Phylum Mollusca Soft-bodied animals!

3 Classes of Molluscs GASTROPODA : includes limpets, snails, slugs and whelks BIVALVIA: includes clams, oysters, mussels, scallops and shipworms CEPHALOPODA: includes octopi, squid, cuttlefish, and nautilus Above: Scallop showing off its eyes! Left: Cuttlefish and squid Above: Limpet

All forms of Molluscs have a body with three parts: 1. Visceral Mass - The soft bodied portion that contains the internal organs 2. Foot - A strong, muscular portion used for moving (or tentacles in cephalopods) 3. Mantle -A covering that goes around the visceral mass -Can secrete a shell

Find the Foot, Visceral Mass and Mantle!

A diverse phylum ► Mollusca contains 80,000 different species ► Symmetry: Bilateral ► Level of Organization: Organ ► They also have a well developed nervous system, a circulatory system, and a brain.  Cephalopods have a closed circulatory system (e.g. squid, octopus…)  Bivalves and Gastropods have an open circulatory system (e.g. clams, snails…)

► Feeding:  Complete digestive tract  Most have a radula – a sharp “tongue” like a nail file that they use to rasp at food  Feeding strategies differ between the classes ► Excretion:  Complete excretory system with an anus  Simple kidneys ► Reproduction:  Sexual with internal fertilization  Most have separate sexes, although snails are usually hermaphroditic

Class Bivalvia ► Two valves (shells), e.g. mussels, clams, oysters ► They have a muscular foot for digging ► They often attach to the substrate with byssal threads that hold them in place ► Some, like scallops, can swim

► Siphons (tubes to carry water into and out of the animal) ► A muscle holds the valves (shells) together ► No head, radula or true eyes (eyespots only) ► Gills for getting oxygen from the water ► Open circulatory system

Above left: Elephant trunk clams, named for their large foot Above right: an opened oyster commonly enjoyed raw or cooked as a delicacy Lower right: Scallop showing off its many primitive eyes

Giant clams have zooxanthellae, just like corals

Class Gastropoda ► Gastropod means stomach-foot ► They usually have one shell, e.g. snails ► They have a variety of feeding methods – some are herbivores, some carnivores, some parasites ► Some cone snails inject a venom that can be fatal to humans

► Snails have a hard “door” called an operculum ► Internal fertilization and are often hermaphrodites ► Use a radula for feeding

Gastropod Diversity

Also in Class Gastropoda… The Nudibranch! ► Nudibranch means “naked gills” ► They have evolved to have no shell

► Toxic and have bright beautiful colors as a warning to predators ► The feathery parts on their backs are their gills ► Two rhinophores that “taste” the water around them to sense their environment

Top 5 reasons why Nudibranchs are so cool… ► 5. They are amazing colours… ► 4. They can eat toxic sponges without being harmed, but can transfer the toxin to a predator if bitten ► 3. Hermaphroditic nudibranchs battle to be the one to inject the other with sperm.

► 2. They can eat nematocysts from corals and anemones without getting stung. The next thing that touches them gets the sting! ► 1. A nudibranch can eat algae and take the chloroplasts into its own body. It can then perform PHOTOSYNTHESIS!

Class Cephalopoda ► Their name means “head – foot” ► E.g. Octopus, squid, cuttlefish

► They have 8 (or more) arms ► They can push a jet of water out their siphon, allowing them to move quickly ► An ink sac allows them to eject ink as decoy

► The Nautilus has a shell with chambers that allows it to change depth easily (they are great hunters)

► Many cephalopods have no shell  Squid and cuttlefish have a hard part inside  Octopus have no hard parts except for their mouth

► Cephalopods have a very well developed nervous system ► nerves can carry messages TEN times faster than in humans ► Their eye is complex and has 180 degree vision out of the sides of their heads

head liver stomach heart tentacles suction cupskidney eye beak siphon inksac

► They have a developed brain and can solve problems ► Mouth is called a beak ► They have internal fertilization and have separate sexes  male has a special tentacle used to put sperm packets inside the female  Squid mate in a big group

 Female octopus lay thousands of eggs in a cave and guards them until she dies

Octopus Octopus beak Octopus on the beach Swimming OctopusOctopus arm in detail

► Many have photophores that allow them to produce light ► Most also have chromatophores that allow them to change color to match their background

Squid Caribbean Reef SquidTentacles of a giant squid Calamari: a deep fried squid dishSquid eye and gills

Squid Fact Squid Fact The largest squid ever caught was a 10 m long Colossal Squid off the coast of New Zealand and weighed in at 495 kg. Colossal Squid are larger than the giant squid found off the Mexican coast and are thought to grow in size to 13 meters!