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Lab 15 - Animal Diversity Intro - Clams (Part 1 of 5)

By Kathy Egbert
Last updated about 5 years ago
58 Questions

Last Name, First Name

Class Period:

Date:

Note the classification heiarchy (1 through 7 in Fig 15.2) corresponds with the items on the next page, 183, Table 15.1

2: Germ layers; 3:Symmetry; 4: Body Plan; 5:Coelom; and 6: Segmentation

Specimen provided:
Chiton, Katharina tunicata

Class:

Description of Foot:

Cephalization:

Specimens provided:
Land Snail Helix aspersa

Class

Description of Foot:

Cephalization:

Specimens provided:
Clam Venus mercenaria, scallops

Class:

Description of Foot:

Cephalization:

Specimen provided:
Squid Loligo brevipenna

Class:

Description of Foot:

Cephalization:

Mollusks - Review Mollusks are tasty. They are also fairly diverse. There are about 100,000 different extant species and 35,000 extinct ones. The reason why we can identify so many extinct species is because most mollusks have some sort of shell that mineralizes very easily. It leaves a great fossil. Mollusks have been dated to 600 MYA.
Classification
  • Kingdom Animalia
  • Subkingdom Eumetazoa - mollusks have organs
  • Branch Bilateria - they have bilateral symmetry
  • Grade Coelamata - they have body cavities
  • Subgrade Schizocoela - the mesoderm pouches to form that body cavity
  • Class Polyplacophora - "bearer of many plates"
  • Class Pelecypoda - "hatchet footed"
  • Class Gastropoda -"stomach footed"
  • Class Cephalopoda -"head footed"
A Look At Each Class:
Class Polyplacophora The typical example is a CHITON, a small ovular species with eight plates on its dorsal side (back). It has:
  • an open circulatory system. An open circulatory system is one in which the tissues are bathed directly by the blood. The heart (or equivalent structure) pumps the blood into an artery. The artery takes the blood to the tissue, where it returns to the heart via a vein. In advanced animals, like humans, the blood goes from the heart to an artery, to a capillary (the name for a very small blood vessel) to the cells (by way of diffusion) and back to the heart through a vein. This is important because as a rule, creatures with open circulatory systems aren't all that large. Why? Because without a very efficient way of getting blood to cells, you simply can't maintain a large body mass. You simply can't get blood to all the tissues fast enough.
  • RADULA - a rasping tongue. This acts like a scraper when the chiton preys on algae who live on rocks.
  • Chitons are GONOCHORISTIC. This just means that there are male chitons and female chitons. The sexes are separate.
  • Its digestive system is as follows: Mouth, Esophagus, Stomach, Intestine, Rectum, Anus. Know "Mesira" and know her well. She is a good friend.
Class Pelecypoda These are the tasty ones. This group includes mussels, clams and oysters. They are called "bivalves" because their shell is made up of two hinged segments. They don't move very far from their homes on the bottom of the various bodies of water they inhabit. Like other mollusks, these things have huge amounts of GONADS - why? Because they aren't built like other animals. They can't copulate like other animals can. They have external fertilization. They spew large amounts of sperm and eggs throughout the water and hope that they meet. It doesn't seem very efficient but that also explains why clams and other mollusks live in beds. A group of these things got together and thats where mating occured and thats where the next generation was born. They don't move great distances but they DO move around. Zebra mussels for instance, are just about everywhere in this part of the world. As larvae, they can swim, so they can inhabit other lakes and rivers. They clog up intakes and are just a plain nuisance. They also have cleared Lake Erie tremendously. In doing so, they've altered the food web and are outcompeting native specimens. Not bad for a mussel who wasn't even in North America until less than 15 years ago.

Class Gastropoda Snails are the archetypical example of gastropods. Snails are noteworthy in that they are NOT gonochoristic. They share all the typical "molluscian" traits with chitons - the shell, the mantle, the radula, the open circulatory system etc. In addition, they are HERMPAPHRODITIC. There is no such thing as a male snail or a female snail. When they mate, they pick who will be the male and who will be the female.

Class Cephalopoda Cephalopods are the most "advanced" of the mollusks. Squids and octopi are the prime example of cephalopods. They have a closed circulatory system so they can move much faster - the closed circulatory system allows more efficient "pinpointing" of blood. Squid also have the largest nerve fibers in the animal kingdom. This enables them to move pretty quick. Squid can hit speeds of about 15 meters PER SECOND in short bursts (~50% faster than a world-class olympic sprinter). They move through jet propulsion - water is taken in and expelled under pressure. Squid also are notable for their eyes. Their eyes are very similar to that of the vertebrates. This is an example of convergent evolution - two species distantly related moving closer together.

Next is a video stepping you through the dissection. Start and stop it as needed as you complete the worksheet that follows the video.
Clam Dissection video/instructions about 10 mins; first external identification and then internal identification
Dissection Guide and Worksheet for the Clam (Mussel)
Mollusks are soft-bodied invertebrates. They have a muscular foot and a mantle. In most mollusks, the mantle secretes ahard shell. In this investigation you will observe the external and internal structures of a representative mollusk--the clam or fresh-water mussel. Clams are pelecypods, or bivalves, and have a two-part hinged shell. Clams are found in fresh water in streams, ponds, and lakes. They also are very common burrowed into the mud of ocean mud flats. Clams are often used for food.
Clams belong to the phylum Mollusca. Molluscs (Latin molluscus, "soft"), as the origin of the name suggests, are soft-bodied animals having an internal or external shell. Included in the phylum are snails, oysters, slugs, clams, octopuses, and squids. Most molluscs are bilaterally symmetrical (have a left and right side) and have well-developed respiratory, excretory, circulatory, and digestive systems. Some may have a calcareoushell surrounding the body mass.
Molluscs are similar to annelids in their development. Both have trochophore larvae. Molluscs differ from annelids, however, in the absence of segmentation. Further, the coelom, so prominent in the annelids, is greatly reduced in the molluscs and is generally restricted to an area surrounding the heart.
Most molluscs are slow moving, but the bodies of several species have been highly modified for rapid locomotion. Although primarily marine organisms, some molluscs are found in fresh water (clams and snails) and on land (snails and slugs).
The molluscs are characterized by having three main body regions: a head-foot, which is the sensory and locomotive part of the body; a visceral mass containing the excretory, digestive, and circulatory organs; and the mantle, which secretes the shell. The gills, which function in respiration, are located inside the mantle.

To what phylum does the clam belong?

What does the name of the phylum translate (from the Latin language) to mean?

Six common members of the phylum Mollusca are: snails, oysters, slugs, clams, octopuses, and squid.

Bilateral symmetry means that the left and right sides are different, but parallel to each other.

The major component of a calcareous shell is...

The three main body regions of a mollusk are: head-foot, visceral mass, and the mantle.

The classification shown above is for the specific clam you are dissecting. Clams belong to the Class Pelecypoda (which means "hatchet foot"). Members of the Class Pelecypoda provide delight for epicureans, jewelers, and artisans the world over, because they provide food, pearls, and mother-of-pearl, which can be fashioned into hundreds of forms. Another name for this group is "bivalves," as they possess two shells or valves. Included in the group are clams, oysters, mussels, scallops, and shipworms. They vary in size from one centimeter across up to well over one meter (the Giant Clam of the South Pacific). Since clams and mussels are found both in salt and fresh water, they are common throughout the United States and the entire world.

To what Class does the clam belong?

The Class name for clams translates from Latin to mean "flat foot".

Bivalve means that an organism has two shells or valves.

Five common members of the Class Pelecypoda are: clams, oysters, mussels, scallops, and shipworms.

Obtain a preserved clam and rinse it thoroughly to remove excess preservative. Place the clam in a dissecting tray.

Observe the bivalve shell. Notice the hinge ligament. The small, pointed area near the hinge ligament is called the umbo. It is the oldest part of the clam. The umbo is situated dorsally toward the anterior end of the clam and is surrounded by concentric growth lines. The lines represent alternating periods of slow and rapid growth.

The oldest part of the clam shell is called the...

Sometimes this is difficult, however, attempt to count the number of concentric growth lines on the shell. (This is similar to counting tree rings.) Your estimate is...

Before you continue with this investigation, it is important to know the orientation of the clam shell. Recall that the umbo is near the anterior end. The posterior of the clam shell is at the opposite end. In reference to the clam shell, dorsal is the side, or edge, with the umbo. Ventral is the side, or edge, opposite the umbo. Locate the posterior, anterior, dorsal, and ventral surfaces of your clam shell. Hold the clam shell with the anterior end up and the hinge facing toward you. Locate the posterior, anterior, right valve, and left valve of the clam shell.
Correctly match the numbered labels in the figure above with these terms: dorsal, ventral, anterior, posterior, right valve, left valve, umbo, hinge, and concentric growth lines. Numbers 3 and 6 are used twice because they identify the same term from two different views.

#1 is the

#2 is the

#3 is shown in two different view of the clam. It is the

#4 is pointing to the lines on the outside of the clam shell which are concentric growth lines.

#5 is the

#6 is showing the same location from two different views of the clam shell . It is the

#7 is pointing to the left side valve.

#8 is pointing to the hinge.

#9 is pointing to the left side valve.

Skills assessment, 9 pts: Once you feel comfortable identifying the external structures, ask the teacher to come and verify your identification of the external parts of the clam.

Hold the clam in the dissecting tray as shown in the figure above. With a scalpel carefully scrape, away some of the horny outer layer of the shell. Scrape until you see the "white part" (prismatic layer) of the shell (it does not need to be a very large area). CAUTION: Scrape in a direction away from your hand to avoid cutting yourself.

The shell of a clam is made up of three layers: the homy outer layer, the thick, middle layer called the prismatic layer, and the innermost layer called the pearly layer. Carefully apply one drop of acid on the exposed prismatic layer. CAUTION: Do not let any acid contact your skin. The bubbling of the acid indicates that calcium carbonate (CaCO3) is present. Carefully rinse the shell with water once you have made your observations.

Skills Assessment: 3 pts. Verify your results of applying acid to the shell with your teacher.

Describe a situation where what you observed might actually be applied to the clam in its natural environment.

Name the material (chemical) that makes up the clam shell and give its chemical formula. (The "3s" are subscript even though formatting doesn't show it.)

How many layers make up the "shell" of the clam?

How many layers make up the "mantle" of the clam?

The mantle of the clam shell is what forms pearls.

A pearl is formed as a reaction to a foreign particle between the shell and mantle.

The white part of the clam shell that you applied acid to is called the periostracum.

The nacreous layer is better known by its common name, "mother of pearl".

Lets stop for a moment and look at some of the living clam's anatomy. The diagrams below show how the clam looks when healthy and alive. The foot and siphons are extended. Yours will not-look exactly like this because it is dead and these appendages have been retracted into the shell.
**Put on a pair of safety glasses during the process of opening the mussel.

Internal Anatomy of the Clam:
Your clam should be slightly gapped open. There might even be a piece of wood wedged between the valves (this guarantees the preservative gets inside the shell halves). First try to pry it open with your hands. If this will not work, use a screwdriver or other solid object to very gently pry the valves apart. Your clam should look like the one shown below in pane A. Look at the partially opened shell. Observe the anterior adductor muscle, posterior adductor muscle, mantle, siphon, gills, and foot. The opening between the two shells is called the gape.
OPENING the clam. Use above figure, pane B to assist you. Carefully insert the scalpel between the mantle and the left valve of the shell. Cut the anterior adductor muscle as close to the shell as possible. CAUTION: The scalpel is a sharp instrument. Always be very careful when handling it and cut away from your hand and body. Repeat this procedure to cut the posterior adductor muscle. Open the shell. If necessary, carefully run your fingers or scalpel between the shell and the mantle to separate the mantle from the shell. The space between the two halves of the mantle is the "mantle cavity." Open the left valve as far as possible. When done, your specimen should look like the diagram below.
Observe the hinge. Notice the interlocking teeth that hold the two valves of the shell together. Locate the "scars" from the anterior and posterior adductor muscles on the inner surface of the left valve. These scars indicate where the posterior and anterior adductor muscles were attached.

Locate the mantle, a thin layer of tissue that covers the visceral mass and foot. The visceral mass is a soft mass of tissue located dorsal to the foot. The mantle is usually cream or yellow in color with a brownish edge in a preserved clam. Locate the incurrent siphon and excurrent siphon. The siphons are folds in the mantle at the posterior of the clam. The incurrent siphon is ventral to the excurrent siphon. The incurrent siphon takes in water that contains oxygen and microscopic food particles. Water and waste materials are removed from the mantle cavity through the excurrent siphon. Examine these structures with a hand lens.

Skills Assessment Identification 10 pts: Identify the following structures for your teacher after you have located them on your specimen:

Left Valve: 1) posterior adductor muscle scar, 2) anterior adductor muscle scar, 3) cardinal teeth along hinge, 4) pallial line;
Right Valve: 5) posterior adductor muscle, 6) anterior adductor muscle, 7) mantle, 8) foot, 9) gills, 10) exhalant & inhalant siphons;

If the mantle wasn't already torn away when you opened the clam, use a pair of scissors and carefully cut away a portion of the mantle as shown in the figure below. With the mantle removed you can now observe the gills, folds of tissue covered with microscopic cilia. Gills are found in pairs, one on each side of the visceral mass. Use a probe and a hand lens to examine the gills. Observe the muscular, hatchetshaped foot located anterior and ventral to the gills. Locate the palps, a pair of leaflike structures ventral to the anterior adductor muscle and anterior to the gills. The mouth is a slit located between the palps, Water from the incurrent siphon passes over the gills toward the palps. Mucus and cilia on the palps trap food and direct it toward the mouth. Water then circulates out of the mantle cavity through the excurrent siphon.

Skills Assessment 2 pts: Show your teacher the following after you have located them on your specimen:
palps and mouth

The two main functions of the gills are 1) respiration, exchange of gases; and 2) catches food particles and brings them into the mouth of the clam.

Locate the visceral mass. In order to study the visceral mass in detail, remove the gills and set them aside in your dissecting tray.

Then use a pair of scissors to cut off the ventral portion of the foot as shown in the diagram below. With a scalpel or scissors, carefully cut the remaining portion of the foot into right and left sides.
The nervous system is composed of three pairs of ganglia (located anteriorly, posteriorly, and in the foot), all connected by nerves. The clam does not have a brain. A ganglion contains a limited number of neurons, whereas a brain is a large collection of neutrons in a definite head region.

Now it is time to explore. Some of the organs will be easy to find on your specimen and some of them will be very difficult. It depends on the quality of your specimen and the skill you impart. See what you can find. Figure 15-5 is reposted below to help you.

With the foot removed, locate the following structures:
1) reproductive organs (gonad), a spongy reddish mass
2) the saclike stomach near the mouth
3) the digestive gland, a light green mass surrounding the stomach
4) the coiled intestine leading from the stomach to the anus near the excurrent siphon
5) the pericardial cavity, an area between the visceral mass and the hinge
6) the heart contained within the pericardial cavity (the heart pumps blood into the aortas, which deliver it to blood sinuses in the tissues)
7) the kidneys, spongy brownish organs below the pericardial cavity
8) anus, discharges into the excurrent siphon

Skills Assessment 10 pts: After you have identified as many of the internal structures as you can, demonstrate your knowledge and show them to your teacher. (gonad, stomach, digestive gland, intestine, heart cavity, heart, kidney, anus)

As water goes through the clam's body it brings in food and oxygen.

As the water goes through the clam's body, it takes out carbon dioxide and waste.

Clams have an closed circulatory system. This means that they have vessels and arteries that carry blood to all the tissues inside the valves just like humans.

Reproduction: Most mussels and clams are male or female; a few species are hermaphroditic. The reproductive cycle in these organisms is quite interesting in that the juvenile stage is parasitic on fish. The eggs are released into the cavity of the gills where fertilization takes place. Each zygote then develops into a larva, called a glochidium. The larvae stay within the fish gills through the winter and are released into the water the following spring. If they come into contact with a fish, a contact stimulus causes them to close their valves and thus become attached to the gills or the fins of the fish host. The tissue of the fish reacts by growing around the larva. After several weeks, the parasitic larval form is released and begins a free-living existence.

Give two advantages of the larval stage of the clam being attached to the gills or fins of a fish?

Continue Lab #15 Animal Diversity by going to Part 2: Squid