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5. Molluscs. Phylum Mollusca 200,000 species200,000 species –More species in ocean than any other animal group Soft body enclosed by calcium carbonate.

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Presentation on theme: "5. Molluscs. Phylum Mollusca 200,000 species200,000 species –More species in ocean than any other animal group Soft body enclosed by calcium carbonate."— Presentation transcript:

1 5. Molluscs

2 Phylum Mollusca 200,000 species200,000 species –More species in ocean than any other animal group Soft body enclosed by calcium carbonate shellSoft body enclosed by calcium carbonate shell Body covered by mantleBody covered by mantle –Thin layer of tissue that secretes the shell

3 Phylum Mollusca Displays Bilateral SymmetryDisplays Bilateral Symmetry Ventral muscular foot used for locomotionVentral muscular foot used for locomotion Most had have that includes eyes and other sensory organsMost had have that includes eyes and other sensory organs

4 Essentially, a mollusc is a coiled mass of vital organs wrapped in a dorsal shell.

5 Phylum Mollusca Some have radulaSome have radula –Ribbon of small teeth used to rasp food from surfaces –Made of chitin

6 What’s a radula and how does it work? Modern woodworkers could tell you! micrograph of a mollusc radula: note the chisel-like design

7 Phylum Mollusca Have paired gillsHave paired gills Portion of body may be coiled and asymetricalPortion of body may be coiled and asymetrical Occupy all marine environments – rocky shores to hydrothermal ventsOccupy all marine environments – rocky shores to hydrothermal vents

8 Essentially, a mollusc is a coiled mass of vital organs wrapped in a dorsal shell.

9 Gastropods (Class Gastropoda), or stomach foot,Gastropods (Class Gastropoda), or stomach foot, are the most common mollusks. are the most common mollusks. Snails, limpets, abalone, and nudibranchs.Snails, limpets, abalone, and nudibranchs. 75,000 spp.75,000 spp. nudibranch, Phidiana crassicornis Cooper’s nutmeg snail Cancellaria cooperi giant keyhole limpet Megathrua crenulata red abalone Haliotis rufescens Cone snail, Conus geographus

10 Class Gastropod – Stomach Footed Coiled mass of vital organs enclosed by a dorsal shell resting on a footCoiled mass of vital organs enclosed by a dorsal shell resting on a foot

11 Class Gastropod – Stomach Footed Most use radula to scrape algaeMost use radula to scrape algae Mud snails are deposit feedersMud snails are deposit feeders Whelks, oyster drills, and cone shells are carnivores that prey on clams, oysters, worms, and small fishesWhelks, oyster drills, and cone shells are carnivores that prey on clams, oysters, worms, and small fishes –Modified Radula to drill and rasp prey

12 Class Gastropod – Stomach Footed Nudibranchs (sea slugs)Nudibranchs (sea slugs) –No shell –Colorful branches of the gut and gills –Prey on sponges and other invertebrates –Produce noxious chemicals or retain undischarged nematocysts taken undigested from prey

13 Bivavles: Class Bivalvia

14 Class Bivalvia Clams, mussels, and oystersClams, mussels, and oysters Body laterally compressed and enclosed with two parts (valves)Body laterally compressed and enclosed with two parts (valves) No head or radulaNo head or radula Gills expanded and folded used to obtain oxygen, and filter and sort food particles from waterGills expanded and folded used to obtain oxygen, and filter and sort food particles from water

15

16 Scallops also filter feed. Many have striking color patters.

17 Class Bivalvia Inner surface of shell lined w/ mantle so whole body lies in mantle cavityInner surface of shell lined w/ mantle so whole body lies in mantle cavity Strong muscles used to close valvesStrong muscles used to close valves

18 Class Bivalvia Clams burrow in sand or mud and water drawn in and out of mantle by siphonsClams burrow in sand or mud and water drawn in and out of mantle by siphons –Allow clam to feed and obtain oxygen while buried

19 Class Bivalvia Mussels secrete byssal threads that attach them to rocks and other surfacesMussels secrete byssal threads that attach them to rocks and other surfaces

20 Class Bivalvia Oysters cement their left shell to hard surface and other to another oysterOysters cement their left shell to hard surface and other to another oyster –Pearls occur when irritating particles are lodged within the mantle cavity and covered by secretions (CaCO 3 ) from oyster

21 Class Bivalvia Some scallops can swim by rapidly ejecting water from mantle cavity with siphonSome scallops can swim by rapidly ejecting water from mantle cavity with siphon

22 Class Bivalvia Shipworm bores in mangroves, driftwood, and pilingsShipworm bores in mangroves, driftwood, and pilings –Have symbiotic relationship w/ bacteria in the gut that digests wood –Valves lie at the inner end of tunnel lined w/ calcium carbonate and siphon protrudes from entrance –Fouling organism = settles on bottoms of boats, pilings, and other submerged surfaces

23 Cephalopods “Putting Your Head and Feet Together”

24 Class Cephalopoda (head footed) Predators specialized in locomotionPredators specialized in locomotion Octopi, squid, and cuttlefishOctopi, squid, and cuttlefish Agile swimmers w/ complex nervous system and reduction or loss of shellAgile swimmers w/ complex nervous system and reduction or loss of shell All are marineAll are marine

25 Cephalopod (General Morphology) While still following the basic body plan of a mollusc, octopi are highly specialized.

26 Cephalopod (General Morphology) Large eyes on side of head Large eyes on side of head Thick muscular mantle which protects head Thick muscular mantle which protects head Water enters mantel and leaves through siphon = jet propulsion Water enters mantel and leaves through siphon = jet propulsion

27 Cephalopod: Octopi OctopiOctopi –Eight long arms (2 in to 30 feet) –Bottom dwellers that live in crevices, bottles, etc –Have beak-like jaws and radula to rasp flesh and secrete paralyzing substance –Distract predators with dark fluid from ink sac

28 Cephalopod: Squid SquidSquid –Two triangular fins on mantle – better swimmers than octopi –Can remain motionless, move forward, or backward –Eight arms and two tentacles, all with suckers –Has pen in upper surface of mantle –Few cm to 60 feet!!

29 Cephalopod: Cuttlefish CuttlefishCuttlefish –Eight arms and two tentacles, but body flatten w/ fin running along the body –Have calcified internal shell aids in buoyancy

30 Cephalopod: Chambered Nautilus Chambered NautilusChambered Nautilus –Coiled external shell containing gas filled chambers serves as buoyancy organ –Has suckerless tentacles

31 Other Molluscs Chitons (class Polyplacophora – bearer of many plates)Chitons (class Polyplacophora – bearer of many plates) –All marine –Eight overlapping shell plates covering dorsal surface –Live in shallow hard bottoms –Have radula to rasp algae

32 Other Molluscs Tusk shells or scaphopods (class Scaphopoda)Tusk shells or scaphopods (class Scaphopoda) –Elongated shell tapered at end resembling elephant tusk –Sandy muddy bottoms in deep water –Many species have thin tentacles to capture small prey Tusk shell hermit crab

33 Biology of Molluscs: Nervous System Gastropods and bivalves have ganglia (local brains) located in different parts of bodyGastropods and bivalves have ganglia (local brains) located in different parts of body

34 Biology of Molluscs: Nervous System CephalopodsCephalopods –Most complex of invertebrates –Brains coordinate and store information –Complex eye reflects development –Octopi and cuttlefish can learn

35 Biology of Molluscs: Nervous System CephalopodsCephalopods –Display rapid color change coordinated with behaviors and moods, from sexual display to camouflage –Cuttlefish “flash lights” while octopi change color and behavior to mimic poisonous fish and sea snakes 2011/where-s-the-octopus.html

36 Biology of Molluscs: Reproduction and Life History Most have separate sexes (some hermaphroditic)Most have separate sexes (some hermaphroditic) Bivalves, chitons, tusk snails, and some gastropods release sperm and egg into waterBivalves, chitons, tusk snails, and some gastropods release sperm and egg into water Cephalopods and most gastropods – internal fertilizationCephalopods and most gastropods – internal fertilization

37 Biology of Molluscs: Reproduction and Life History Cephalopods – modified arm to transfer spermatophoreCephalopods – modified arm to transfer spermatophore –Develop in yolk-filled eggs attached to crevices –Female dies – guarding eggs = no food Some have trochophore larvae, displaying relationship to segmented wormsSome have trochophore larvae, displaying relationship to segmented worms

38 Kings of Camouflage


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