• Describe the appearance of various organs found in a crayfish.
• Name the organs that make up systems of the crayfish.
• safety goggles, gloves, magnifying glass, a lab apron, plastic zip lock bag preserved crayfish, pen, dissecting tray, paper towels, scissors, forceps, dissecting needle, and dissecting pins.
In this lab, you will observe the external structures of a crayfish and dissect it to study its internal structures and systems.
Like all crustaceans, a crayfish has a fairly hard exoskeleton that covers its body. As shown in the diagram on the next page, its body is divided into two main parts, the cephalothorax and the abdomen. The cephalothorax consists of the cephalic (or head) region and the thoracic region. The part of the exoskeleton that covers the cephalothorax is called the carapace. The abdomen is located behind the cephalothorax and consists of six clearly divided segments. The cephalothorax consists of 13 segments. Each segment of both the cephalothorax and the abdomen contains a pair of appendages. The head (or cephalic) region has five pairs of appendages. The antennules are organs of balance, touch, and taste. Long antennae are organs for touch, taste, and smell. The mandibles, or jaws, crush food by moving from side to side. Two pairs of maxillae hold solid food, tear it, and pass it to the mouth. The second pair of maxillae also helps to draw water over the gills. Of the eight pairs of appendages on the cephalothorax, the first three are maxillipeds, which hold food during eating. The chelipeds are the large claws that the crayfish uses for defense and to capture prey. Each of the four remaining segments contains a pair of walking legs. In the abdomen, the first five segments each have a pair of swimmerets, which create water currents and function in reproduction. The sixth segment contains a modified pair of uropods. In the middle of the uropods is a structure called the telson, which bears the anus. The uropod and telson together make up the tail fan. The crayfish moves backward by forcing water forward with its tail fan.
Procedure Part 1—External Anatomy of a Crayfish
1. Put on safety goggles, gloves, and a lab apron.
2. Place a crayfish on its side in a dissection tray. Use the diagram below to locate the cephalothorax and the abdomen. The carapace, a shield of chitin, covers the dorsal surface of the cephalothorax. On the carapace, observe an indentation, the cervical groove, that extends across the midregion and separates the head and thoracic regions. On the thoracic region, locate the prominent suture or indentation on the cephalothorax that defines a central area separate from the sides. Note the individual segments of the abdomen.
What is the main difference between the cephalothorax and abdomen?
3. Turn the crayfish with its DORSAL side upward, and locate the rostrum, which is the pointed extension of the carapace at the head of the animal shown in the diagram above. Beneath the rostrum locate the two eyes. Notice that each eye is at the end of a stalk.
4. Locate the five pairs of appendages on the head region. First locate the antennules in the most anterior segment. Behind them observe the much longer pair of antennae.
Why is it useful to view the specimen on its Dorsal side for this part of your study?
5. Locate the mouth. Then observe the mandibles, or true jaws, behind the antennae. Now locate the two pairs of maxillae, which are the last appendages in the cephalic region.
Which appendages in the cephalic region are related to the eating of food?
6. On the thoracic portion of the cephalothorax, observe the three pointed maxillipeds.
How are the maxillipeds related to eating?
7. Next observe the largest prominent pair of appendages, the chelipeds, or claws. Behind the chelipeds locate the four pairs of walking legs, one pair on each segment.
8. Now use the walking legs to determine the sex of your specimen. Locate the base segment of each pair of walking legs. The base segment is where the leg attaches to the body. Use a magnifying glass to study the inside surface of the base segment of the third pair of walking legs. If you observe a crescent-shaped slit, you have located a genital pore of a female. In a male, the sperm duct openings are on the base segment of the fourth pair of walking legs. Use a magnifying glass to observe the opening of a genital pore.
Is your specimen a male or a female?
Exchange your specimen with a nearby classmate who has a crayfish of the opposite sex. Then study its genital pores.
9. On the abdomen, observe the six distinct segments. On each of the first five segments, observe a pair of swimmerets.
10. On the last abdominal segment, observe a pair of pointed appendages modified into a pair of uropods. In the middle of the uropods, locate the triangular-shaped telson.
11. Now turn the crayfish ventral side up. Observe the location of each pair of appendages from the ventral side.
From which view, dorsal or ventral, can you see the location of the appendages on the segments more clearly?
12. Remove all jointed appendages of the crayfish and attach them to the table on the crayfish worksheet.
If dissection is two day, complete steps 13 and 14 only!
13. Next you will study the internal anatomy of a crayfish. If you must store your specimen until the next lab period, cover it with a dampened paper towel. Then place the specimen on the tray in a plastic bag. Close the bag with a twist tie. Write your name on the bag with a felt-tip marking pen, and give your specimen to your teacher.
14. Clean up your work area and wash your hands before leaving the lab.
Part 2—Internal Anatomy of a Crayfish
15. Put on a lab apron, gloves, and safety goggles.
16. Using one hand to hold the crayfish dorsal side up in the dissecting tray, use scissors to carefully cut through the back of the carapace along dissection cut line 1, as shown in the diagram below. Cut along the indentations that separate the thoracic portion of the carapace into three regions. Start the cut at the posterior edges of the carapace, and extend it along both sides in the cephalic region.
17. Use forceps to carefully lift away the carapace. Be careful not to pull the carapace away too quickly. Such action would disturb or tear the underlying structures.
18. Place the specimen on its side, with the head facing left, as shown in the diagram below. Using scissors, start cutting at the base of cut line 1. Cut along the side of the crayfish, as illustrated by cut line 2. Extend the cut line forward toward the rostrum (at the top of the head).
19. Use forceps to carefully lift away the remaining parts of the carapace, exposing the underlying gills and other organs.
20. Use the diagram below to locate and identify the organs of the digestive system. Locate the maxillae that pass the pieces of food into the mouth. The food travels down the short esophagus into the stomach. Locate the digestive gland, which produces digestive substances and from which the absorption of nutrients occurs. Undigested material passes into the intestine. Observe that the intestine is attached to the lobed stomach. The undigested material is eliminated from the anus.
Rows of chitinous teeth line the stomach. Predict their function.
21. Use the diagram below to locate and identify the organs of the respiratory system. Locate the gills, which are featherlike structures found underneath the carapace and attached to the chelipeds and walking legs. A constant flow of blood to the gills releases carbon dioxide and picks up oxygen.
The feathery nature of the gills gives them a very large surface area. Why is this important?
22. Use the diagram of the internal anatomy of the crayfish to locate and identify the organs of the circulatory system. Locate the dorsal tubular heart and several arteries. The crayfish has an open circulatory system in which the blood flows from arteries into sinuses, or spaces, in tissues. The blood flows over the gills before returning to the heart.
23. Use the same diagram to locate and identify the organs of the nervous system. Find the ventral nerve cord. Locate a ganglion, one of the enlargements of the ventral nerve cord. Locate the dorsal brain, which is located just behind the compound eyes. Note the two large nerves that lead from the brain, around the esophagus, and join the ventral nerve cord.
Many nerves leave from each ganglion. Where do you think these nerves go?
24. Use the same diagram to locate and identify the organs of the excretory system. The blood carries cellular wastes to the disk-like green glands. Locate these organs just in front of the stomach. The green glands excrete waste through pores at the base of each antenna.
What organs in your body carry out the same function as the green glands?
25. Use the diagram once again to locate and identify the organs of the reproductive system. The animal shown in the diagram is a male crayfish. If your specimen is a male, locate the testis. The testis is the long, white organ under the heart and a bit forward. The sperm ducts that carry sperm from the testis open at the fifth walking leg. If your specimen is a female, locate the bi-lobed ovary. It is in the same relative position as the testis, but the ovary appears as a large, reddish mass under the heart. Then locate the short oviducts that extend from near the center of each side of the ovary and open at the third walking leg. Exchange your specimen with a nearby classmate who has a crayfish of the opposite sex. Then study its reproductive system.
25. Dispose of your materials according to the directions from your teacher.
26. Clean up your work area and wash your hands before leaving lab.
All chordates have a notochord, dorsal nerve cord, pharyngeal pouches, & postanal tail at some time in their life
Notochord is a firm, flexible rod of tissue located on the dorsal side of the body that becomes part of the endoskeleton in vertebrates
Dorsal nerve cord is a hollow tube lying dorsal to the notochord that becomes the brain & spinal cord in vertebrates
Pharyngeal pouches are small outpockets of the anterior part of the digestive tract that become gills in aquatic chordates & jaws, inner ear, & tonsils in terrestrial chordates
Postanal tail consists of muscle tissue & lies behind the posterior opening of the digestive tract
Subphyla of Chordates
The Phylum Chordata includes all of the vertebrates, as well as two groups of marine animals that lack backbones and are called invertebrate chordates
The phylum is divided into three subphyla, determined by the development of the notochord
Subphylum Cephalochordata contains about 24 species of blade-shaped animals known as lancelates that retain the notochord, dorsal nerve chord, pharyngeal pouches, and postanal tail throughout their life
Subphylum Urochordata contains 2,000 species commonly called tunicates because their bodies are covered by a tough covering, or tunic
* Called sea squirts because they shoot out a stream of water when touched
*Sessile, barrel-shaped, filter feeding animals that live on the sea bottom
*Adults have a pouch-like pharynx with slits
*Adults do not have a notochord, dorsal nerve cord, or postanal tail
Subphylum Vertebrata is the largest subphylum in which the notochord is replaced with vertebrae
* Skeletons consist of bone &/or cartilage
* Brain is protected by a cranium
* Well developed 4 chambered heart with a closed circulatory system
* Includes fish, amphibians, reptiles, birds, & mammals
Have a head & segmented trunk with one pair of legs on each segment
Breathe through gills
Single pair of antenna
Includes 2 classes — Xiphosura (horseshoe crab) and Arachnida (spiders, ticks, scorpions, & mites)
Have a cephalothorax (fused head& thorax) and abdomen
Simple eyes or ocelli
Have 6 pairs of jointed appendages:
* Chelicerae – claws or fangs (1 pair)
* Pedipalps – used for feeding, walking, sensing, transferring sperm (1 pair)
* Walking legs – movement (4 pairs)
* Not true crabs
* Fanglike pincers or chelicerae
* Use book gills to breathe
* Eight legs
* Chelicerae or fangs with venom
* No antenna
* Breathe by book lungs &/or tracheal tubes
* Arachnid that feeds on insects (carnivores)
* Have oval shaped, unsegmented abdomen
* Cephalothorax connected by narrow waist to abdomen
* Have 8 simple eyes or ocelli
* Fangs pierce prey, inject poison, & suck out body fluids
* Pedipalps on head help sense prey & move it to the mouth
* Open circulatory system
* Ostia are openings in heart where blood reenters
* Body cavity called hemocoel
* Hemocycanin is oxygen-carrying pigment in blood
* Have silk glands to make silk & spinnerets to release silk for webs
* Breathe by book lungs & tracheal tubes
* Malpighian tubules filter wastes & reabsorb water
Ticks & Mites
* Parasitic arachnid
* Fused cephalothorax & abdomen
* Most abundant arachnid
* Need blood meal to molt
* Mites can damage fruit & feed on dead skin at base of hair follicle
* Ticks carry Lyme disease & Rocky Mountain Spotted Fever
* Have a cephalothorax & long segmented abdomen curled over body
* Prefer dry regions
* Poisonous stinger on end of abdomen
* Breathe through book lungs
* Pedipalps modified into claws
* Nocturnal predators
Marine members include shrimp, lobster, copepods, barnacles, & crabs
Terrestrial crustaceans called isopods include pillbugs & sowbugs
Freshwater members include crayfish & Daphnia (water fleas)
All have jaws are mandibles for chewing or tearing
Known as mandibulates
Have cephalothorax & abdomen
Have 10 pairs of jointed appendages
Breathe through gills
* Sessile crustaceans that live in limestone case
* Filter plankton with 12 appendages called cirri
Isopods (pillbugs & sowbugs)
* Live on land in dark places
* Have 7 pairs of legs on a segmented body
* Can roll into a ball for protection
* Cephalothorax made of 13 fused segments & covered by protective carapace
* Antennules located on head help in balance, touch, & taste
* Statocysts – balancing organs at the base of antennules
* Antenna on head used for touch & taste
* Maxillae – paired mouthparts that move side to side to tear food
* Maxillipeds – help hold food
* Chelipeds – claws used to capture food & for protection
* Mandibles – jaws that move up & down to crush food
* Walking legs – 8 pairs used for movement
* Swimmerets – under abdomen to swim, gas exchange, & protect eggs/young
* Abdomen ends in flat segment called telson with flat uropods on each side
* Compound eyes on stalks
* Chitinous teeth in stomach grind food
* Wastes leave through anus
* Green glands filter wastes from blood & help with salt balance
* Open circulatory system with heart to pump blood to gills & body cells
* Ostia – one way valves allowing blood from dorsal sinus to reenter heart
* Gills attached to walking legs
* Separate sexes that mate in fall & sperm stored in seminal receptacle
* Eggs attach to swimmerets of female & hatch in several weeks
* Largest group of crustaceans
* Make up most of the marine plankton
* Serve as food for many marine animals
* Found in freshwater, marine, & moist terrestrial environments
All have antenna, mandibles (jaws), & unbranched appendages
Includes 3 classes — Chilopoda (centipedes), Diplopoda (millipedes), & Insecta
Known as myriapods
Most are terrestrial
Exoskeleton prevents desiccation (water loss)
Flattened body with longer legs for fast movement
Have 1 pair of legs per body segment
Mandibles & maxilla for chewing prey (insects & earthworms)
Claw-like appendages or pincers on 1st body segment that can inject venom
Can coil up for defense
Have 2 pairs of legs per body segment
Scavengers on decaying vegetation as they burrow through soil
Roll into ball when threatened & spray noxious chemical containing cyanide
Since sponges look like plants, it is understandable why early biologists thought they were plants. Today, we know that sponges are simple, multicellular animals in the Kingdom Animalia, Phylum Porifera. This phylum is thought to represent the transition from unicellular animals to multicellular animals. Most (but not all) sponges are asymmetrical and have no definite shape. Sponges, like all animals, are eukaryotic – meaning their cells have a nucleus. Porifera in Latin means “pore-bearer” and refers to the many pores or openings in these animals. Because of these pores, a sponge can soak up and release water. At one time, real sponges were used for cleaning and bathing. Today, most are artificially made.
All adult sponges are sessile, meaning they are attached to some surface. Since they cannot move, sponges cannot pursue their food. Instead, they are filter feeders, meaning they obtain their food by straining the water for small bits of food like bacteria, algae or protozoans.
Sponges exhibit less specialization (adaptation of a cell for a particular function) of cells than most invertebrates. The primitive structure of a sponge consists of only two layers of cells separated by a non-living jelly like substance. The outer layer of the sponge is the epidermis which is made of flat cells called epithelial cells. Color all the epithelial cells (B) of the epidermis peach or pink.
The inner layer consists of collar cells (A) whose function is to circulate water through the sponge. They do this by swishing their flagella which pulls water through the incurrent pore – water then travels out the osculum at the top of the sponge. As water passes through the sponge in this way, cells absorb food and oxygen and waste is excreted. Color the osculum (D) dark blue, the incurrent pores (C) light blue. Color the inside of the sponge where water circulates the same light blue as you colored the incurrent pores. Color all the collar cells (A) red.
In the jelly-like substance between the epidermis and the collar cells are cells called amebocytes – because they look like amebas. The job of the amebocytes is to travel around distributing food and oxygen to the cells of the epidermis. Because of the amebocytes, scientists believe that sponges evolved from protists. Color all of the amebocytes (E) green – look for them carefully.
The body of the sponge would collapse if it did not have some type of supporting structure. Some sponges have a soft network of protein fibers called spongin. Others have tiny, hard particles called spicules. Many of these spicules also stick out of the epidermis and provide the sponge with protection. Most sponges have a combination of spicules and spongin, the ratio often determines how soft or hard the sponge is. Search for and color all the pointy spicules (F) brown.
Reproduction for sponges can be accomplished both sexually and asexually. There are three ways for a sponge to reproduce asexually: budding, gemmules, and regeneration. Sponges can simply reproduce by budding, where a new sponge grows from older ones and eventually break off. Color the adult sponge (J) pink and all the buds (G) you can find red. Sponges can also reproduce by regeneration, where missing body parts are regrown. People who harvest sponges often take advantage of this by breaking off pieces of their catch and throwing them back in the water, to be harvested later. Finally, sponges can reproduce by creating gemmules – which is a group of amebocytes covered by a hard outer covering. Color the gemmule (H) yellow.
Sexual reproduction occurs when one sponge releases sperm into the water. This sperm travels to another sponge and fertilizes its eggs. The larva form will then swim to another location using its flagella where it will grow into an adult sponge. Most sponge species are hermaphrodites, they can produce both eggs and sperm.
1. What did early biologists think sponges were? ______________________
2. Sponges belong to the Kingdom _________________ and the Phylum _______________
3. Sponges are [ unicellular or multicelluar ] and [ prokaryotic or eukaryotic ]
4. What type of symmetry do sponges have? ___________________________________
5. What does it mean to be sessile? ____________________________________
6. How do sponges get their food? ___________________________________
7. Water enters the sponge through the _____________________ and leaves through the
8. What is the job of the amebocyte? ________________________________________
9. What two substances give the sponge support? _________________________________
10. Tiny sponges growing from the main body of the sponge are called _________________
11. What is a gemmule? ___________________________________________________
12. What is a hermaphrodite? ______________________________________________