Lecture 9: Mollusks

• Types of marine worms:

  Sipunculids

  Nematodes (Roundworms)

  Priapulids
• Sipunculids are benthic burrowers that live in shallow waters and are suspension/deposit feeders
• Nematodes are the most abundant multi-cellular animals
• Nematodes are parasitic and free-living, have a complete gut, circulatory system, and nervous system, and have an organic casing known as the cuticle
• Priapulids are benthic, most live in cold waters, and are carnivorous, deposit feeders, and suspension feeders
• Types of marine SEGMENTED worms:

  Annelida

  Polychaetes

  Echiurans (Spoonworms)

  Pogonophora (Beardworms)
• Polychaetes exist as two groups: errant (active) and sedentary (sessile)
• Polychaetes can reproduce sexually via their reproductive form known as Epitoky:

  Posterior segments with either eggs or sperm
• Echiurians are infaunal, deposit feeders, live in shallow waters, and use a proboscis for locomotion, sensory, and gathering food
• Pogonophora live in tubes in deep water, have no mouth or digestive tract (derive nutrition from dissolved nutrients in seawater)
• Ecological roles of marine worms:

  1. Nutrient cycling: burrowing actions bring nutrients back to the surface and into the sea water
  2. Food chain: feed on material too small to be gathered by other marine organisms
  3. Habitat: burrows provide habitat for other species
• Phylum Mollusca is one of the largest and most successful groups
• Mollusca classes:

  Polyplacophora (Chitons)

  Scaphopoda (Tusk shells)

  Gastropoda (Limpets, snails, whelks, nudibranchs)

  Bivalvia (Clams, oysters, mussels, scallops)
• Gastropoda have the highest diversity, most have shells, and use their foot as an adhesive organ
• Bivalves have shells divided into 2 valves, have no head or radula, and feed primarily by filter feeding
• Bivalves have a catch muscle: muscles in bivalves that contract for extended periods without fatigue and with very little or no increase in oxygen consumption