Mollusca - soft-bodied 

• level of organization - organ systems
• body symmetry - bilateral symmetry
• alimentary structures - 2-hole tube
• triploblastic
• coelomate - contains fluid-filled space surrounded by mesoderm layer to hold organ systems
  • coelom isolated to area around heart in mollusks
  • not the same as digestive/mantle cavities
• mantle - specialized epidermal cells, can secrete shell
• visceral mass - organ systems, sensory structures
• open circulatory systems in all except Cephalopods
• gas exchange occurs in gills
• Class Polyplacophora - “many moving plates”
  • uses radula (horny tongue) to scrape food from rocks
  • dorsal shell divided into 8 plates
• Class Gastropoda - “stomach foot”
  • single, coiled shell produced in snails
  • no shells for slugs/nudibranchs
  • uses radula
• Class Bivalvia - “two doors/valves”
  • hinged shell for protection
  • sessile filter feeders
  • incurrent/excurrent siphon directs water through clam
• Class Cephalopoda - “head-foot”
  • shell internalized or lost
  • can alter shape/color for camouflage
  • hardened beak for crushing prey
  • tentacles w/ suckers to ensnare prey
  • most intelligent/advanced of invertebrates

Annelida - “ringed/segmented”

• level of organization - organ systems
• body symmetry - bilateral symmetry
• alimentary structures - 2-hole tube
• triploblastic, coelomate
• segmentation - divided into parts separated by septa
  • muscles can elongate/contract for locomotion
  • parts specialized for certain tasks
• closed circulatory system
• setae - small bristle-like appendages
• no gills/lungs, oxygen absorbed through moist body surfaces (cutaneous respiration)
• mouth >> pharynx >> esophagus >> crop >> gizzard >> intestine
• can only reproduce through cross-fertilization, even though it’s hermaphroditic
  • sperm exchanged through clitellum
• Class Polychaeta - “many setae”
  • well defined heads
  • can be venomous
  • active predator/scavenger
• Class Oligochaeta - “few/small setae”
  • earthworms, redworms, etc
• Class Hirudinea - leeches
  • secretes hirudin as anticoagulant
  • some live as ectoparasites