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Molluscs Bonneville High School Vertebrate Zoology CHAPTER 16 16-1 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Unit Objectives Objective 1: Describe the form and function of the Molluscs Objective 2: Differentiate between the classes of Molluscs (Caudofoveata, Solenogastres, Monplacophora, Polyplacophora) Objective 3: Differentiate between the classes of Molluscs: (Scaphopoda, Gastropoda, Bivalvia, Cephalopoda) Objective 4: Describe the Internal form and function of

gastropods, bivalves, and cephalopods. Objective 5: Describe the form and function of the Annelida Objective 6: Differentiate between the classes of Annelida (Polychaeta, Oligochaeta, Hirudinea, ) Objective 7: Describe the Internal form and function of the following classes: Polychaeta, Oligochaeta, Hirudinea. Objective 8: Describe the life cycle and reproductive strategies for Molluscs and Annelids 16-2 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fluted Giant Clam 16-3

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Characteristics Phylum Mollusca 16-4 Over 90,000 living species and 70,000 fossil species Soft body and protostomes Include chitons, tusk shells, snails, slugs, nudibranchs, clams, mussels, oysters, squids, octopuses, and nautiluses

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Marine Snail Chiton Nudibranch Pacific Giant Clam Octopus 16-5 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Characteristics

Characteristics: Herbivorous grazers, predaceous carnivores, filter feeders, and parasites Most are marine, but some are terrestrial or freshwater aquatic 16-6 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-7 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Characteristics Evolution

Fossil evidence Some bivalves and gastropods Limited to moist, sheltered habitats with calcium in the soil Cephalopods

16-8 Moved to brackish and freshwater Snails (gastropods) successfully invaded land Indicates molluscs evolved in the sea Most have remained marine Evolved to become relatively intelligent Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Characteristics Economics 16-9 Many are used as food Culturing of pearls is an important industry Snails and slugs are garden pests Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Form and Function Mollusc Body Plan: Head-Foot and Visceral Mass Portions Head-foot region contains feeding, sensory, and locomotor organs (foot) Visceral mass contains digestive, circulatory, and reproductive organs Mantle Cavity 16-10

Space between mantle (sheath of skin) and body wall is the mantle cavity Mantle cavity houses the gills or a lung In most molluscs Mantle secretes a shell over the visceral mass Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Generalized Mollusk Anatomy 16-11 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Form and Function

Radula 16-12 Unique to molluscs Found in all except bivalves Protruding, rasping, tongue-like organ Ribbon-like membrane has rows of tiny teeth (up to

250,000) pointed backward Radula rasps off particles of food from surfaces Serves as a conveyor belt to move particles to digestive tract New rows of teeth replace those that wear away Pattern and number of teeth are used in classification of molluscs Some specialized to bore through hard material or harpoon prey Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Radula 16-13 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Form and Function Foot Functions in attachment or locomotion Modifications include Hatchet foot of clams

Siphon jet of squids Secreted mucus aids in adhesion or helps molluscs glide Snails and bivalves extend the foot by engorgement with blood Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Form and Function Shell If present, secreted by the mantle

Periostracum Middle prismatic layer Closely packed prisms of calcium carbonate Increases with animal growth Inner nacreous layer

16-15 Outer layer - wears away Composed of hardened protein Next to the mantle; the nacre is laid down in thin layers Aids in Pearl formation Shiny layer in abalone, nautilus, and bivalve Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A.Bivalve Shell B. Pearl Formation from a parasite or sand that enters shell into mantle, becomes covered with nacre

16-16 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Form and Function Reproduction and Life History Most dioecious, some hermaphroditic (monoecious) Egg hatches and produces a free-swimming trochophore larva In many gastropods and bivalves Trochophore is followed by intermediate larval stage, the veliger.

16-17 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Internal Form and Function (Obj 4)

-Torsion: A twisting process that makes the Mollusc visceral mass asymmetrical. -Coiling: The spiral winding of the shell and visceral mass. It is NOT the same as torsion. -Ctenidium: Located in the mantle cavity, this acts as gills for some Molluscs -Lung: A highly vascular area in some Molluscs which aids in respiration it has an opening called a pneumostome. -Dioecious: Having male and female gonads in separate individuals. -Monoecious: Having both male and female gonads in the same organism: Hermaphrodite -Pulmonates: Molluscs which show detorsion and include land and most fresheater snails and slugs. They lost their ctenidia and their vascularized mantle wall has become a lung. They are monoecious. -Chromatophores: Cells in the skin that contain pigment granules. This can change the color of the skin of some mollusks. They are used for camouflage and communication.

-Ink gland: A gland which most cephalopods and nautiloids have that secretes sepia, a dark fluid containing the pigment melanin. The pigment is deposited into an ink sac that empties into the rectum. The Mollusc can then release the dark cloud to confuse or distract a predator. Open circulatory system: a pumping heart, blood vessels and blood sinuses. Blood is pumped from the heart into open spaces. Closed circulatory system: Closed circulatory systems have the blood closed at all times within vessels of different size and wall thickness. In this type of system, blood is pumped by a heart through vessels, and does not normally fill body cavities. 16-18 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Trochophore larva 16-19 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Classes of Molluscs Class Monoplacophora-Neopilina Class Polyplacophora Chitons Class Caudofoveata-Chaetodermomorpha Class Solenogastres-Solenogastres Class Scaphopoda-Tusk or tooth shells

Class Gastropoda - Slugs, Snails, Nudibranch Class Bivalvia - Clams, Mussels Class Cephalopoda - Squid, Octopus, Nautilus Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Monoplacophora

Body bilaterally symmetrical with broad, flat foot; A single dome-shaped shell Five or six pairs of gills in shallow mantle cavity Radula present Separate sexes. Example: Neopilina 16-21 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Classes of Molluscs Class Polyplacophora: Chitons Chitons are somewhat flattened with 7or 8 dorsal plates Most prefer rocky intertidal surfaces Chiton radula is reinforced with iron mineral Scrapes algae from the rocks 16-22 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-23

Mossy Chiton - hairs and bristles aid in defense Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Caudofoveata

Wormlike Shell, head and excretory organs absent Radula usually present Mantle with chitinous cuticle and calcareous scales Sexes separate Was united with solenogasters but now classified separately Examples Chaetoderma, Limifossor Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Solenogastres

Solenogasters Wormlike Shell, head, and excretory organs absent; radula usually absent Mantle covered with scales or spicules;

Hermaphrodite Example: Neomenia 16-25 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Scaphopoda

Tusk Shells Body enclosed in a one piece, tubular shell open at both ends. Conical foot; Mouth with radula and tentacles, head absent Sexes are separate Example: Dentalium 16-26 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Gastropoda

Class Gastropoda Most diverse class Over 70,000 living Forms range from marine forms to airbreathing terrestrial snails and slugs Shells, if present, are chief defense Some produce distasteful or toxic

secretions Use process of Torsion 16-27 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Classes of Molluscs Gastropod Shells

One-piece (univalve) Apex is smallest and oldest whorl Whorls become larger and spiral around central axis Giant marine gastropods have shell up to 60 cm long 16-28 Some fossil forms are 2 meters long Terrestrial gastropods shells are restricted by soil mineral content, temperature, dryness, and acidity

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-29 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Gastropoda Cont. Form and Function 16-30

Torsion Developmental process that changes the relative position of the shell, digestive tract and anus Digestive tract moves so that anus lies above head Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Gastropoda Cont. Coiling Coiling or spiral winding of the shell and visceral mass not the same as torsion 16-31

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Abalone Feed on kelp -herbivore Moon Snail feeds on clams and mussels Radula releases chemicals to soften shell, so they can get to their prey 16-32 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Conus - Extends proboscis

to capture prey. Then releases Conotoxins to paralyze (lethal to Humans) Hours later regurgitate scales and bones 16-33 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Gastropoda Cont Internal Form and Function

Respiration performed by vascular area in mantle cavity that serves as lung Most have a single nephridium (kidney) and welldeveloped open-circulatory and nervous systems 16-34 Sense organs include eyes, statocysts, tactile organs, and chemoreceptors Eyes vary from simple cups holding photoreceptors to a complex eye with a lens and

cornea. (On tentacle of some) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-35 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Gastropoda Cont Reproduction: 16-36

Eggs emitted singly or in clusters, and may be transparent or in tough egg capsules Young may emerge as veliger larvae or pass this stage inside the egg Some species, including most freshwater snails, are ovoviviparous Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Eggs of Mollusks Eggs - resemble grains of wheat 16-37 Egg ribbon of Nudibranch

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Classes of Molluscs Major Groups of Gastropods Traditional classification has recognized three subclasses of Gastropoda Prosobranchia, Opisthobranchia Pulmonata 16-38

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gastropods - Prosobranchia Includes most marine snails Have one pair of tentacles, separate sexes Diodora aspera Hole in Apex for water to leave 16-39 Flamingo Tongue Snails

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Opisthobranches: sea slugs, sea hares, sea butterflies, and nudibranch Marine, Shell is reduced or absent 2 tentacles, Sea Hare 16-40 Sea Hares defense mechanism- a secretion from its purple gland Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-41 Nudibranch - calcareous spicules for protection

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonates - Snail and Banana slug 2 tentacles: posterior have eyes Opening to Mantle Cavity 16-42 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Classes of Molluscs Class Bivalvia

Mussels, clams, scallops, oysters Range in size from 12 mm in length to the giant South Pacific clams (1m) Most are sedentary filter feeders Bivalves lack a head, radula, or other aspects of cephalization Contain Siphons 16-43 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mussels Scallops

Escaping a Sea Star 16-44 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-45 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Northwest Ugly Clams Siphons Incurrent brings in Food and Oxygen 16-46

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Bivalvia Form and Function 2 shells or valves are held together by a hinge ligament Valves are drawn together by strong adductor muscles Umbo is the oldest part of the shell with growth

occurring outward in rings Posterior edges of the mantle folds form excurrent and incurrent openings 16-47 In burrowing clams, mantle forms long siphons to reach the water above Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Bivalvia Locomotion

16-48 Foot is extended out from between the valves Blood is pumped into the foot Foot swells and anchors the bivalve in the mud Shortening of the foot pulls the clam forward Scallops clap valves to create a jet propulsion Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-49

Scallop - developed sensory organs along mantle edges (tentacles and blue eyes) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Bivalvia Gills Both mantle and gills perform gaseous exchange Siphon used in respiratory

Water enters incurrent siphon Gas diffused out Exits through the excurrent siphon Circulatory - Open circulatory system 16-50 3 chambered heart has two atria and one ventricle Blood vessels line gills to receive oxygen Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16-51 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-52 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Shipworm BivalvesBurrows into wood on docks and piers 16-53 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clam Symbiotic relationship

with Algae to gain most nutrients Siphonal Area 16-54 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Bivalvia Reproduction and Development

Sexes usually separate Gametes discharged in excurrent flow Fertilization usually external Embryos develop as trochophore, and veliger larval stages Freshwater clams have internal fertilization Larvae develop into a bivalved glochidia stage 16-55

Sperm enter the incurrent siphon to fertilize eggs in water tubes of the gills Attaches to gills of passing fish where they live briefly as parasites Hitchhiking having helped distribute the species Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-56 Life Cycle of an Oyster Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glochidium - freshwater clam larva Attach to fishs gills by clamping their valve closed.

Stay for several weeks. Pocketbook Mussel mimics a small minnow, when a Smallmouth Bass comes to dine, it releases its glochidia 16-57 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Cephalopoda Class Cephalopoda Squids, octopuses, nautiluses, and cuttlefish

All marine predators Foot is in the head region Range from 2 cm to the giant squid (60 ft) Modified for expelling water from mantle cavity Largest invertebrate Nautilus - only one with external shell

16-58 Series of gas chambers in shell helps maintain neutral buoyancy Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nautilus A. Feed on a Fish 16-59 B. Showing Gas filled chambers Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-60

Cuttlefish Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Cephalopoda Locomotion 16-61

Cephalopods swim by forcefully expelling water through a ventral funnel or siphon Control direction and force of the water, thus determining its speed Lateral fins of squids and cuttlefishes are stabilizers Nautilus swims mainly at night Octopuses mainly crawl on the bottom but can swim Some with webbing between their arms swim with a medusa-like action Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Squid - Pen is only remains of shell 16-62

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Cephalopoda Respiration and Circulation With higher oxygen demands, cephalopods have a muscular pumping system to keep water flowing through the mantle cavity Circulatory system has a network of vessels conducting blood through gill filaments (Closed Circulatory System!!) 16-63 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Class Cephalopoda Nervous and Sensory Systems 16-64 Cephalopod brain is the largest of any invertebrate Squids have giant nerve fibers

Sense organs are well-developed Eyes are complex, complete with cornea, lens, and retina Can learn by reward and punishment, and by observation of others Cephalopods lack a sense of hearing but have tactile and chemoreceptor cells in their arms Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cuttlefish Eye 16-65 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Cephalopoda

Communication 16-66 Use chemical and visual signals to communicate Chromatophores are cells in the skin that contain pigment granules Contractions of the muscle fibers attached to the

cell causes the cell to expand and change the color pattern Color patterns can be changed rapidly Deep-water cephalopods have elaborate luminescent organs Ink sac empties into rectum; (Not in Nautiloids) Contains ink gland that secretes sepia (dark fluid) when animal is alarmed Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Cephalopoda Reproduction

16-67 Sexes are separate In male seminal vesicle, spermatozoa are packaged in spermatophores and stored One arm of male is modified as an intromittent organ, the hectocotylus Removes a spermatophore from mantle cavity and inserts it into female Fertilized eggs leave oviduct and are attached to stones, etc. Large, yolky eggs undergo meroblastic cleavage (not full

cleavage) Hatch into juveniles with no free-swimming larval stage Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copulation in Cephalopods Male Octopus uses modified arm 16-68

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