Phylum Mollusca

This phylum is referred to as the ______ invertebrates. All members have a _______ , although most have a ______ that protects them.

"soft-bodied", soft body, hard shell

Nudibranchs

(a) Commonly called sea slugs nudibranchs are marine gastropods that lack a shell. (b) Gas exchange occurs across the entire body surface of the nudibranch. (c) The body surface is covered with many fingerlike extensions that increase the surface area for gas exchange (d) The foot is modified into a wing like flap that is used for swimming, rather than crawling. (e) Some nudibranchs contain chemicals that taste bad or are poisonous. These nudibranchs are usually brightly colored to serve as a warning to potential predators.

Slugs

(a) Slugs are terrestrial. They look like snails but without the shells. (b) Like snails, they respire through the lining of their mantle cavity. (c) To avoid dehydration, they hide in moist and shady places during the day, and feed at night. (d) A slime gland secretes a path of mucous in front of the animal. The slug slides over the slime. (This is also true of land snails.)

Clams Food Getting and Digestion

1. Bivalves are filter feeders. They are the only mollusks without a radula 2. Beating cilia causes water to enter the clam through the incurrent siphon and leave the clam through the excurrent siphon 3. As water cycles through the clam, the water is filtered for small organisms and organic debris. The filtered material becomes trapped on the sticky gills Cilia then push the food toward the mouth 4. The palps help to direct the food into the mouth 5. Food enters the stomach 6. The digestive gland secretes enzymes into the stomach and digestion is completed. 7. In the intestive the digested food is absorbed into the bloodstream 8. Wastes pass to the anus

Clams Nervous System

1. Bivalves lack a distinct head and there are no specialized sense organs 2. There are three pairs of ganglia one pair near the mouth one pair in the digestive system and one pair in the foot 3. The ganglia are connected by nerve cords 4. sensory cells are located at the edge of the mantle These sensory cells send information to the ganglia that allows the clam to respond to touch or chemicals in the water

Cephalopod Circulatory System

1. Cephalopods have a closed circulatory system .The circulation of blood is enclosed inside a system of blood vessels 2. A closed circulatory system transports fluid more quickly than an open circulatory system. Therefore, nutrients, oxygen, and carbon dioxide are carried more quickly to and from the tissues of the body. This increases the activity level of the organism.

Gastropods undergo a process called "torsion" during larval development:

1. During torsion, the visceral mass twists around 180 degrees in relation to the head. This brings the mantle cavity, gills, and anus to the front of the animal 2. Because of torsion, a gastropod can withdraw its head into its mantle cavity when threatened. 3. Note: The coiling of the shell is unrelated to torsion.

The 3 classes of mollusks

1. Gastropoda 2. Bivalvia 3. Cephalopoda

Gills

1. Gills are specialized for the exchange of gases 2. Gills have a large surface area in contact with a rich supply of blood vessels. Oxygen from the water diffuses into the blood vessels of the gills. Carbon dioxide in the blood diffuses across the surface of the gills into the external environment. 3. Aquatic mollusks possess gills. Land dwelling mollusks do not have gills or lungs. In land dwelling mollusks oxygen diffuses across thin, moist membranes to enter the body.

The body generally consists of three regions:

1. Head: contains the mouth and sensory organs 2. Foot: a large muscular organ used for locomotion 3. Visceral Mass: Contains all of the internal organs 4. Since the mollusks have a true coelom, all organ systems are well developed.

Characteristics of class Bivalvia

1. Includes clams oysters, muscles and scallops 2. They are known as bivalves because their shell is divided into two halves 3. A hinge connects the two valves. 4. They are able to open and close their shells by using powerful adductor muscles that are attached to the inside surface of each valve. When the adductor muscles contract the valves close. When the adductor muscles relax the valves open. 5. The valve (or shell) consists of three layers that are secreted by the mantle a) The thin outer layer protects the shell against acidic conditions in the water b) The thick middle layer is composed of calcium carbonate and strengthens the shell c) The smooth inner layer protects the soft body of the animal

In an open circulatory system

1. Instead of blood, the circulatory fluid is called hemolymph 2. The hemolymph does not remain enclosed inside a system of blood vessels 3. Hemolymph is collected from the lungs or gills where it is oxygenated pumped through the heart, and released into spaces within the tissues of the body. 4. These fluid filled spaces are known as a hemocoels, or blood cavities 5.From the hemocoel, the hemolymph returns via the gills or lungs to the heart.

Clams respiration and circulation

1. Like the gastropods, the bivalves have an open circulatory system. 2. Water passing over the gills exchanges oxygen and carbon dioxide with the hemolymph

Nervous System

1. Mollusks have ganglia which serve as a primitive brain. 2. The ganglia are connected by two pairs of nerve cords. 3. The ganglia and nerve cords control the muscles involved in movement and feeding. 4. The nervous system allows the mollusk to respond to simple stimuli such as light, touch, and chemical in the environment.

What roles do mollusks play in the ecosystem?

1. Mollusks play an important role in food chain by serving as food for other organisms. Humans consume clams, scallops, oysters, mussels, and snails 2. The filter-feeding mollusks "clean up" their surroundings by filtering algae out of the water or by feeding on detritus. 3. Some mollusks are hosts to symbiotic algae or to parasites 4. Because filter-feeding mollusks collect pollutant and microorganisms in their body tissues, they can be used to monitor water quality 5. Some mollusks are used for research purpose. These mollusks do not appear to develop any form of cancer. Scientists study them for this reason to gain information on how to fight cancer in humans.

Movement of the Clam

1. Most bivalves are sessile. Sessile means that the organism is attached to one spot and not moving 2. Some species extend their muscular foot into the sand. The muscle contracts pulling the clam down into the sand. 3. Adductor Muscles: allow the clam to open and close shells

Clams Reproductive System

1. Most clams have spate sexes 2. In marine clams, sperm and eggs are released into the water and fertilization occurs externally 3. In freshwater clams, eggs are fertilized internally by sperm that enter through the incurrent siphon The larvae are discharged into the water through the excurrent siphon 4. The fertilized egg develops into a torchophore larva This larva is free swimming but eventually settles to the bottom and develops into an adult

Snails

1. Snails are gastropods that can live on land, in fresh water, and in salt water 2. Snails have delicate tentacles on their heads. Eyes, located at the tips of these tentacles, help snails to locate food. 3. Aquatic snails get oxygen and release carbon dioxide through gills. 4. In land snails, the mantle cavity acts as a modified lung. Oxygen and carbon dioxide are exchanged through the thin membrane that lines the mantle cavity. This membrane must be kept moist. As a result, land snails are active at night and remain hidden during the day.

The Cephalopod Nervous System

1. The cephalopod brain is the largest and most advanced brain of any of the invertebrates. 2. The octopus can learn to solve simple problems, can perform simple tasks, and can learn to differentiate between objects. 3. Cephalopods have well developed eyes that are capable of forming images of objects.

Class Gastropoda members include:

1. The mollusks with one shell: Snails, abalones, and conchs 2. The mollusks with no shell: Nudibranchs and slugs 3. Gastropods move by using a muscular foot located on the ventral side.

Octopus

1. The octopus has 8 tentacles 2. Most octopuses average 3 feet or less in length. The giant Pacific octopus may reach 30 feet.

Radula

1. The radula is the main feeding adaptation in many mollusks. 2. It is a flexible, tongue-like structure with abrasive teeth that point backward. 3.It is used to cut food or to scrape food from a surface.

The squid

1. The squid are cephalopods with 10 tenacles 2. The two longest tentacles are used for capturing prey and the other 8 are used to force the prey into the mouth 3. Most squid grow to about one foot in length, but the giant squid may reach a length of 60 feet. The giant squid, Architeuthis, is the largest known invertebrate.

The Cephalopod Reproductive System

1. There are separate sexes. The male transfers packets of sperm from his mantle cavity to the mantle cavity of the female, where fertilization occurs. 2. The female lays masses of fertilized eggs and she guards the eggs until they hatch. 3. Eggs hatch into juveniles. There is no larva

The trochophore larva:

1. This is a larval stage of development, a common feature shared by most aquatic mollusks and annelids 2. The trochophore hatches from the egg and is a free-swimming larva. It has cilia used for movement and for drawing food into its mouth. 3. Trochophores are carried on ocean currents and help in the dispersal of their species. 4. Since this trochophore larva is found in both mollusks and annelids it suggests that these two groups may have evolved from a common ancestor

Chambered Nautilus

1. This is the only cephalopod that has retained its shell. 2. The shell is spiraled and is divided into a series of gas filled chambers. The soft body of the nautilus is confined to the outermost chamber. As it grows, it moves forward in its shell, and fills the chamber left behind with gas. The gas makes the nautilus buoyancy

This phylum has over ______ different species. Only the phylum ______ has more species.

112,00, Arthropoda

The Class Cephalopoda

A. Members of this class include: octopus, stupid, chambered nautilus, cuttlefish B. These organisms are specialized for a free swimming and predatory life C. Characteristics of the class Cephalopoda. 1. The cephalopod body consists of a head and a single foot. The foot has been divided into tentacles The tentacles have powerful suction cups to grasp objects and capture prey 2. Cephalopods kill and eat their prey with the help of a pair of jaws that looks like the beak of a parrot. 3. Many cephalopods can release a cloud of link into the water to distract predators. 4. They contain chromophores These are pigment cells that change color allowing the cephalopod to blend in with the surroundings.

Animals in this phylum include

Clams, Oysters, Mussels, Scallops, Snails, Slugs, Nudibranchs, Octopus, Squid, Chambered nautilus

Phyla having a true coelom are:

Mollusca, Annelida, Arthropoda, Echinodermata, Chordata

The mantle is

a layer if epidermal tissue that cover the visceral mass

Animals that are coelomates have

a true coelom

The advantages to having a true coelom:

a) The muscles of the body wall are separated from those of the gut. The body wall muscles can contract without hindering the movement of food through the gut b) A coelom provides a space where the circulatory system can transport blood without interference from the internal organs c) The gut and other internal organs are suspended from the body wall and are cushioned by the fluid within the coelom

The roundworms are called pseudocoelomates

because their body cavities are only partially lined with mesoderm tissue.

Mollusks have _______. This term means ________ shape. Organisms with bilateral symmetry have a ________. There is only one way to divide the organism to get two equal sides.

bilateral symmetry, "two-sided", right and a left side

Mollusks are

coelomates

A coelom is a

hallow fluid-filled body cavity that is completely lined with mesoderm tissue.

In most mollusks, the mantle secretes one or more______ composed of_______.

hard shells, calcium carbonate

Class Gastropoda

is the largest and most diverse class of mollusks, consisting of 65,000 different species.

Gastropods have an _____ circulatory system

open

the shell

protects the soft body of the mollusk

The disadvantage of a shell is that it

reduces the surface area available for the exchange of gases such as oxygen and carbon dioxide. This disadvantage was overcome by the evolution of gills.

The mollusks are the only coelomates that do not have

segmented bodies

Phylum Mollusca is a very diverse group of invertebrates. Some are _____ and others are _____.

stationary filter feeders, fast-swimming predators

all organ systems are

suspended within this coelom

The mollusks are divided into 7 classes based on

the characteristics of the foot and the shell.

The flatworms are called acoelomates because

they have no body cavity at all. The three germ layers are packed one on top of the other without any cavity in between them.