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Chapter 12 www.emc.maricopa.edu Characteristics of Mollusca Protostomes - Embryonic blastopore becomes mouth, schizocoelous coelom formation and spiral embryonic cleavage. Have a coelom – fluid filled body cavity lined with mesoderm Head-foot – body part that contains head and is responsible for locomotion Land Slug cuttlefish More Characteristics of Mollusca Viseral mass – contains the organs of digestion, circulation, reproduction, and excretion Mantle – attaches to the viseral mass, may secrete a shell Mantle cavity – is between the mantle and the foot, functions in gas exchange, excretion, elimination, and release of reproductive products Most have a radula – contains rows of posteriorly curved teeth used to scrap and gather food. Open Circulatory System (except – Cephalopoda) Bilateral Symmetry Three Major Classes Class Gastropoda (snails, limpets, slugs) Austrorhytida capillacea Aequipenctin irradians Class Bivalvia (clams, oysters, mussels, scallops) Class Cephalopoda (octopuses, squid, cuttlefish, nautiluses) Hapalochlaena nierstraszi Other Classes of the Phylum Mollusca Class Polyplacophora Class Scaphopoda Class Monoplacophora Chiton Tusk Shell Neopilina Class Aplacophora Solenogaster Number of Species Relationships to Other Animals Protostomes Similarities in embryological development in mollusca and annelids ○ The Trochophore larvae stage is very similar and hard to distinguish Origin of the Coelom Schizocoelous coelom formation The splitting of mesoderm to form the coelom The Coelom is found in molluscan development as small cavities around the heart, pericardial cavity, the nephridia, and the gonads. Anatomical Features of Molluscs Three major Body Regions Head-foot Visceral mass mantle Anatomical Features of Molluscs Head-Foot The elongated portion with an anterior head, containing a mouth and certain nervous and sensory structures, and an elongated foot used for attachment and locomotion Anatomical Features of Molluscs Visceral Mass Contains the organs of digestion, circulation, reproduction, and excretion is found dorsal to the head-foot. Anatomical Features of Molluscs Mantle Usually attaches to the visceral mass and may secrete a shell Anatomical Features of Molluscs Mantle Cavity Opens to the outside of the body and functions in gas exchange, excretion, elimination of digestive waste and releases reproductive products. Anatomical Features of Molluscs Radula Consists of chitinous belt and rows of posteriorly curved teeth used to scrape food. Class Gastropoda The Snails, Limpets, and Slugs Limpet – Lottia insessa Snail - Bradybaena similaris Slug – Ariolimax californicas Class Gastropoda Largest class of molluscs Found in marine, freshwater, and terrestrial habitats Also found on plates in France Helix pomatia – French Delicacy Features of the Class Gastropoda Torsion – is the 180̊, counterclockwise twisting of the visceral mass, mantle and mantle cavity. This position twists the gills, anus, and openings from the excretory and reproductive systems just behind the head and nerve cord, and twists the digestive tract into a U shape. More on Torsion in Gastropods Torsion in gastropods Takes place in all gastropods usually during late veliger stage. Rotation of visceral mass and overlying mantle and shell 180o with respect to foot and head. Gut ends up U-shaped and incipient organs are switched left to right. Many gastropods remain torted. Opisthobranchs become detorted (untwist). 3 Advantages of Torsion 1. Allows the head to retreat into the shell first. Allowing the gastropod to protect its head from predators first. 2. Allows clean water to enter the anterior of the mantle cavity. 3. Allows the snail’s sensory organs to be orientated into the direction the snail is moving. Disadvantage of Torsion The anus and nephridia empty dorsal to the head The solution – some snails have notches or openings in the mantle that allow waste to exit posterior to the head The solution – some snails undergo detorsion by untwisting 90̊ allowing the mantle cavity to open to the right side of the body. Class Gastropoda – Shell Coiling Early fossils of gastropoda have a shell coiled in one plane creating a cumbersome shell. Modern snails are asymmetrically coiled into a more compact form. Achatina fulica – Giant African Snails Class Gastropoda - Locomotion Ciliated Flattened Foot, covered with Gland Cells. Small gastropods – use cilia to propel over mucus Larger gastropods – use waves of muscular contractions Aquatic gastropods modified foot for clinging. Limpets move through muscular undulations of the foot Class Gastropoda and Locomotion Gastropods and polyplacophorans. Crawling Direct and indirect waves. Mucus alternately acts as a glue and allows sliding. Some gastropods use cilia (moon snails). Class Gastropoda – Feeding and Digestion Most feed by scraping algae and small organisms from substrate using their radula Some are herbivores that feed on plants, scavengers, parasites, or predators Radula – Class Gastropoda (Left) Radula of the deep sea limpet, Neomphalus fretterae, Family Lepetidae (Right) Radula of the slit shell mollusc, Scissurella crispata, Family Scissurellidae Scanning electron micrographs; reprinted courtesy of Dr. Carole S. Hickman, Museum of Paleontology, University of California, Berkeley CA. Snail Radula in Action http://www.youtube.com/watch?v=mLVD wlrSq5U Class Gastropoda - Digestion The digestive tract is ciliated Food is suspended in a mucus mass called protostyle which extends into the stomach and is rotated by the cilia Enzymes are released from the digestive gland to process food. The intestines holds waste in the form of fecal pellets. Class Gastropoda – Other Maintenance Functions Gas Exchange Occurs in the mantle cavity ○ Modern gastropods have one gill – due to coiling ○ Siphon – is a rolled extension of the mantle Extends to the surface of the substrate to bring in water Land Snails – gills lost or reduced ○ Have richly vascular mantle for gas exchange with air Class Gastropoda – Other Maintenance Functions Open Circulatory System – Blood leaves vessels and directly washes over cells in the sinus spaces Heart consists of a single ventricle and two auricles – unless there is a shell (coiling) then one auricle Class Gastropoda – Other Maintenance Functions Hydraulic skeleton Gastropods contract muscles to push blood into structures that help push the snail forward Class Gastropoda – Other Maintenance Functions Sensory Structures Nervous system has 6 ganglia in the head and foot Osphradia – chemoreceptors anterior wall of mantle Eyes – may be at base or ends of tentacles ○ Simple photoreceptors ○ May consist of lens and cornea Class Gastropoda – Other Maintenance Functions Kidney Functions Modern Gastropoda have one nephridia that consists of a sac of highly folded walls where waste is modified and certain ions and organic molecules are reabsorbed. ○ Aquatic species excrete ammonia ○ Terrestrial snails convert ammonia to uric acid, less toxic and can be excreted in semisolid form to conserve water Class Gastropoda – Reproduction and Development Marine Snails – dioecious (separate males and female species) – discharge gametes into the sea for external fertilization. Here is a video of a Marine Snail Spawning: http://www.youtube.com/watch?v=KQdYDJU 3JHM Class Gastropoda – Reproduction and Development Terrestrial Snails – monoecious (hermaphroditic – having both male and female sex organs) Various forms of mating depends on species ○ Some internal some external ○ Some Develop as male first then later in life as female ○ Eggs need a moist place to mature Here is a Video of Terrestrial Snails Mating: http://www.youtube.com/watch?v=8ynjLPnF _2c&p=688A33FFB1266BA4&playnext=1&i ndex=6 Class Gastropoda - Development Marine Gastropods – Free Swimming trochophore larva Develop into free swimming veliger larva Veliger Larva – Have foot, eyes, tentacles and shell Torsion occurs during this stage Gastropod Diversity Subclass – Prosobranchia – 20,000 species Mostly Marine Species Gastropod Diversity Video: Nudibranchs http://www.youtube.com/watc h?v=nHVoV0MVwSc Subclass Opisthobranchia – less than 2,000 species Marine Slugs – foot modified as lobes for swimming Interesting Fact – Due to loss of shell some develop the defense system of acquiring undischarged nematocytsts from their cnidarian prey which they use to ward off predators Gastropod Diversity Subclass Pulmonata – 17,000 species Terrestrial and Marine snails and terrestial slugs Class Bivalvia 30,000 species Loss of radula and head Includes: Clams Oysters Bay Scallop Mussels Scallops Shell Consists of Two Valves Many are edible, some form pearls, valuable in removing bacteria from polluted water because they are filter feeders Class Bivalvia – Shell and Associated Structures Valves – Two Convex halves of the shell Hinge – on dorsal side Teeth – keep shell from twisting found on anterior end of shell Umbo – swollen area near shell’s anterior Embiologically shell forms as a single structure Near Hinge there is more protein than calcium carbonate, allows for muscular opening and closing of shell Class Bivalvia – Shell and Associated Structures Class Bivalvia – Shell and Associated Structures Adductor muscles at either end of the shell close the shell. This is important to defend against predators. Here are some clams escaping a predator: http://www.youtube.com/watch?v=ALaM oS_vvNE Class Bivalvia Pearl formation Shell Developing pearl Epithelium Irritant lodged between shell and mantle Layers of nacre secreted around foreign material 43 Class Bivalvia – Buried in sand Bivalves Burrowing Byssal threads Swimming Class Bivalvia – Gas Exchange Gills form folded sheets Cilia move water into the mantle cavity through an incurrent opening of the mantle. A siphon is an extension of the mantle and is a mechanism for buried bivalves to breath and filter feed. Class Bivalvia – Gas Exchange Siphons sticking above sand Class Bivalvia – Gas Exchange After entering the gills water moves into the vertical water channels in the gills called water tubes. Once in the water tubes the water with dissolved oxygen is in close proximity with the blood and diffusion takes place for the exchange of gases. Water exits through the excurrent opening in the mantle. Class Bivalvia - Feeding Suspended organic matter enters incurrent siphon. Gland cells on gills and labial palps secrete mucus to entangle particles. Food in mucous masses slides to food grooves at lower edge of gills. Cilia and grooves on the labial palps direct the mucous mass into mouth. Some bivalves feed on deposits in sand. Class Bivalvia – Nervous System Nervous system has three pairs of widely separated ganglia connected together. Sense organs are poorly developed. Statocysts in the foot. Osphradia in the mantle cavity (chemoreceptive). Pigment cells on the mantle. Some mantle eyes have a cornea, lens, retina and pigmented layer. Tentacles may have tactile and chemoreceptor cells. Class Bivalvia – Nervous System Scallops have a row of small blue eyes along the mantle edge. Each eye has a cornea, lens, retina, and pigmented layer. Class Bivalvia - Reproduction Bivalves usually have separate sexes. Zygotes develop into trochophore, veliger, and spat (tiny bivalve) stages. Class Bivalvia - Reproduction In freshwater clams, fertilized eggs develop into glochidium larvae which is a specialized veliger. Glochidia live as parasites on fish and then drop off to complete their development. Here is a video of a host being captured by a lure. The glochidia are injected into the host. http://www.youtube.com/watc h?v=BNKv07KjrFY&NR=1 Bivalve Diversity Live in nearly all aquatic habitats Can attach themselves using: Byssal threads Cementation Can burry into sand Some are boring and can secrete acid to create a home in limestone Ecological Impact of Non-native Species - Zebra Mussel Environmental Pest Ballast water of ships from Europe in 1986 Attack be secreting adhesive byssal threads Each other Other mussels Man made objects ○ Pipes, plumbing 54 Zebra Mussel Live in high densities Feed on phytoplankton Reproduce rapidly 55 Zebra Mussel Attach to native mussels Killed all native mussels in Lake Erie 56 Distribution of Zebra Mussel 57 Class Cephalopoda Includes Octopuses Cuttlefish Squid Cuttlefish Nautiluses Nautilus Squid – Humboldt octopus Class Cephalopoda The most complex molluscs Anterior portion of their foot modified into a circle of arms used for Prey capture Attachment Locomotion Copulation Foot is also incorporated into a foot used for jet like locomotion Class Cephalopoda Head is in line with the visceral mass Mantle is muscular and encloses all of the body except the head and tentacles. Acts as a pump to bring large quantities of water into the mantle cavity Class Cephalopoda Cephalopod fossils go back to Cambrian (570 mya) times. The earliest had straight cone-shaped shells. Later examples had coiled shells similar to Nautilus. Ammonoids were a very successful group, some had quite elaborate shells. Class Cephalopoda - Shells Shells of Nautilus and early nautiloid and ammonoid cephalopods were made buoyant by a series of gas chambers. Class Cephalopoda - Shells Nautilus shells differ from those of a gastropod because they are divided into chambers. The animal lives in the last chamber. A cord of living tissue extends through each chamber. Class Cephalopoda - Shells Cuttlefishes have a small curved shell, completely enclosed by the mantle. Cuttlebone from Cuttlefish shell Used to supplement birds tortoise diet with calcium Class Cephalopoda - Shells In squid, the shell has been reduced to a small strip called the pen, which is enclosed in the mantle. Class Cephalopoda Mantle Shell Absent in Octopus Class Cephalopoda - Locomotion Cephalopods swim by expelling water from the mantle cavity through a ventral funnel. They can aim the funnel to control the direction they are swimming. Normally they crawl over substrate Class Cephalopoda – Feeding and Digestion Locate their prey by sight and capture their prey with tentacles that have adhesive cups In squid the margins are reinforced with protein and sometimes possess small hooks Colossal Squid Tentacles Class Cephalopoda – Feeding and Digestion All have jaws (beak like structure for tearing food) and radula (rasps food) Colossal Squid Beak: Class Cephalopoda – Octopus Most Octopuses feed on snails, fish and crustasions They have salivary glands that inject venom into prey Check out the abilities of this octopus http://www.youtube.com/watch?v=Q36_ 8s5z6S8&feature=channel Class Cephalopoda Cephalopods have a closed circulatory system. Cephalopods exhibit greater excretory efficiency because of the closed circulatory system. A close association of blood vessels with nephridia allows waste to filter and secrete directly from the blood into the excretory system. Class Cephalopoda Nervous and sensory systems are more elaborate in cephalopods than in other molluscs. The brain is the largest of any invertebrate. Most cephalopods have complex eyes with cornea, lens, chambers, and retina. Class Cephalopoda – Communication Visual signals allow cephalopods to communicate. Movement of body and arms Color changes effected by chromatophores (cells in the skin containing pigment granules). ○ Chromatophores can change shape alternately dispersing and concentrating pigment. Cuttlefish and Camouflage http://www.youtube.com/watch?v=2x8v1mxpR0 Class Cephalopoda Most cephalopods have an ink sac that secretes sepia, a dark fluid containing the pigment melanin. When a predator tries to attack, the animal ejects the ink into the water where it hangs between the animal and the predator screening a quick escape. Octopus with secretes sepia Class Cephalopoda - Reproduction Sexes are separate in cephalopods. Juveniles hatch directly from eggs – no freeswimming larvae. One arm of male is modified as an intromittent organ, the hectocotylus. Removes a spermatophore from mantle cavity and inserts it into female. Cuttlefish and mating http://www.youtube.com/watch?v=fR7Dq f0vzzQ Squid in San Diago http://www.youtube.com/watch?v=sn7yx 3DFthI Interesting video about an Octopus and its features http://www.youtube.com/watch?v=4Tcnq 2iYJJo&feature=related Video from Discovery Mollusca Taxonomy Major classes Polyplacophora ○ Chitons Chiton tuberculatus lives in the rocky intertidal zones eat algae with its radula 8 shell plates Polyplacophoran Anatomy POLYPLACOPHORA - 800 species - primarily intertidal - restricted to rocky environment POLYPLACOPHORANS - EXTERNAL FEATURES - 8 plates embedded in a tough mantle - Mantle edge stiffened - called the girdle - The mantle may have spicules embedded in it. POLYPLACOPHORANS - EXTERNAL FEATURES girdle - Broad muscular foot - girdle and foot can act as suction cup - suction good to keep chiton attached to substrate (rocky shore) POLYPLACOPHORANS - EXTERNAL FEATURES girdle WATER FLOW: gills foot inhalent chamber: region between girdle and ctenidia. exhalent chamber: region of mantle cavity between ctenidia and foot, mantle cavity. HOW DO GILLS WORK? exhalent flow inhalent flow POLYPLACOPHORAN RADULA Iron oxides on teeth - Radular teeth have iron oxides on teeth - Iron oxides help teeth not wear down - Important on the rocky shore intertidal Chiton Spawning in Alaska http://www.youtube.com/watch?v=SvQcMbgUWU&feature=related Dioecious (have separate male and female sexes) Chiton Filtering Water http://www.youtube.com/watch?v=v3fljev ww9Y&feature=related Class Scaphopoda Called Tooth Shells or Tusk Shells All burrowing marine animals Conical shell that is open at both ends Head and foot can project from shell Incurrent and Excurrent allows water to enter and exit through apex of shell Have Radula and Tentacles Dioecious have separate sexes Class Monoplacophora Neopilina This class was only known from fossils until 1952 when Neopilina was dredged up from a depth of 3,520m off the Pacific Coast of Costa Rica. Have an Undivided Arch Shell Broad Flat foot Foot-retractor Muscle Serially repeated pairs of gills Dioecious Class Aplacophora Solengaster Divided into two subclasses Subclass Neomeniomorpha the solengasters lack a shell and crawl on their ventral surfaces Have a ladder like nervous system that suggests relations to the flatworms Subclass Chaetodermomorpha Wormlike molluscs live in ventrical burrows on the deep sea floor They have spicules on the body wall They lack the following molluscan traits: shell, crystalline style, statocysts, foot and nephridia Mollusc Phylogeny Mantle secreting shell Muscular foot Chambered heart Phylogeny The first molluscs probably arose during Precambrian times. Diverse molluscs found in the early Cambrian. It is likely that molluscs split off from the line that led to annelids after coelom formation, but before segmentation appeared. Phylogeny “Hypothetical Ancestral Mollusc” Probably lacked a shell or crawling foot. Probably small (about 1 mm). Likely was a worm-like organism with a ventral gliding surface. Probably possessed a dorsal mantle, a chitinous cuticle and calcareous scales. Reference Zoology by Miller and Harvey 6th Edition References – Pictures and diagrams cas.bellarmine.edu eol.org biology.ualberta.ca www.southtexascollege.edu science.kennesaw.edu elearning.najah.edu library.thinkquest.org Howstuffworks.com biology.fullerton.edu www.bumblebee.org More References depts.washington.edu reefkeeping.com snailstales.blogspot.com http://people.bu.edu/veliger/ www.geochembio.com http://cas.bellarmine.edu/tietjen/images/ phylum_mollusca.htm http://ofseaandshore.com/news/northse abeach/northseabeach.php