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 – 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 – 2 nd 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