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Phylum Mollusca Chapter 13: Phylum Mollusca pp. 329-334 Biology fun facts of the day: Experts claim that about 1,000 oysters must be opened in order to find one usable pearl! Biology fun facts of the day: The common garden snail, Helix aspersa, can travel about 2 feet in 3 minutes. At that rate, it would travel 1 mile in 5.5 days. (Now you know where the term ‘snail mail’ comes from!) Biology fun facts of the day: When we hold a large seashell up to our ear, you can hear what sounds like waves because the shell echoes all the sounds around you. If you could listen to a shell in a completely soundproof room, you would hear nothing at all! Biology fun facts of the day: Many land snails can lift 10 times their own weight up a vertical surface. (If you were this strong, and you weighed 30 kg (about 70 lb), you could carry 300 kg (almost 700 pounds!!!) straight up a wall! Introduction to Molluscs Molluscs represent the second largest animal phylum, following the arthropods = Old Phylum (500 million years, approx.) 80,000 – 100,000 existing species (estimate) Most species are free-living Inhabit a variety of marine, aquatic & terrestrial habitats Important ecological roles with regards to nutrient recycling; bivalves clean and recycle sediments Empty shells provide habitat for other invertebrates Where do Molluscs fit in? Introduction to Molluscs Phylum Mollusca – Latin molluscus = “soft” Protostomes Bilateral symmetry; eucoelomates 3 cell layers (ectoderm, endoderm, mesoderm) Have a coelom (but often reduced to a cavity that surrounds only the heart) Have trochophore larvae (free-swimming ciliated larva) • Similar larvae in annelids likely share a common ancestor Introduction to Molluscs Molluscs all share similar developmental patterns and a common body plan: Foot (muscle; function varies) Shell (protection; made of CaCO3) Mantle (produces the shell) Visceral mass (contains internal organs) Diagrams of snail, clam, and squid p. 300 Classes of Molluscs 1) Class Bivalvia • 2 hinged shells • No head or eyes • Gills; live in water Example members: clams, oysters, scallops 2) Class Gastropoda • One shell • Some are terrestrial Example members: snails, slugs, nudibranchs Classes of Molluscs 3) Class Cephalopoda Fast-moving predators Foot is modified into tentacles Well-developed nervous system Some can use camouflage and jet propulsion (e.g. octopus) when they feel threatened Example members: octopus, squid, nautilus, cuttlefish Nautilus Octopus Squid Squid are the largest Cephalopods Colour and Morphology Changes = Camouflage Form and Function of Molluscs Molluscs vary a lot clam = representative mollusk Digestive system: • Complete digestive tract (mouth anus) • Mouth, esophagus, stomach, intestine, anus • Have a radula (scraping/drilling organ) or a beak (cephalopods) • Bivalves trap food in their gills – no radula e.g. Gastropod Form and Function of Molluscs Respiratory system: • Aquatic mollusks have gills • Terrestrial mollusks have a highly folded mantle for O2/CO2 exchange (must stay moist) *A clam has incurrent and excurrent siphons sea water passes through; location of gas exchange Circulatory system: • Open circulatory system – the heart pumps blood through open spaces called sinuses instead of through blood vessels Excretory system: • Nephridia (primitive kidneys) remove metabolic waste (nitrogen-containing wastes like NH3) • Digestive wastes go out anus Nervous system: • Bivalves – reduced nervous system; no head • Gastropods – fairly basic • Cephalopods – very well developed • Good vision, small ganglia near mouth, statocysts (balance), simple chemical and touch receptors • Good dexterity and memory – they can learn! Musculoskeletal system: • Muscular foot for movement • Bivalves – “two shell”; foot pulls animal forward, and can be sucked back in (for protection) • Gastropods – “stomach foot”; they slide forward on broad ventral foot (use muscus) • Cephalopods – “head foot”; foot has been modified into many tentacles with suction cups e.g. Gastropod Reproduction: • Some Monoecious (have both sex organs, capable of producing both sperm and eggs) • Others are Dioecious (either male or female gonads, can produce one type of gamete only) • Separate sexes (usually) • External fertilization (broadcast method) in bivalves/marine gastropods) the female traps sperm • Internal fertilization in cephalopods/terrestrial gastropods Ecology of Molluscs Bivalves used to check pollution levels – “environmental monitors” Range of lifestyles: predators, scavengers, filter feeders, etc. Crop damage – slugs, snails on land Ship damage – shipworms in water Food source for humans: clams, oysters, mussels, etc. • Humans can get poisoned by eating mollusks contaminated with toxic protists cause “red tide” Molluscs Movie! Mollusc (5-7-5) Haiku: Slow, slick, sliding slug Terrestrial explorer No protective shield Create your own mollusc haiku in 5-7-5 format! Works Cited Images taken from the following sources: http://other95.blogspot.com/2007/10/circus-of-spineless26-like-being-home.html http://offthemark.com/search-results/key/mollusk/ http://kevinmainjewelry.blogspot.com/2010/06/pearl-funfacts-and-care-tips.html http://seashellvilla.com/advertise_here.html http://www.zazzle.com/snail_mail_postcard239469706654312651 http://bio1151b.nicerweb.com/Locked/media/ch32/trocho phore.html http://www.education.com/study-help/article/biology-helpmollusks-clam-up-would-ya/ Works Cited http://www.thecanadianencyclopedia.com/index.cfm?PgNm =TCESearchMedia&Params=A1&MediaId=385 http://perfectgardeningtips.com/category/plants/pestcontrol/ http://www.apartmenttherapy.com/sf/insects-pests/slugs082896 http://birdhouse.org/blog/2008/05/16/nudibranchs/ http://www.zazzle.com/i_squid_cephalopods_tshirt235319078835508111 https://www.mentalfloss.com/blogs/archives/58856 http://radio-weblogs.com/0105910/2004/01/10.html http://ihatetheocean.blogspot.com/2010/08/august-6-2010nautilus.html http://zollberg.co.cc/bivalve.html Works Cited http://js082.k12.sd.us/My_Classes/Advanced_Biology/Ch_25 /Clam%20Dissection/Clam_Dissection.htm http://www.sciencewithme.com/learn-about-mollusks/ http://www.bio.miami.edu/dana/106/106F06_12.html http://nashzoology.ning.com/forum/topics/molluskclassificationchoose?commentId=2223964%3AComment%3A10692&x g_source=activity http://sharon-taxonomy2009-p3.wikispaces.com/Mollusca http://www.lifeinfreshwater.org.uk/Web%20pages/ponds/Poll ution.htm http://www.nero.noaa.gov/nero/hotnews/redtide/ http://www.sheppardsoftware.com/content/animals/profile_ mollusks.htm