Phylum Molluscs

Phylum Molluscs

Phylum Molluscshttps://www.youtube.com/watch?v=0a7j5prL8hc GeneralName means soft, or soft bodythis is one of the largest animal phyla, besides ArthropodaThere are nearly 75,000 species and some 35,000 fossil speciesVery diverse group (chitons, snails, clams, octopuses)Range from simple organisms to some of the most complex invertebratesSize from microscopic to huge (18 m giant squid)80% of molluscs are less than 5 cmMolluscs Classes Class Polyplacophora: ChitonsClass GastropodaClass Bivalvia (Pelecypoda)Class Cephalopoda

Hawaiian Bobtail Squid

Blue Ringed Octopus

Giant Squid

Ecological Relationshipgreat range of habitats from tropics to polar, altitudes exceeding 7000 m, ponds, lakes, streams, surf, ocean depths, etcMost live in the seaInclude herbivores, carnivores, and ciliary filter feedersOriginated in the seaEconomic Importancemany are food for humansproduce pearls (most from Eastern Asia)Some molluscs are destructive (Great Lakes, Snails and Slugs in gardens)

Form and FunctionBody Plan consist of head-foot portion and a visceral masshead-foot portion contains feeding, cephalic sensory, and locomotor organsvisceral mass contains digestive, circulatory, respiratory, and reproductive organs

Form and FunctionBody Plan two folds of skin make up a protective mantlethey enclose a space between the mantle and body wall called the mantle cavityit houses gills or lungsmantle also secretes a shell in many species

Form and FunctionHead-foot many have well developed head containing sensory organsrange from simple to complex eyesposterior of mouth is usually the foot (chief locomotor organ)

Form and FunctionHead-foot Unique structure inside mouth called radulaIt is a rasping, protrusible, tonguelike organ found in all molluscs except bivalvesIt is a ribbon-like membrane on which are mounted rows of tiny teeth that point backwardComplex muscles move the radula and its supporting cartilage (odontophore) in and out while the membrane is rotatedIt has about 250,000 teeth When protruded, it can scrape, pierce, tear, or cut food material

Radula (Slug Eating)

Form and FunctionHead-foot Foot can be adapted for locomotion, attachment, or a combination of functionsUsually a ventral, solelike structure in which muscular contractions create a creeping movementSome modifications include hatchet foot of bivalves, funnel for jet propulsion in squids and octopuses

Form and FunctionVisceral Mass (mantle and mantle cavity)mantle a sheath of skin extending from the visceral hump that hands down each side of the body, protecting soft parts and creating a spaceForm and FunctionVisceral Mass (mantle and mantle cavity)mantle cavity houses respiratory organsproducts from digestive, excretory, and reproduction systems empty into the mantle cavityin aquatic species, surface cilia create water currents that continually flush out waste

Form and FunctionVisceral Mass Shell (when present) typically has three layersPeriostracum outer organic layerComposed of a protein called conchiolinGrowth only occurs at the margin of the shellPrismatic layer middle layer Composed of densely packed prisms of calcium carbonate in a protein matrixNacreous layer Composed of calcium carbonate sheets laid down over a thin protein matrixThis layer is continuously secreted by mantle surface, so it becomes thicker during the animals lifeCalcium for the shell comes from environmental water, soil, or food

a. Periostracum, b1. Prismatic layer, b2. Nacreous layer

Form and FunctionInternal Structure and Function there is an open circulatory systempumping heartblood vessels blood sinusesmost cephalopods have closed circulatory system

Form and FunctionInternal Structure and Function Digestive tract is complex and highly specialized according to feeding habitsMost have a pair of kidneys (metanephridia)Ducts of kidneys in many forms serve to discharge eggs and sperm

Form and FunctionInternal Structure and Function Nervous System consists of several pairs of ganglia with connected nerve cordsMost molluscs are dioecious Some gastropods are hermaphroditicMany aquatic species pass through free-swimming trochophore and veliger larval stages

Trochophore

VeligerMating Leopard Slugshttps://www.youtube.com/watch?v=FhVi4Z6CjZk Class Polyplacophora: Chitonsare somewhat flattened and have a convex dorsal surface that bears eight plates, or valvesname means bearing many platesmost are between 2 and 5 cmcommonly occur on rocky surfaces in intertidal regionsif detached, they can roll up like an Armadillo for protectionSexes are separateEggs are released singly or in strings or masses of jelly

Class Gastropoda(gastro stomach, podos foot)By far the largest and most diverse classContains about 40,000 living speciesIncludes snails, limpets, slugs, whelks, conchs, periwinkles, sea slugs, sea hares, sea butterflies, etc.Often sluggish, sedentary animalsBecause of heavy shells and slow locomotor organs

Snails

Snails

Limpets (Owl Limpet)

Limpets

Slugs

Whelks

Whelks (Lightening)Conchs

ConchsConchs

Periwinkles

Periwinkles

Sea slugs

Sea slugs

Sea slugsFrosted Sea Slug

Sea hares

Sea hare

Sea hare

Sea butterfliesClass GastropodaBasically bilaterally symmetrical, but because of torsion, the visceral mass is asymmetricalTorsion a twisting process that occurs during development

Class GastropodaThree subclasses Prosobranchia (largest)Almost all marinePeriwinkles, limpets, whelks, conchs, abalones, slipper shells, oyster borers, rock shells, cowriesOpisthobranchiaSea slugs, sea hares, nudibranchs, canoe shellsPulmonataMostly land and freshwater snails and slugsUsually lack gillsMantle cavity becomes a lungUsually have two pairs of tentacles, with the posterior pair bearing eyes

Nudibranchs

NudibranchsClass Bivalvia (Pelecypoda)(two-shelled)Includes mussels, clams, scallops, oysters, shipwormsMost are sedentary suspension feedersUnlike gastropods they have no head, radula, and little cephalization

Class Bivalvia (Pelecypoda)Most are marine, but many live in brackish water and in stream, ponds, and lakesTheir two shells (valves) are held together dorsally by a hinge ligamentAdductor muscles work in opposition to the hinge ligament and draw the valves togetherZebra mussels (pg 194)

Zebra mussels (Lake Mead)Preventing Mussels in Idahohttps://www.youtube.com/watch?v=J4EVAy8adMk Class Cephalopodamost complex speciesinclude squids, octopuses, nautiluses, cuttlefishesAll are marineAll are active predatorsHave an odd body plan Develops as the embryonic head and foot become indistinguishableThe ring around the mouth bears arms and tentaclesClass CephalopodaRange from 2 to 3 cm to largest of all invertebrates (giant squid)Giant squid (pg 194)

Giant Squid

Slash marks from Giant SquidThe Search for the Giant Squidhttps://www.youtube.com/watch?v=EbubjXsA4S4 Class CephalopodaMost have special pigment cells called chromatophores in their skinBy expanding and contracting, they produce color changeSome color change are for protection to match the backgroundMost change is behavioral, associated with alarm or courtshipMany deep-sea squid are bioluminescentWhen the animal is alarmed, it releases a cloud of ink through the anus to form a smokescreen to confuse an enemy

SquidMimic Octopus and othershttps://www.youtube.com/watch?v=t-LTWFnGmeg&feature=related

Octopuses

OctopusesOctopuses

Blue Ringed OctopusThe most venous octopus. This small mollusc lives in warm, shallow reefs off the coast of Australia, new Guinea, Indonesia and the Philippines. It has a life span of about one and a half years.

Blue Ringed Octopus It is said that the venom of this octopus could kill 26 adults in just a few minutes. There is no antivenin for treatment. Fortunately, these octopuses do not attack humans. Injury typically occurs when a blue-ringed octopus is stepped on or picked up.87Smart Veined Octopus using Tools

Giant Pacific Octopus vs. Spiny Dogfish Shark

Nautiluses

Nautiluses

NautilusesChambered Nautilus

Diving for Nautilus

Cuttlefishes

Cuttlefishes

Cuttlefishes

Cuttlefish Attacks