Polyplacophora Gastropoda Bivalvia Scaphopoda Cephalopoda Phylum Mollusca Polyplacophora Gastropoda Bivalvia Scaphopoda Cephalopoda Phylum Mollusca

Molluscs One of the largest of all phyla Have adapted to a wide variety of habitats Terrestrial, marine, benthic, and accomplished swimmers. Phylum Mollusca

The Molluscan Body Plan Despite the external differences between snails, clams, and squids the body plan is similar and distinct from all other phyla The Mollusca body plan includes: A large muscular foot A radula Mantle and mantle cavity Usually a small head Soft unsegmented body A hard non-living calcareous shell Phylum Mollusca

The Foot Phylum Mollusca

The Radula Radula Phylum Mollusca

The Mantle The mantle is the body wall that enclose the body cavity Phylum Mollusca

The Mantle Cavity Houses the visceral mass and comb-like gills Gills are respiratory in function and can collect food particles Mantle cavity also is the site for reproductive, excretory, and digestive systems The molluscan coelom is very small; being restricted to the area surrounding the heart and gonads Phylum Mollusca

Taxonomic Summary Phylum Mollusca Class Polyplacophora Class Gastropoda Class Bivalvia Class Scaphopoda Class Cephalopoda Phylum Mollusca

Systems Skeletal- Mantle may secretes a shell. Use hydrostatic pressure for ventral muscular foot. Muscles -Ventral muscular foot and other muscles present. Digestive- complete complex with salivary glands, digestive gland and Rasping tongue (Radula).

Systems Circulatory - Open except for Cephalopoda. Dorsal heart, usually in a pericardial cavity. Respiratory - Ctenidia (gills) in mantle cavity, respiratory pigment is copper. Phylum Mollusca

Systems Excretory- by nephridia usually connecting to the pericardial cavity, the coelom is usually reduced to the cavities of the nephridia, gonads and pericardium. Nervous - Nerve ring with various pairs of ganglia—two pairs of nerve cords, one innervating the foot, the other the visceral mass (modified ventral ladder-like system)

Systems Integumentary – Mantle Endocrine - nervous systems produces hormones. Reproductive - varied- monoecious, protandric, or dioecious. Larva in marine = trochophore and veliger, in freshwater clam is glochidium. Phylum Mollusca

Phylum Mollusca Class Polyplacophora Phylum Mollusca

Class Polyplacophora Chitons Phylum Mollusca

Chiton Lifestyles Found close to shore mainly in the intertidal where they live on hard substrates Strong foot and low profile help from being swept away Phylum Mollusca

Ingestion and Digestion Radula is used to scrape algae from the rocks Mouth is anterior and anus is posterior; linear digestive tract Phylum Mollusca

Phylum Mollusca Class Gastropoda Phylum Mollusca

Class Gastropoda Defining characteristics Visceral mass and nervous system become twisted 90-180° during embryonic development Largest and most varied group of the phylum Mollusca Phylum Mollusca

Gastropod Morphology and Movement The typical snail consists of a visceral mass, which sits atop a muscular foot The visceral mass is protected by a univalve shell that is coiled Phylum Mollusca

Phylum Mollusca

Prosobranchia Anatomy Molluscan gill Consists of a series of flattened, triangular sheets Water is drawn into the animal by gill cilia Phylum Mollusca

Phylum Mollusca Class Bivalvia Phylum Mollusca

Class Bivalvia Defining characteristics Two-valved shell Body flattened laterally This class contains clams, oysters, mussels, scallops, and shipworms Phylum Mollusca

Bivalves and You Many species are edible In today’s waters this can cause certain problems since bivalves are filter feeders Also, an important food item for our commercially important fish Important to humans in their ability to strain harmful bacteria out of polluted waters Some can pump up to 40 liters per hour Phylum Mollusca

Bivalve Locomotion? Most bivalves move by expansions and contractions of the foot Mussels usually are sessile and attach to substrate with threads Phylum Mollusca

Phylum Mollusca

Bivalve shells Protein hinge ligament stores energy required to open the shell Adductor muscles is responsible for closing the valves The umbo is dorsal and the valves are addressed as left and right Siphons are posterior and the excurrent siphons are always dorsal Phylum Mollusca

Phylum Mollusca

The Mantle Phylum Mollusca

Bivalve Feeding Bivalves are filter feeders Ctenidia, gills, are used for feeding & respiration and are enlarged and folded to increase surface area Cilia on the gills create a current to bring food-laden water into the mantle cavity Phylum Mollusca

Bivalve Reproduction Dioecious The male sheds sperm into the water column Sperm can enter the female or fertilization can occur in the water column Phylum Mollusca

Class Scaphopoda Class Cephalopoda Phylum Mollusca Class Scaphopoda Class Cephalopoda Phylum Mollusca

Class Scaphopoda Defining characteristics Tusk shaped conical shells, open at both ends Development of anterior thread-like adhesive feeding tentacles Elongated tapering tubular shells that burrow in sandy bottoms Phylum Mollusca

Phylum Mollusca Class Cephalopoda Phylum Mollusca

Class Cephalopoda Defining characteristics Closed circulatory system Foot modified to form flexible arms and siphons Ganglia fused to form a large brain encased in a cartilaginous cranium Phylum Mollusca

Cephalopod Characteristics The most highly organized of all the molluscs, the foot is closely associated with the head Nautilus, octopus, cuttlefish, and squids Shell size varies from a full shell (nautilus) to a vestige of a shell in the squid and octopus Can be as large as 1,000kg. and 18m. Phylum Mollusca

Squids Octopuses Chambered Nautiluses 10 tentacles. Propels by pumping jets of water with the mantle through an excurrent siphon. Octopuses 8 tentacles They often crawl along the ocean bottom or lie in wait for prey. Chambered Nautiluses The only existing cephalopod with external shell. Shell is coiled & divided into chambers. The body is confined to the outermost chamber.

Defensive Mechanisms Since they are susceptible to predation they have evolved chromatophores May posses hundreds or thousands, all controlled by the brain An ink sac that is associated with the digestive system and discharged out the anus Phylum Mollusca

Sensory & Nervous System Eyes All but the nautilus have image forming eyes that are like mammals Convergent evolution Phylum Mollusca

Reproduction Sexes are separate Males have one modified arm (hectocotylus) for sperm transfer Sperm are enclosed in packets called spermatophores Phylum Mollusca

Squid 10 sucker bearing arms surround the mouth 2 longer tentacular arms can shoot forward and capture prey Large bites of food are removed and swallowed quickly Form large schools and feed on crustaceans, and fishes The shell is reduced and lies under the mantle, pen Large folded gills and a circulatory system distribute oxygen quickly High oxygen demands are meet by the contraction of the mantle cavity This method also removes waste products Phylum Mollusca

Squid Internal Anatomy Phylum Mollusca

Squid Locomotion The foot forms the funnel The upper end of the mantle is extended into a pair of triangular fins Water enters the mantle cavity at the free end When the mantle contracts the edge is tightly sealed and water is forced out the funnel Can move very quickly 5-10 m/s Phylum Mollusca

Octopods Have 8 arms all equal in length Rows of suckers from base to tip Compact body with a greatly reduced shell The body is extremely flexible and assumes a streamlined shape when swimming with squid-like jets through the funnel Phylum Mollusca

Learning and Memory Benthic feeders on bivalves, crabs and fishes Some are pelagic and spend their entire life swimming, usually at great depths Amazing ability to learn quickly and remember for several weeks Phylum Mollusca