Mollusca

• What makes a mollusc -

  mantle

  foot

  radula

  shell
• name means soft bodied
• estimated 200,000 species (most diverse phylum of marine invertebrates)
• 25% of all named marine organisms are molluscs
• the ONLY phylum with species found in the sea, freshwater and on land
• fossile record is exceptional, especially with clams (bilavia) and snails (Gastropoda)
• Puntum Minutimissimum is the dot snail
• Meifauna is between 1mm and 45 micro metres
• some molluscs live in the meiofauna for some/all their lives
• colossal squid - mesonychoteuthis Hamiltoni

  the largest known invertebrate (14m+)
• Giant squid - Architeuthis dux

  10m+
• the body plan is highly adaptable so molluscs can adjust their morphology to almost any habitat type on the planet
• the mantle, shell, radula, and foot are particularly adaptable features
• Features shared by all molluscs

  unsegmented, soft body with bilateral symmetry
• Mantle -> sheet of tissue covering the body (like skin), the mantle produces the shell (features shared by all molluscs)
• external or internal share (features shared by all molluscs)
• muscular foot and/or tentacles (features shared by all molluscs)
• radula - a tongue like structure with small teeth for scraping food particles off a surface and drawing them into the mouth (features shared by all molluscs)
• Bolivia do not have a radula because they are filter feeders
• The mantle - skin like organ that covers much of the dorsal (i.e the back) portion of molluscs
• The mantle - all molluscs have a mantle (covers the visceral mass (the body cavity that contains organs/gonads/digestive system etc.)
• The mantle - often protrudes from the body of the organism, sometimes resembling a cloak
• The mantle - the outer layer of the mantle secretes CaCO3, forming the molluscan shell
• The shell - all mollusc classes, except the aplacophorans have solid calcareous shell (made of either aragonite or calcite)
• The shell - the shell is produced by the mantel epidermis (outer layer) from shell glands
• The shell - molluscan shells vary greatly in shape, size, and colour.
• The shell - molluscs can have:

  no shell (aplacophora)

  1 shell (i.e Gastropoda, monoplacophora, Scaphopoda, Cephalopoda)

  2 shells (bivalves)

  8 shells (polyplacophora)
• The shell - shell shape and structure is a reflection of the behaviour evolution and habitat of the organism
• The radula - little scraper
• The radula - used for grazing or as a tool for durophagy (drilling into shells)
• The radula 'teeth' of limpets are the hardest known biologically made substance
• the radula - cone seals (conus) use modified radula tooth as a dart/harpoon to capture their prey
• The radula - the barbed radula tooth carries toxic venom
• The radula - radula tooth is extended from its proboscis into its prey (fish or small inverts)
• The radula - highly toxic venom (some species can kill a human)
• The radula - >800 species described worldwide
• The radula - primarily live in warm tropical waters
• The foot - a muscular organ that is used for locomotion in molluscs
• The foot - molluscs modify their morphology of their foot as adaptations to the their environment
• The foot - molluscs use their foot to

  -burrow into the sediment (e.g bivalve, Scaphopoda)

  -move along a rock or soft sediment surface (e.g Gastropoda)

  -for swimming (e.g preropods)

  -modified as tentacles to capture prey and manipulate objects (e.g Cephalopoda)