Transcript Mollusks
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 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 Mollusks Trochophore Larval stage of mollusks and annelids Developed from fertilized egg Free-swimming Cilia used for movement Three Major Classes of Mollusks 1. 2. 3. Gastropoda – snails, slugs Bivalvia – clams, oysters and scallops Cephalopoda – squid and octopus Characteristics of Mollusks Body Cavity – true coelom Symmetry - bilateral Three-part body plan 1 2 3 Visceral mass – organs Mantle – outer layer of body wraps around visceral mass Foot – 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 – • a. 8 muscular tentacles • b. No shell • c. Use suction cups for • movement • d. can squeeze into tight • spaces • e. most are small in size 2. Squid – a. 10 tentacles ( 2 long, 8 short) b. use fins and jet propulsion for moving c. range in size from small to giant in size 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 33.16 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 c. Chromatophores for camouflage d. fins e. Well developed eyes f. greenish-blue blood Figure 33.19 Gastropods: Nudibranchs (top left and bottom left), terrestrial snail (bottom left), deer cowrie (bottom right)