Soft – bodied invertebrates Clams, Octopus, Snails Phylum Mollusca Soft – bodied invertebrates Clams, Octopus, Snails

Characteristics Coelomates Trochophore larva (aquatic molluscs) Divided into head – foot and visceral mass Visceral mass contains the heart and organs for digestion, excretion, and reproduction Coleom surrounds the heart

Mantle, epidermal tissue secretes the shell Gills 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 Freshwater clams 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 Separate sexes 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