Mollusca

• Gastropoda - Shell, when present

  usually coiled.
• Cephalopodia - No shell
• Bivalvia - Two shells
• Gastropoda - Body symmetry distorted

  by torsion
• Gastropoda - Some monoecious species.
• Cephalopoda - Foot modified into a circle

  of tentacles and a siphon.
• Cephalopoda - Shell reduced or absent
• Cephalopoda - Head in line wit elongated

  visceral mass.
• Scaphopoda - Body enclosed in a tubular

  shell that is open at both

  ends.
• Scaphopoda - Tentacles used for deposit

  feeding
• Scaphopoda - no heads
• Polyplacophora - Elongated, dorsoventrally

  flattened.
• Polyplacophora - Shell consisting of eight

  dorsal plates
• Polyplacophora- head is reduced in size
• Monoplacophora - Molluscs with a single

  arched shell.
• Monoplacophora - Certain structures serially

  repeated
• Monoplacophora - Foot broad and flat
• Solenogastres - Shell, mantle and foot

  lacking.
• Solenogastres - worm like
• Solenogastres - Ventral (pedal) groove
• Solenogastres - Head poorly developed
• Solenogastres - Surface dwellers on coral

  and other substrate
• Caudofoveata - Worm-like molluscs with

  cylindrical, shell-less and

  scale-like, calcareous

  spicules.
• Caudofoveata - Lack eyes, tentacles,

  statocysts, crystalline style,

  foot and nephridia
• Bivalvia - Clams, oysters, mussels,

  scallops

  ❑ 30,000 species
• Bivalvia - Shell and associated

  structures

  ✓ Single shell consisting of

  two hinged valves.

  ✓ Mantle sheet-like and

  covers laterally

  compressed body.
• Reproduction

  ❑ Generally dioecious, but some animals are hermaphrodite.

  ❑ Fertilization external or internal.

  ❑ Development may director through free larval forms like

  glochidium; trochophore or veliger larva.
• RESPIRATION

  ❑Aquatic species have gills enclosed within the mantle cavity

  ❑Terrestrial snails and slugs have a modified lung
• PROTECTION AND SUPPORT

  ❑Hemocoel(s)

  ✓ Can function as hydrostatic

  skeleton

  ✓ Can be filled with water or gas

  and exert pressure that provides

  structure and support to the

  body

  ❑Shells

  ✓ Calcium carbonate with protein

  ✓ Secreted by the mantle

  ✓ Sometime internal (cuttlefish)
• EXCRETION

  ❑Nephridia remove

  metabolic wastes and

  regulate the balance

  of water and ions in

  the body.
• CIRCULATION:

  ❑Open (except in cephalopods)

  ❑Blood is released directly into

  organs and body cavities

  (hemocoel)

  ❑No clear distinction between blood

  and interstitial fluid – blood is

  known as hemolymph.

  ❑Hemolymph contains hemocyanin

  to transport oxygen; appears blue

  when exposed to air
• DIGESTION:

  ❑ Complete – mouth & anus with special organs

  Radula: Many mollusks possess

  a specialized feeding structure

  ❑ A rasping, tongue-like organ

  covered in rows of small

  teeth.

  ❑ The radula is used for

  scraping, tearing, or drilling

  food, depending on the

  species' diet.
• BODY REGION: MUSCULAR FOOT

  ❑ Base of the mollusk body

  ❑ Contains statocysts

  ✓ Sensory cells that assist with

  balance

  ✓ May function as “ears” for some

  ❑ Adapted in various ways

  ✓ Locomotion in gastropods

  ✓ Tentacles in cephalopods

  ✓ Burrowing in bivalves
• What types of mollusca in the picture

  Monoplacophora

  
• what mollusca is this?

  Bivalvia

  
• What mollusca is this?

  Caudofoveata

  
• What mollusca is this?

  solenogastres

  
• What mollusca is this?

  Polyplacophora

  
• What mollusca is this?

  Gastropoda

  
• What mollusca is this?

  cephalapoda