Mollusks

Mollusks  Include the following  Snails, slugs, oysters, clams, scallops, octopi, and squid  Second larges phylum in animal kingdom  More terrestrial mollusks than vertebrates

True Coelom  Mollusks and annelids – first group of organisms to develop a true coelom  Coelom – true body cavity with the gut as part of a suspended internal organ

Trochophore  Larval stage of mollusks and annelids  Developed from fertilized egg  Free-swimming  Cilia used for movement

Three Major Classes of Mollusks 1. Gastropoda – snails, slugs 2. Bivalvia – clams, oysters and scallops 3. Cephalopoda – squid and octopus

Characteristics of Mollusks  Body Cavity – true coelom  Symmetry - bilateral  Three-part body plan 1Visceral mass – organs 2Mantle – outer layer of body wraps around visceral mass 3Foot – muscular region used for locomotion  Organ systems – excretion, circulation, respiration, digestion and reproduction  Shell – exoskeleton protects soft body  Radula – rasping tongue-like organ in the mouth, used to scrape fragments of food off rocks or for attacking prey

Gastropods  Freshwater and terrestrial  Most have single shell  Foot used for locomotion  Forms slimy path  Herbivores that scrape algae off rocks

Snail - Gastropod

Gastropods: sea slugs and snails

Radula Muscular Foot

Bivalves  Most are marine, but some are fresh water  All bivalves have a two-part hinged shell  Adductor muscles - Two muscles connect the valves. When contracted they close the valves  Scallops open and close valves fast using the jet of water as locomotion  Filter feeders  Siphons – long hollow tube draws in water and filters it the excretes it through another tube

Scallop

Scallop

Oysters produce Pearls  A tiny grain of sand becomes lodged between the mollusk’s mantle and shell.  Oyster coats sand with nacre (mother of pearl) same material that makes the inside of the shell. It continues until the sand is completely covered.

Cephalopods  Squid and Octopus  Most of body is made up of a large head attached to tentacles (foot divided into many parts)  Squid have 10 tentacles  Octopus have 8 tentacles  No external shell  Squid have small internal shell

Class Cephalopoda – octopus, squid, cuttlefish, chambered nautilus“ head -footed” mollusks large heads and large eyes most intelligent invertebrates marine organisms active predators with strong beaks ability to change color ( camouflage) ink jets closed circulatory system tentacles with sucker disks

D. Examples of cephalopods 1. Octopus – 1. Octopus – a. 8 muscular tentacles a. 8 muscular tentacles b. No shell b. No shell c. Use suction cups for c. Use suction cups for movement movement d. can squeeze into tight d. can squeeze into tight spaces spaces e. most are small in size e. most are small in size 2. Squid – 2. Squid – a. 10 tentacles ( 2 long, 8 short) a. 10 tentacles ( 2 long, 8 short) b. use fins and jet propulsion for moving b. use fins and jet propulsion for moving c. range in size from small c. range in size from small to giant in size to giant in size d. small internal shell d. small internal shell

Blue-ringed Octopus

Squid  Most intelligent of all invertebrates  Complex nervous system with well developed brain  Complex behaviors (easily trained)  Some have color vision  Giant squid – largest of all invertebrates with largest eyes  Move quickly by shooting water out of siphon  Use ink to conceal the direction they move

Figure Basic body plan of mollusks Chambered nautilus – “oldest cephalopods” heavy external shell with chambers takes in and releases gas to move up and down in the water short tentacles

4. Cuttlefish a. Reduced internal shell b. 8 arms and 2 longer tentacles tentacles c. Chromatophores for camouflage camouflage d. fins e. Well developed eyes f. greenish-blue blood

Figure Gastropods: Nudibranchs (top left and bottom left), terrestrial snail (bottom left), deer cowrie (bottom right)