Gastropod Characteristics

Mollusks

• Second largest animal phylum with over 100,000 species
• Two unifying characteristics:
  • Calcium carbonate shell
  • Muscular foot for locomotion
• Some live in marine, fresh water, and terrestrial environments
• May weigh up to 900 kg and grow to nearly 20 m long, but 80% are under 10 cm in size
• Most mollusks are dioecious, some are hermaphroditic

General Characteristics

• Body plan consists of three main parts:
  • Muscular foot
  • Visceral mass (containing digestive, circulatory, respiratory, and reproductive organs)
  • Mantle
• Radula is a rasping, protrusible feeding structure found in most molluscs
• Calcareous shell is secreted by the mantle and is lined by it, consisting of three layers:
  • Periostracum (outer organic layer)
  • Prismatic layer (calcium carbonate)
  • Nacreous layer

Gastropods

• Mostly marine, but some live in fresh water and others are terrestrial
• Most gastropods have one shell, typically coiled or spiraled
• Numerous species have an operculum, a trapdoor to close the shell
• Feed using radula, can be herbivores, carnivores, or omnivores
• Respire through gills in marine species and lungs in terrestrial species
• Reproduce sexually, with some species exhibiting mating dances and using love darts

Bivalves

• Have a laterally compressed body enclosed by a shell in two hinged parts
• Most are filter feeders and have no head or radula
• Gills are specialized for feeding and breathing
• Most bivalves bury themselves in sediment to avoid predation
• Some bivalves can swim, such as scallops
• Sensory organs are not well developed, but some have simple eyes on the margin of the mantle

Cephalopods

• Modified foot is concentrated in head regions with sides of foot drawn out into arms and tentacles with suckers
• Habitat is marine, and they are carnivores
• Can change color using chromatophores
• Examples include squid, octopuses, and cuttlefish

Squid

• Have an internal shell
• Have eight arms and two tentacles to capture prey
• Strong swimmers, with some species able to fly short distances out of water
• Feed on small mollusks, crabs, shrimps, and fish
• Reproduce sexually with internal fertilization
• Have an ink sac that expels content to confuse predators

Octopuses

• Have two eyes and four pairs of arms
• Do not have internal or external skeleton
• Among the most intelligent marine invertebrates

Giant Squid

• Deep-ocean dwelling squid that can grow up to 13 meters in size and weigh up to 270 kg
• First photograph of this giant invertebrate was taken in 2004 in Japan