Mollusks

• Mollusk Basics

• invertebrate
• soft, unsegmented body
• aquatic, damp environments
• most have external, calcareous shell

• calcareous = contains calcium carbonate, chalky

• 3 Classes of Mollusk

• Bivalve
• Gastropod
• Cephalopod

• Bivalves

• BI (Two) - Valve (shell)
• Shells hinged together at one end and are kept closed by a short, tough ADDUCTOR MUSCLE.
• Examples: Mussels, Clams, Oysters

• How does a bivalve build its shell?

• Within the mantle are SHELL GLANDS that secrete CALCIUM CARBONATE to produce the shell
• Rings can be used to calculate age

• How does a bivalve eat?

• Filter Feeders- filter their food from the water
• Siphon Tube
• Incurrent siphon – WATER THAT CONTAINS FOOD AND OXYGEN ENTER HERE
• Excurrent siphon – WASTE PRODUCTS OF DIGESTION AND RESPIRATION ARE ELIMINATED HERE

• Adaptations of bivalves to help with feeding

• Tough BYSSAL THREADS with sticky pads that allow them to bind to hard surfaces. (EX. MUSSELS)
• Oysters can secrete a CEMENT to help them bind to surfaces.

• How do oysters make pearls?

• A pearl begins to develop when a SAND GRAIN gets into an oyster and lodges between the mantle and the shell.
• The mantle tissue reacts to the sand grain as a FOREIGN BODY and secretes layers of shell around the grain forming a PEARL.

• Movement of bivalves

• Fastest moving bivalve is the SCALLOP
• also have about 60 blue eyes for sensing
• Move across the seafloor in sudden spurts by opening and closing quickly.

• Other Bivalves move through substrates (EX. Sand and MUD)

• Bivalves such as RAZOR CLAMS and SOFT-SHELLED CLAMS use their muscular foot to dig.

• Reproduction of bivalves

• Bivalves have separate sexes:
• FEMALES: release their eggs into the water.
• MALES: release their sperm to fertilize eggs.
• In the early stages of development, the bivalves exist as part of the PLANKTON community. Eventually, they develop their shells, sink to the bottom and mature into adults.

• Gastropods

• UNIVALVES: “ONE SHELL”
• Account for 2/3 of all mollusks
• Examples: Snails, conch, abalone, whelks

• Tentacles

• Gastropods have 2 sets of tentacles
• Upper (posterior): eye stalks

• used to respond to light

• Lower (anterior): sensory tentacle

• used for smelling and tasting
• help find food and avoid dangerous areas

• Redula

• tooth-like structures that scrapes off and ingest algae from surfaces

• Other Gastropods

• Sea Slugs and Nudibranchs

• Cephalopods

• Examples: Squid and Octopus
• Refers to the class of swimming mollusks that use JET PROPULSION for motion (through the siphon)
• Streamlined body shape
• Lack an external shell (soft-bodied)
• Invertebrates
• Over 800 living species

• Squid body plan

• Octopus body plan

• Cephalopod body parts

• Mantle

• main body of the squid
• protects organs
• made of muscle and skin

• Beak

• In addition to radula (tiny teeth), cephalopods have a large beak made of chiton surrounding its mouth.  
• Used to chop and slice up prey before the food is passed.

• Shell

• Octopuses do not have shells. Over millions of year, the shell has been reduced to nothing.  
• Squid, on the other hand, have an internal structure called a pen or gladius. This structure is made of cartilage and supports the mantle.

• Siphon

• Siphon (Funnel)
• muscular structure
• respiration, discharge of waste, propulsion

• Arms vs. Tentacles

• Arms: all arms are equal in length with suction cups lining their entirety
• Tentacles: longer than the arms and have suction cups only at the ends

Creature	Arms	Tentacles	Suction cup purpose
Squid	8	2	grasping prey
Octopus	8	0	climbing

• Eyes

• Cephalopods have eyes that are so well developed that they can see as well as people do.

• Chromatophores

• Allow for some species to change color to better help them to camouflage

• give skin its reddish-pink color
• when these cells contract, the skin appears paler
• under stress, may appear red
• to hide from predators
• to catch prey

• Intelligence
• Ink

• Most cephalopods are able to release ink as an escape mechanism.
• The ink is released from the ink sacs in the body and shot out of with a jet of water from the siphon.  

• octopuses: black ink        
• squid: blue-black ink        
• cuttlefish: brown ink

• Other types

• Giant squid
• Cuttlefish
• Chambered nautilus