Phylum Mollusca Soft – bodied invertebrates Clams, Octopus, Snails
Jan 18, 2016
Phylum Mollusca
Soft – bodied invertebratesClams, Octopus, Snails
Characteristics
• Coelomates• Trochophore larva (aquatic molluscs)• Divided into head – foot and visceral mass– Visceral mass contains the hear and organs for
digestion, excretion, and reproduction• Coleom surrounds the heart
• Mantle, epidermal tissue secretes the shell– Calcium carbonate
• Gills– Found within the mantle cavity
• Most are bilaterally symmetrical• Nervous system – Pair of ganglia in head – foot and visceral mass
• Radula
Phylum Mollusca Divided into 7 classes
• Focusing on 3 classes– Gastropoda, one or no shell (snails)– Bivalvia, two shells with hinge (clams)– Cephalopoda, tentacles (octopus)
Snapshot of Mollusca Diversity
Class Gastropoda
• Largest and most diverse group• Single shell• Torsion– Larval development visceral mass twists 180
degrees in relation to the head– Brings anus, gills, and mantle cavity in the front– Allows adult to pull itself into the cavity when
threatened
• Moves by using wave – like motion of foot• Open circulatory system– Hemolymph • Flows into hemocoel (blood cavity)
• Separate Sexes but may be hermaphroditic
Class Bivalvia• Shell is divided into 2 halves (valves) and
connected by a hinge• Close the shell by contracting is adductor
muscles, open by relaxing them• Three layers secreted by mantle– 2nd layer consists of calcium carbonate
Bivalvia• Sessile (foot)• Filter – feeders• Nervous system– 3 pr of ganglia (mouth, digestive system, foot)
Clams
• Bury in mud– Siphons extend past shell– Cillia on the gills pull water in the incurrent sipon– Water/food particles pass over the mucus on the
gills and food becomes trapped• Oxygen is absorbed
– Water exits the clam through the excurrent siphon
Clam Anatomy
• Separate sexes – Gametes are released into water– Trochophore larvae
• Freshwater clams
Class Cephalopoda
• Head – foot• Specialized for free – swimming predatory life• Circle of tentacles from the head• Beak• Advanced nervous system– Lobes with nerve cells– Sensory system
• Closed circulatory system– Rapid movement of materials
• Separate sexes• Egg into juvenile without trochophore larva• Chromatophores
Squid/Cuttlefish
• 10 tentacles• Internal shell
Octopuses• 8 tentacles
Chambered Nautiluses
• Retains external shell– Coiled and divided into series of gas – filled
chambers– Soft – body moves forward as the organism grows– Buoyant