2Phylum Mollusca 200,000 species More species in ocean than any other animal groupSoft body enclosed by calcium carbonate shellBody covered by mantleThin layer of tissue that secretes the shell
3Phylum Mollusca Displays Bilateral Symmetry Ventral muscular foot used for locomotionMost had have that includes eyes and other sensory organs
4Essentially, a mollusc is a coiled mass of vital organs wrapped in a dorsal shell.
5Phylum Mollusca Some have radula Ribbon of small teeth used to rasp food from surfacesMade of chitin
6What’s a radula and how does it work? Modern woodworkers could tell you! micrograph of a mollusc radula: note thechisel-like design
7Phylum Mollusca Have paired gills Portion of body may be coiled and asymetricalOccupy all marine environments – rocky shores to hydrothermal vents
8Essentially, a mollusc is a coiled mass of vital organs wrapped in a dorsal shell.
9Gastropods (Class Gastropoda), or stomach foot, are the most common mollusks.Snails, limpets, abalone, and nudibranchs.75,000 spp.red abaloneHaliotis rufescensgiant keyhole limpetMegathrua crenulataCooper’s nutmeg snailCancellaria cooperinudibranch, Phidiana crassicornisCone snail, Conus geographus
10Class Gastropod – Stomach Footed Coiled mass of vital organs enclosed by a dorsal shell resting on a foot
11Class Gastropod – Stomach Footed Most use radula to scrape algaeMud snails are deposit feedersWhelks, oyster drills, and cone shells are carnivores that prey on clams, oysters, worms, and small fishesModified Radula to drill and rasp prey
12Class Gastropod – Stomach Footed Nudibranchs (sea slugs)No shellColorful branches of the gut and gillsPrey on sponges and other invertebratesProduce noxious chemicals or retain undischarged nematocysts taken undigested from prey
14Class Bivalvia Clams, mussels, and oysters Body laterally compressed and enclosed with two parts (valves)No head or radulaGills expanded and folded used to obtain oxygen, and filter and sort food particles from water
16Scallops also filter feed. Many have striking color patters.
17Class BivalviaInner surface of shell lined w/ mantle so whole body lies in mantle cavityStrong muscles used to close valves
18Class BivalviaClams burrow in sand or mud and water drawn in and out of mantle by siphonsAllow clam to feed and obtain oxygen while buried
19Class BivalviaMussels secrete byssal threads that attach them to rocks and other surfaces
20Class BivalviaOysters cement their left shell to hard surface and other to another oysterPearls occur when irritating particles are lodged within the mantle cavity and covered by secretions (CaCO3) from oyster
21Class BivalviaSome scallops can swim by rapidly ejecting water from mantle cavity with siphon
22Class Bivalvia Shipworm bores in mangroves, driftwood, and pilings Have symbiotic relationship w/ bacteria in the gut that digests woodValves lie at the inner end of tunnel lined w/ calcium carbonate and siphon protrudes from entranceFouling organism = settles on bottoms of boats, pilings, and other submerged surfaces
23“Putting Your Head and Feet Together” Cephalopods“Putting Your Head and Feet Together”
24Class Cephalopoda (head footed) Predators specialized in locomotionOctopi, squid, and cuttlefishAgile swimmers w/ complex nervous system and reduction or loss of shellAll are marine
25Cephalopod (General Morphology) While still following the basic body plan of a mollusc, octopiare highly specialized.
26Cephalopod (General Morphology) Large eyes on side of headThick muscular mantle which protects headWater enters mantel and leaves through siphon = jet propulsion
27Cephalopod: Octopi Octopi Eight long arms (2 in to 30 feet) Bottom dwellers that live in crevices, bottles, etcHave beak-like jaws and radula to rasp flesh and secrete paralyzing substanceDistract predators with dark fluid from ink sac
28Cephalopod: Squid Squid Two triangular fins on mantle – better swimmers than octopiCan remain motionless, move forward, or backwardEight arms and two tentacles, all with suckersHas pen in upper surface of mantleFew cm to 60 feet!!
29Cephalopod: Cuttlefish Eight arms and two tentacles, but body flatten w/ fin running along the bodyHave calcified internal shell aids in buoyancy
30Cephalopod: Chambered Nautilus Coiled external shell containing gas filled chambers serves as buoyancy organHas suckerless tentacles
31Other Molluscs Chitons (class Polyplacophora – bearer of many plates) All marineEight overlapping shell plates covering dorsal surfaceLive in shallow hard bottomsHave radula to rasp algae
32Other Molluscs Tusk shells or scaphopods (class Scaphopoda) Elongated shell tapered at end resembling elephant tuskSandy muddy bottoms in deep waterMany species have thin tentacles to capture small preyTusk shell hermit crab
33Biology of Molluscs: Nervous System Gastropods and bivalves have ganglia (local brains) located in different parts of body
34Biology of Molluscs: Nervous System CephalopodsMost complex of invertebratesBrains coordinate and store informationComplex eye reflects developmentOctopi and cuttlefish can learn
35Biology of Molluscs: Nervous System CephalopodsDisplay rapid color change coordinated with behaviors and moods, from sexual display to camouflageCuttlefish “flash lights” while octopi change color and behavior to mimic poisonous fish and sea snakes
36Biology of Molluscs: Reproduction and Life History Most have separate sexes (some hermaphroditic)Bivalves, chitons, tusk snails, and some gastropods release sperm and egg into waterCephalopods and most gastropods – internal fertilization
37Biology of Molluscs: Reproduction and Life History Cephalopods – modified arm to transfer spermatophoreDevelop in yolk-filled eggs attached to crevicesFemale dies – guarding eggs = no foodSome have trochophore larvae, displaying relationship to segmented worms