Presentation on theme: "Cephalopods, Gastropods, Bivalves and their Relatives"— Presentation transcript:
1Cephalopods, Gastropods, Bivalves and their Relatives Phylum MolluscaCephalopods, Gastropods, Bivalvesand their Relatives
2Characteristics of the Group Most numerous phylum in the ocean by # of species (200,000)Soft bodied with a calcium carbonate shellBilaterally symmetrical but not alwaysGas exchange through paired gillsUbiquitous in marine environmentsUnsegmentedHave a head, foot, and body in some arrangement
3Unique StructuresMantle – thin layer of tissue that secretes the shell.Foot – ventral, muscular organ that is used in locomotion (sometimes modified into tentacles)Radula – ribbon of small teeth made of chitin that are used in feeding
4Mollusc Body Plan Gonad Intestine Shell Radula Stomach Heart Digestive GlandMantleGillFootNervous System
5Gastropods Means “stomach footed” Most numerous and varied group of molluscsInclude snails, limpets, abalones, and nudibranchs
6Characteristics of Gastropods “Coiled mass of vital organs surrounded by a dorsal shell”Have a ventral footWith their radula they inhabit most all feeding niches – carnivores, detritivores, herbivoresShells can be very elaborate, may be internal, or could be missing entirely.
9Nudibranchs Sea slugs Name means “naked gill” Have lost the shell entirelyUsually brightly coloredCan keep and incorporate noxious chemicals and undischarged nematocysts from prey for defense.
10Bivalves Have a two valved hinged shell. Body is laterally compressed. No head or radulaGills are used to obtain oxygen and filter foodMantle surrounds body.Strong muscles are used to close the valves of the shell
11Clams Burrow in sand and mud Use siphons to move water in and out –permits eating and respiring while buried.Some contain iridescent chemicals in their tissues
12Mussels & OystersInstead of burrowing, they secrete byssal threads that attach them to rocks and other surfaces.Oysters cement themselves to the substrate.Some bivalves like shipworms bore into wood. The wood is digested by bacteria in the gut of the organism.Oysters attach to substrate by their left shell.Pearl oysters –thin layer of calcium carbonate coat irritating particles or parasites lodged between the mantle and the inner shell (mother of pearl).Ginat clams – 1 mCommon source of food
14Cephalopods Means “head-footed” About 650 species Body such that head is between “feet” and body.Includes octopuses, squid, cuttlefishes, and the chambered NautilusGiant Pacific Octopus
15Cephalopod Characteristics Agile swimmersComplex nervous systemShell is reduced or lost entirelyFoot is modified into tentacles usually equipped with suckersEyes are well developedMove by forcing water out of the siphon, a flexible, funnel-shaped tube on the side of the head.
16Octopuses Eight arms and no shell Bottom dwellers 5cm – 9m Predators on crabs, lobster, shrimp, small fish, and other molluscsHave a hard “beak”Some like the blue-ring secrete a highly toxic venom in their biteCan emit a dark ink to confuse attackersFrom Greekoktopous meaning “eight-footed”Blue ringed octopus
17Squid Elongate body Mantle contains two triangular fins. Eights arms + two retractable tentaclesShell reduced to a chitinous pen inside the mantleFew cm to 12 m
18CuttlefishesResemble squid but with a flattened body and a rippling fin surrounding the mantle.Have a calcified internal shell or “cuttlebone.”
20The Chambered Nautilus Have a smooth coiled shell up to 25 cm in diameter.Chambers in the shell are filled with gas to provide buoyancyHas short, suckerless tentacles for capturing fishLiving fossilFrom Greek nautilos meaning sailor because it was once thought to use its shell like a sail.
22Molluscan Digestion Separate mouth and anus Have salivary and digestive glandsUse their radula to scrape, drill, cut, or capture prey.Digestion is extracellular and intracellular.Bivalves have a crystalline style in their gut that secretes enzymes.Some can even retain ingested chloroplasts that continue to photosynthesize and produce food for the mollusc
23Mollusc Circulation Open circulatory system Muscular heart pumps blood to all tissues.Cephalopods – closed circulatory systemBlood contained in vesselsMore efficient – meets the demands of large organs such as the brain.
24Mollusc Nervous System Gastropods and bivalves have ganglia.Cephalopods have a large fused brain that is divided into regions that control particular functions and behaviors.Octopus and cuttlefish can learn.Sophisticated color changes are believed to be coordinated by the nervous system.
25Mollusc ReproductionSome have external fertilization (tusk shells, bivalves, chitons, & some gastropods)Others have internal fertilization - a spermatophore, or sperm packet is deposited into the female via a modified arm (cephalopods) or a penis (gastropods).Most have separate sexes, but some are hermaphrodites
26Mollusc Reproduction continued… Some create a trocophore larvae which develops into a veliger (a planktonic larva with a tiny shell)Cephalopods lay eggs and the young develop from the yolk. Female octopus usually die after laying and guarding eggs – most likely due to starvation.