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Dissection of a Turtle: Phylum Chordata (Class Reptilian)

Introduction

Turtle, of the Order Chelonii or Testudines, are the only reptile that has a shell and no teeth. Turtles are found in many parts of the world with temperate or tropical climates. Some kinds live on land, others in fresh water or salt water. Land turtles can swim, and water turtles breathe air and lay their eggs on land. Turtles are probably the longest-living group of animals, some living 150 years or more. Full-grown turtles vary in size from certain American freshwater turtles 3 1/2 inches (9 cm) long and less than one pound (.45 kg) in weight to sea-living leatherback turtles 8 to 9 feet (2.4 to 2.7 m) long and weighing up to 1,500 pounds (680 kg). Most species of turtles grow throughout life, although slowly after the first 5 to 10 years.

In the United States, all shelled reptiles are called turtles. Some land turtles are also called tortoises, and various edible freshwater turtles are known as terrapins. In England, shelled reptiles are called tortoises, except for a few marine species that are known as turtles. Turtles have been in existence for about 200,000,000 years. They are the oldest reptile group that has living representatives.

Many species of turtles are in danger of extinction due to human activities. Turtles are captured for food and other uses; their habitats and nesting sites are being destroyed by pollution, the drainage of wetlands, and commercial development; and they are accidentally caught in fishing nets. The endangered sea turtles include the hawksbill, Atlantic ridley, and leatherback; certain populations of the green and Pacific ridley sea turtles are also endangered. Endangered land turtles include the Bolson and giant Galápagos tortoises. Endangered freshwater turtles include various softshell, slider, and cooter species.

Since turtles are cold-blooded, they cannot live in places that are cold all year long. But turtles live almost everywhere else. They live in hot, sandy deserts. They live in lush, green forests and grasslands. Some turtles live high in the mountains. Others live in wet, lowland marshes and swamps. Besides living on land, turtles also live in water. Many kinds of turtles live in fresh water, such as in lakes, ponds, or rivers. Sea turtles live in salty oceans.

A turtle's shell structure consists of two separate pieces—an upper shell and a bottom shell—joined at the sides by a bony bridge. The upper shell, called the carapace, may be highly domed, low and rounded, or flattish on top with steep sides. The bottom shell, or plastron, is flat or slightly concave. In most turtles the two shells are each composed of an inner layer of bone fused to the ribs and other bony structures of the animal's body, and an outer layer of horn. Both layers are made up of sections that fit together like pieces of a mosaic. However, the sections of the two layers do not coincide. One species of sea turtle has a leathery covering of skin instead of horn over the bony layer.

Most kinds of turtles can pull their head, legs, and tail into their shell, which serves as a suit of armor. Few other animals with a backbone have such natural protection. The shell covering the back of a box turtle is round. This makes a box turtle look a little like a stocky lizard carrying an upside-down salad bowl on its back. The box turtle’s shell is covered in horny plates that fit together in a geometric pattern something like a quilt. Box turtles are different from many other turtles because they have a hinge on the bottom of their shell. They can pull their legs, head, and tail into their shell and then use this hinge to close up and “box” themselves inside. Box turtles

are small pond and marsh turtles that live in North America. They are called box turtles with good reason. If an enemy such as a rat comes near one of these turtles, it can “box” itself up inside its shell. No other turtles have shells quite like these land-dwellers. A box turtle’s plastron is hinged. This lets the turtle bring the plastron right up against the carapace. Once the box turtle tucks itself in, it can close its shell up tight.

Turtles cannot expand and contract their lungs by rib movements, because the ribs are held rigid by fusion with the shell. Muscles in the turtle's limbs contract and enlarge the lung capacity, drawing in air. Abdominal muscles contract and force the lungs to expel air. In some turtles a pumping action of throat muscles aids in breathing. Some aquatic turtles also respire by getting a little oxygen from water through the mucous membranes.

The head, limbs, and tail of the turtle protrude from the shell, but—in most species—can be drawn inside the shell for protection. Some turtles can move hinged parts of the shell to enclose the softer parts of their bodies completely. Most turtles have strong horn-covered jaws and beaks with which to tear their food into bits. Turtle skin is tough and often covered with scales. Freshwater turtles have webbed feet, and marine species have flippers.

The carapace may be rough or smooth, and the plastron is usually smooth. Carapaces vary in color from greenish brown to almost black. Plastrons are paler and often yellow. Turtles' shells may be marked with dark or light circular lines and with bright markings of red, orange, or yellow. The skin may be brightly marked also.

Method

Apparatii

Turtle Specimen: ie. Pseudemys

Magnifying Lens

Scissors

Fortified Scissors

Forceps

Blunt Probe

Scalpel

Fortified Scalpel

Gloves

Resources

Procedure: May need to refer to the “Directions and Planes in Anatomical Description Chart”

External Anatomy

1. Using a reference, locate the following external structures (bold): (see necessary Figures)

External Features: p2

Beak

Limbs

Carapace

Neck

Plastron

Bridge

Eyes

Tail

Scutes

Marginal Scutes

Claws

* Female urogenital structures: ie Cloaca (see p32; Figure 19); (may need to wait for internal dissection directions) Note: Females usually have a short tail while males have a longer tail.

* Male urogenital structures: ie Penis (see p33; Figure 20); (may need to wait for internal dissection directions) Note: Females usually have a short tail while males have a longer tail.

* Pending on which gender you have, find someone else in the class who has the opposite and note their anatomy

Oral Cavity: p14-15

2. Force open the turtle’s mouth and cut through the soft tissue of the jaws where they are joined together. Cut so you can open the mouth wide enough to see the beginning of the esophagus. Note: no teeth for this reptile. Refer to the Figure 10.

3. Using a reference, locate the following external structures (bold):

Internal (or External) Nares = Lead to the nasal cavity.

Pharynx = The back of the mouth or throat. Food, water and other nutrients are ingested into two main cavities in most turtles, the mouth and the pharynx. These two cavities are located inside of a turtles skull.

Esophageal Opening = Leads to the esophagus that leads down to the stomach.

Tongue = For mechanical digestion and taste.

Internal Dissection and Anatomy: p28-35; 45-48

4. Read the information from the manual provided to you. Remember, there may be more than one way to dissection the animal and that the manual simply provides a detailed way of doing the dissection.

5. Follow along in the manual in accordance to what is being asked of you to find. At some points, the manual may ask you to remove structures/organs. This is fine; however, do not through anything away unless you ask permission.

6. Be sure to read the information of each structures and/or organ. There may be information not discussed in class that is important or information that provides more detail to what was lectured upon.

Refer to Figures: 18-20, 25, 27-29

7. Using a scalpel, cut along the “bridge” and “surrounding muscle / legs” but close to the “plastron” while someone keeps pressure to separate the two shell halves.

Abdominal / Thoracic Systems:

8. Using a reference, locate the following external structures (bold):

Mesenteries = Thin connective tissue that helps hold organs in place.

Trachea = Tube that transport air to and from the lungs. Contains cartilage to prevent collapsing. The Glottis of the turtle is a small opening positioned behind the tongue that acts as a barrier between the pharynx and the larynx when swimming underwater, diving or eating. The larynx is connected to the glottis and leads to the trachea. It is considered to be the upper most portion of the respiratory duct.

Esophagus = Smooth muscular tube that transports food to the stomach via peristalsis.

Liver = Largest organ (gland) that primarily secretes bile to emulsify fats during digestion.

Gall Bladder = Stores bile make by the liver and found just below and behind the liver.

Lung = Lie directly underneath of the turtle's carapace (or upper shell portion) are big, sponge like organs which are also typically pink in color. Throughout the lungs the Bronchi break into smaller tube like structures called bronchioles. The bronchioles then continue the pattern, decreasing in size until they come to their end in what is called the alveolus (plural: alveoli). The alveoli are small groups of air sacs which is where the actual gas exchange takes place. The oxygen from the air dissolves into the blood and simultaneously the carbon dioxide diffuses out of the blood into the air.

Spleen = Used to help filter blood of old worn out blood cells.

Fat Bodies = Tissue that stores lipids for energy needed by the organism.

Pericardial Sac = Membrane that surrounds and protects the heart.

Heart = Three chambered, the heart consists of the Left Auricle, the Right Auricle and the Ventricle. The ventricle is somewhat separated by a partial septum which helps to minimize the mixing of deoxygenated and oxygenated blood.

Stomach = Powerful digestive enzymes and acids within the turtle's stomach decompose the food. The stomach also holds the food temporally prior to going into the small intestine.

Pancreas = Sliver like gland located next to the small intestine. It aids in the digestive process by introducing digestive enzymes into the small intestine as well.

Small Intestine = Connected from the stomach to the large intestine. Villi (or villus singular) located on the small intestine wall absorb food into the body.

Large Intestine (Colon) = Reabsorbs excess waste and water produced by the digestive system.

Cloaca = Where urine and waste leaves the body. Sperm (males) / eggs (females) leave from here too

Urogenital / Urinary Systems:

9. Using a reference, locate the following external structures (bold):

Female:

Urinary Bladder = Storage place of the urine. The Accessory Bladder (optional): In females, these organs are known to hold water to soften the ground while digging a nest.

Kidney(s) = Performs the blood filtering process and the wastes are then sent to the bladder as urine.

- dark lobed organs found on either side of the cloaca; below bladder (Fig 20 or 27

Ovaries = Primary reproductive organ; produces oocytes (pre-fertilized eggs). Located on either side of the bladder (see Fig 20)

Oviduct (may have Eggs) = Tube connecting ovaries with cloaca. Eggs produced in ovaries enter the oviducts. After mating, sperm from the male travel up the oviducts and fertilize the egg. The egg then continues down the oviduct into the cloaca.

Cloaca = Opens to the outside of the turtle's body. It receives waste products from the large intestine and bladder and sperm (male) or eggs (female).

Male:

Urinary Bladder = Storage place of the urine. The Accessory Bladder (optional) is known to hold extra water.

Kidney(s) = Performs the blood filtering process and the wastes are then sent to the bladder as urine.

- dark lobed organs found on either side of the cloaca; below bladder (Fig 20 or 27)

Testis (w/ an Epididymis on top of each) = Male reproductive organs that produces sperm. Located on either side of the bladder (see Fig 20)

Penis = Reproductive organ for males to help transfer sperm to a female.

Cloaca = Opens to the outside of the turtle's body. It receives waste products from the large intestine and bladder and sperm (male) or eggs (female).