Molluscs and Annelids (Mollusks) http://www.southplainscollege.edu/biology/swages/HICKMAN%20PP/MOLLUSCS_files/frame.htm

PHYLUM MOLLUSCA THE MOLLUSCS 2

What is a mollusk? Basic answer: Slugs, snails, and animals that once lived in shells in the ocean or on the beach are all mollusks.

INTRODUCTION Mollusca means “soft.” Most molluscs have shells for protection Eight diverse classes of molluscs with more than 100,000 named species Includes snails, clams, squids, octopuses, nautiluses, etc Found in almost all habitats. The need for calcium is a major limiting factor

Characteristics of Mollusk: An advanced nervous system Many types of feeders, including, carnivores, herbivores, filter-feeders and grazers. All but one class have a radula, a ribbon-like structure with teeth of chitin that scrapes, cuts or tears food Most molluscs are dioecious. They have a free-swimming trochophore larva; many also have a veliger larva stage

CHARACTERISTICS, Cont. An advanced nervous system Many types of feeders, including, carnivores, herbivores, filter-feeders and grazers. All but one class have a radula, a ribbon-like structure with teeth of chitin that scrapes, cuts or tears food Most molluscs are dioecious. They have a free-swimming trochophore larva; many also have a veliger larva stage

CHARACTERISTICS, Cont. Durable shells found in marine, freshwater, and terrestrial habitats One of the most successful of all phyla – only arthopods have more terrestrial species Important food source for humans Coelom – very important 2 body opeings

Not entirely beneficial Economic importance – pearls mother –of –pearl jewelry and other jewelry Food source Not entirely beneficial - shipworms – destructive to timber submerged in sea slugs, terrestrial snails can cause extensive damage to flowers, gardens an crops hosts to intermediate stages for many serious diseases

Body size

External body plan Some mollusks have shells Some are adapted to live without a hard covering (slugs and squids) Bivalve – 2 shelled mollusks (clams oysters, scallops)

External body plan - bivalve Umbo Growth lines Ventral side – Dorsal side

UMBO tells direction Anterior Posterior Dorsal Ventral

NO CEPHALIZATION (No head) Shell = valve (Bivalves = 2 shells) Growth rings Adults = sessile (stay in one place)

Internal body plan - bivalve Siphon Exhalent Inhalent Adductor muscle Distinct bilateral symmetry Visceral mass Muscular foot Mantle gills

THE MOLLUSCS 15

VISCERAL MASS Contains heart, digestive, excretory, reproductive

INCURRENT & EXCURRENT SIPHONS move food up toward mouth CILIA on gills pull in water

Describe the function of gills

GILLS Trap food (PALPS move it forward) Ridges for more surface area (like typholosole) Gas exchange Diffusion moves oxygen & carbon dioxide across membrane

Mollusc shell Secreted by mantle Protects the 2 underlying layers form erosion Pearls

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Describe the different functions of the mantle ( include the role of the continuous stream of water) Some molluscs can withdraw into mantle davity for protection In aquatic molluscs a continuous stream of water is passed into and out of this cavity by the cilia on the gills This action brings in oxygen and in the case of bivalves food Carries out waste material In squids and octopuses the mantle cavity has been modified to create the jet propulsion system that enables these animals to move rapidly through the water.

ADDUCTOR MUSCLES Turn POSTERIOR END toward door Cut your adductor muscles to open shell

Functions of the foot

Describe how molluscs obtain food

Circulatory system in molluscs Open system of circulation Closed circulatory system heart

OPEN CIRCULATION Blood flows loose inside coelom and tissue spaces Reduced Coelom = pericardial cavity (space around heart)

Excretion in molluscs REFER TO PREVIOUS DIAGRAM

Respiration in molluscs

NERVOUS SYSTEM 2 pairs of nerve cords 3 pairs of ganglia http://www.student.loretto.org/zoology/Graphic%20webs/Clam-%20nervous%20system.htm 3 pairs of ganglia 2 pairs of nerve cords

Reproduction in Molluscs TROCHOPHORE LARVA VELIGER LARVA BACK THE MOLLUSCS 32

CLASSIFICATION Of the 8 mollusc classes, we’ll look at 3: Class Polyplacophora- the chitons Class Scaphopoda- the tooth shells Class Gastropoda- the snails Class Bivalvia- the clams, oysters Class Cephalopoda- octopuses, squids

Three main classes of molluscs

Gastropoda

CLASS GASTROPODA The snails, slugs, whelks, limpets, conchs, periwinkles and others Largest, most diverse group of molluscs One-piece shell, usually coiled Mostly herbivores; radula for feeding Land and freshwater gastropods have lungs

THE MOLLUSCS 37

THE MOLLUSCS 38

SEA SLUG: CLASS GASTROPODA THE MOLLUSCS 39 SEA SLUG: CLASS GASTROPODA

Bivalvia

CLASS BIVALVIA Have 2 shells Includes clams, oysters, scallops and mussels Sedentary filter-feeders. The only molluscan group with no radula

THE MOLLUSCS 42 A GIANT CLAM

THE MOLLUSCS 43

Cephalopoda

CLASS CEPHALOPODA The squids, octopuses and nautiluses Among the most advanced of all invertebrates Active predators living in the ocean, which requires them to be fast, smart, coordinated and possess good eyesight They have a funnel-like structure allowing for movement by jet propulsion Arms and/or tentacles for grasping. The tentacles have suckers

CEPHALOPOD SHELLS Only the members of the genus Nautilus possess an external shell. Unlike the shells of gastropods nautiloid shells are divided by septa into a series of chambers. The animal lives only in the outer chamber Cuttlefish have an internal chambered shell Squids have a small internal sheet-like shell Octopuses have no shell

CEPHALOPOD EYESIGHT Nautiloids have relatively poor eyesight compared to other cephalopods Other cephalopods have image-forming eyes similar to mammals, but they evolved separately (convergent evolution). Cephalopod eyes possess structures similar to mammalian eyes, but they focus differently

THE MOLLUSCS 48

SQUID THE MOLLUSCS 49

THE MOLLUSCS 50 AN OCTOPUS

OCTOPUS THE MOLLUSCS 51

THE MOLLUSCS 52 Nautilus Anatomy

Nautilus BACK THE MOLLUSCS 53

Reproduction in Cephalopods Sexes are separate Sperms stored in spermatophores – a sac that opens into mantle cavity Male uses a tentacle to transmit spermatophore from cavity into female cavity Female fertilizes eggs as they leave the oviduct Attach to stones or other objects