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Phylum Molluscs. https:// www.youtube.com/watch?v=0a7j5prL8hc. General. Name means soft, or soft body this is one of the largest animal phyla, besides Arthropoda There are nearly 75,000 species and some 35,000 fossil species Very diverse group ( chitons , snails, clams, octopuses)
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Phylum Molluscs https://www.youtube.com/watch?v=0a7j5prL8hc
General Name means soft, or soft body this is one of the largest animal phyla, besides Arthropoda There are nearly 75,000 species and some 35,000 fossil species Very diverse group (chitons, snails, clams, octopuses) Range from simple organisms to some of the most complex invertebrates Size from microscopic to huge (18 m giant squid) 80% of molluscs are less than 5 cm
Molluscs Classes Class Polyplacophora: Chitons Class Gastropoda Class Bivalvia (Pelecypoda) Class Cephalopoda
Ecological Relationship great range of habitats – from tropics to polar, altitudes exceeding 7000 m, ponds, lakes, streams, surf, ocean depths, etc Most live in the sea Include herbivores, carnivores, and ciliary filter feeders Originated in the sea
Economic Importance many are food for humans produce pearls (most from Eastern Asia) Some molluscs are destructive (Great Lakes, Snails and Slugs in gardens)
Form and Function Body Plan – • consist of head-foot portion and a visceral mass • head-foot portion – contains feeding, cephalic sensory, and locomotor organs • visceral mass – contains digestive, circulatory, respiratory, and reproductive organs
Form and Function Body Plan – two folds of skin make up a protective “mantle” they enclose a space between the mantle and body wall called the “mantle cavity” it houses gills or lungs mantle also secretes a shell in many species
Form and Function Head-foot – many have well developed head containing sensory organs range from simple to complex eyes posterior of mouth is usually the foot (chief locomotor organ)
Form and Function Head-foot – Unique structure inside mouth called “radula” It is a rasping, protrusible, tonguelike organ found in all molluscs except bivalves It is a ribbon-like membrane on which are mounted rows of tiny teeth that point backward Complex muscles move the radula and its supporting cartilage (odontophore) in and out while the membrane is rotated It has about 250,000 teeth When protruded, it can scrape, pierce, tear, or cut food material
Form and Function Head-foot – Foot can be adapted for locomotion, attachment, or a combination of functions Usually a ventral, solelike structure in which muscular contractions create a creeping movement Some modifications include – “hatchet foot” of bivalves, funnel for jet propulsion in squids and octopuses
Form and Function Visceral 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 space
Form and Function Visceral Mass – (mantle and mantle cavity) mantle cavity – houses respiratory organs products from digestive, excretory, and reproduction systems empty into the mantle cavity in aquatic species, surface cilia create water currents that continually flush out waste
Form and Function Visceral Mass – Shell (when present) typically has three layers Periostracum – outer organic layer Composed of a protein called “conchiolin” Growth only occurs at the margin of the shell Prismatic layer – middle layer Composed of densely packed prisms of calcium carbonate in a protein matrix Nacreous layer – Composed of calcium carbonate sheets laid down over a thin protein matrix This layer is continuously secreted by mantle surface, so it becomes thicker during the animals life Calcium for the shell comes from environmental water, soil, or food
Form and Function Internal Structure and Function – there is an open circulatory system pumping heart blood vessels blood sinuses most cephalopods have closed circulatory system
Form and Function Internal Structure and Function – Digestive tract is complex and highly specialized according to feeding habits Most have a pair of kidneys (metanephridia) Ducts of kidneys in many forms serve to discharge eggs and sperm
Form and Function Internal Structure and Function – Nervous System consists of several pairs of ganglia with connected nerve cords Most molluscs are dioecious Some gastropods are hermaphroditic Many aquatic species pass through free-swimming “trochophore” and “veliger” larval stages
Mating Leopard Slugs https://www.youtube.com/watch?v=FhVi4Z6CjZk
Class Polyplacophora: Chitons are somewhat flattened and have a convex dorsal surface that bears eight plates, or valves name means “bearing many plates” most are between 2 and 5 cm commonly occur on rocky surfaces in intertidal regions if detached, they can roll up like an Armadillo for protection Sexes are separate Eggs are released singly or in strings or masses of jelly
Class Gastropoda (gastro – stomach, podos – foot) By far the largest and most diverse class Contains about 40,000 living species Includes snails, limpets, slugs, whelks, conchs, periwinkles, sea slugs, sea hares, sea butterflies, etc. Often sluggish, sedentary animals Because of heavy shells and slow locomotor organs
