Section 1 Mollusca Chapter 35 Characteristics of Mollusks • PhylumMollusca is a diverse group of invertebrates such as clams, snails, slugs, squids, and octopuses. • They are called mollusks, from the Latin molluscus, which means “soft.” Many mollusks have soft bodies and some have a hard shell. • Some mollusks are sedentary filter feeders, while others are fast-moving predators. • Mollusks are coelomates. • Most aquatic mollusks and annelids have a larval stage called a trochophore.

Section 1 Mollusca Chapter 35 Body Plan of Mollusks • The body of a mollusk is generally divided into: • the visceralmass, which contains the heart and the organs of digestion, excretion, and reproduction • the head-foot, which consists of: • the head, which contains the mouth and sensory structures • the foot, a large, muscular organ for locomotion • The coelom is limited to a space around the heart. • A layer of epidermis called the mantle covers the visceral mass.

Section 1 Mollusca Chapter 35 Body Plan of Mollusks, continued • In most mollusks, the mantle secretes one or more hard shells containing calcium carbonate. • This disadvantage of a shell is offset by having gills. • The gills are protected within the mantle cavity. • Most mollusks are bilaterally symmetrical. • The nervous system consists of paired clusters of nerve cells called ganglia. • The main feeding adaptation of many mollusks is the radula.

Section 1 Mollusca Chapter 35 Class Gastropoda • The largest and most diverse class of mollusks is Gastropoda, whose members are called gastropods. • Most gastropods, including snails, abalones, and conchs, have a single shell. Others, such as slugs and nudibranchs, have no shell. • Gastropods undergo the process of torsion during larval development. • Gastropods have an open circulatory system in which a heart pumps hemolymph from gills or lungs into the hemocoel.

Section 1 Mollusca Chapter 35 Class Gastropoda, continued Snails • Snails live in moist and aquatic environments. • Most snails locate food using eyes at the end of tentacles. • Snails survive dry periods by retreating into their shells and sealing the opening with a mucous plug. Other Gastropods • Slugs are terrestrial and lack shells. • Nudibranchs are marine and lack shells. • Pteropods, or “sea butterflies,” have a foot that is modified into a winglike flap and used for swimming rather than crawling.

Section 1 Mollusca Chapter 35 Class Bivalvia • The class Bivalvia includes aquatic mollusks such as clams, oysters, and scallops. • They are called bivalves because their shell is divided into two valves connected by a hinge. • Each valve consists of three layers. • Most bivalves are sessile filter feeders. • Bivalves lack a distinct head and have three pairs of nerve ganglia.

Section 1 Mollusca Chapter 35 Class Bivalvia, continued Clams • Clams are bivalves that live buried in mud or sand. • The mantle cavity of a clam is sealed except for a pair of hollow, fleshy tubes called siphons. • Water enters through the incurrent siphon. • Water leaves through the excurrent siphon. Other Bivalves • Oysters become attached to a hard surface early in their development. • Scallops can move through the water by repeatedly opening their valves and snapping them shut.

Section 1 Mollusca Chapter 35 Class Cephalopoda • The class Cephalopoda includes octopuses, squids, cuttlefishes, and chambered nautiluses. • They are called cephalopods, which means “head-foot.” • They are specialized as free-swimming predators. • They have tentacles and beaklike jaws on the head. • Their nervous system is very advanced. • They have a closed circulatory system. • Many use pigments to hide and disguise themselves.

Section 1 Mollusca Chapter 35 Class Cephalopoda, continued Squids • Squids are cephalopods with ten tentacles. • They propels themselves by pumping jets of water with the mantle through an excurrent siphon. Octopuses • Octopuses have eight tentacles and are similar to squids. • They often crawl along the ocean bottom or lie in wait for prey. Chambered Nautiluses • The chambered nautilus is the only existing cephalopod that has retained its external shell. • The shell is coiled and divided into a series of chambers. The body is confined to the outermost chamber.

Section 1 Mollusca Chapter 35 Mollusk Body Plan

Section 1 Mollusca Chapter 35 Characteristics of Mollusks Click below to watch the Visual Concept. Visual Concept

Section 1 Mollusca Chapter 35 Anatomy of a Trochophore Click below to watch the Visual Concept. Visual Concept

Section 1 Mollusca Chapter 35 Anatomy of a Mollusk Click below to watch the Visual Concept. Visual Concept

Section 1 Mollusca Chapter 35 Radula Click below to watch the Visual Concept. Visual Concept

Section 1 Mollusca Chapter 35 Types of Mollusks Click below to watch the Visual Concept. Visual Concept

Section 1 Mollusca Chapter 35 Characteristics of Gastropods

Section 1 Mollusca Chapter 35 Anatomy of a Snail Click below to watch the Visual Concept. Visual Concept

Section 1 Mollusca Chapter 35 Characteristics of Bivalves

Section 1 Mollusca Chapter 35 Anatomy of a Clam Click below to watch the Visual Concept. Visual Concept

Section 1 Mollusca Chapter 35 Characteristics of Cephalopods

Section 2 Annelida Chapter 35 Objectives • Identifythe structures that provide the basis for dividing annelids into three classes. • Listthe advantages of body segmentation. • Describethe structural adaptations of earthworms. • Comparethe three classes of annelids.

Section 2 Annelida Chapter 35 Characteristics of Annelids • The phylum Annelida is made up of bilaterally symmetrical, segmented worms. • This phylum includes common earthworms, feather-duster worms, and bloodsucking leeches. • They are called annelids,which means “little rings” and refers to the many body segments. • Annelids have a true coelom that is divided into separate compartments by partitions. • Most annelids have external bristles called setae(singular, seta), and some have fleshy protrusions called parapodia (singular, parapodium).

Section 2 Annelida Chapter 35 Class Oligochaeta • Annelids of the class Oligochaeta generally live in the soil or in fresh water and have no parapodia. • Oligochaeta means “few bristles”; these annelids have a few setae on each segment. • The most familiar member is the earthworm. Structure and Movement • An earthworm’s body has over 100 nearly-identical segments. • Circular and longitudinal muscles line the interior body wall. • Locomotion is made possible by segmentation.

Section 2 Annelida Chapter 35 Class Oligochaeta, continued Feeding and Digestion • Earthworms ingest soil as they burrow through it. • Soil is moved through these structures: • mouth • pharynx • esophagus • crop • gizzard • intestine • includes the typhlosole • anus • Earthworms play an important role in the condition of soil.

Section 2 Annelida Chapter 35 Class Oligochaeta, continued Circulation • Contractions of the aorticarches and the dorsal blood vessel force blood through the closed circulatory system. Respiration and Excretion • Oxygen and carbon dioxide diffuse through the skin, which contains many small blood vessels and must be kept moist. • Cellular wastes and excess water are excreted through nephridia. Neural Control • The nervous system of an earthworm consists of a chain of ganglia connected by a ventral nerve cord. • Sensory structures are found in all segments but are concentrated at the anterior end.

Section 2 Annelida Chapter 35 Class Oligochaeta, continued Reproduction • Earthworms are hermaphrodites, but an individual worm cannot fertilize its own eggs. • During mating, earthworms press their ventral surfaces together. • They are held together by their setae and by a film of mucus secreted by each worm’s clitellum. • The sperm from each worm move through the mucus to the seminal receptacle of the other. • The clitellum secretes a tube of mucus and chitin. • Fertilization occurs inside the tube, which forms a protective case for the young worms.

Section 2 Annelida Chapter 35 Class Polychaeta and Hirudinea • Most annelids are members of the class Polychaeta, which means “many bristles.” • Polychaetes differ from other annelids in that they have antennae and specialized mouthparts. • They are the only annelids that have a trochophore stage. • Hirudinea is the smallest class of annelids, consisting of about 500 species of leeches. • Leeches have no setae or parapodia. • Many leeches are carnivores but some are parasites that suck blood from other animals.

Section 2 Annelida Chapter 35 Anatomy of the Earthworm

Section 2 Annelida Chapter 35 Characteristics of Annelids Click below to watch the Visual Concept. Visual Concept

Section 2 Annelida Chapter 35 Segmentation Click below to watch the Visual Concept. Visual Concept

Section 2 Annelida Chapter 35 Types of Annelids Click below to watch the Visual Concept. Visual Concept

Section 2 Annelida Chapter 35 Anatomy of an Earthworm Click below to watch the Visual Concept. Visual Concept

Section 2 Annelida Chapter 35 Movement of an Earthworm Click below to watch the Visual Concept. Visual Concept

Section 2 Annelida Chapter 35 Feeding Habits of an Earthworm Click below to watch the Visual Concept. Visual Concept

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