluscs
- Neomenimorpha (Solenogasters):
- Nervous system is ladderlike
- A small group containing a burrowing species that feed on microorganisms and dertritus, and possess a radula and nephridia
2. Chatetodermomorpha (Caudifiveata)
- Worm-like molluscs that range in size from 2mm- 14cm
- live in vertical burrows on the body wall
- scalelike spicules on the body wall
- lack: shell, crystalline style, statocysts, foot, and nephridia
- most burrow or creep on the substrate
- Have a nervous system similar to flatworms