Biology Crayfish Dissection My daughter (Rachel) and I put together this presentation a few years back. We will use this to help you get ready for the crayfish dissection.
Kingdom: Animalia Phylum: Arthropod Class: Crustacea The Crayfish These cool little critters live in freshwater habitats (lakes, streams etc.). These creatures are generally nocturnal (night) scavengers. Crayfish have been used as food and have a mild lobster taste.
The Crayfish is a Crustacean. They are relatives to crabs, shrimps, lobsters, and barnacles. All crustaceans have exoskeletons. Crustaceans have antennae, two or three body segments, they also have chewing mouth called mandibles.
Objectives: • 1. Understand all major crayfish systems for maintaining homeostasis. • 2. Correctly dissect a crayfish and accurately identify various crayfish organs and systems. • Understand how the crayfish fits into the world. • Master (85%) both the dissection quiz (in class) and the online guide quiz (UTIPS).
All living things must maintain a relatively stable internal environment to survive. The term used to describe this is "homeostasis." Living things carry out different essential functions in order to accomplish this task. Multicellular organisms have “systems” that work together to maintain this stable environment. For example when you run your body is placed under sever stress. Various systems will start to work overtime keeping your body alive. Your heart starts beating faster and your breathing increases. Your body is trying to deliver oxygen and take away carbon dioxide (respiratory waste) form working muscles etc. Your skin starts to sweat reducing the excess body heat created by the activity. Without your body systems working together your systems will fail and death would ensue. There are many more system accommodations that occur as you run or engage your body in different activities. Multicellular organisms maintain homeostasis differently. Compare the differences between warmblooded and cold blooded organisms. To adjust body temperature insects or reptiles will move their body to a location that will ether warm or cool their body depending on their needs. Below are a few examples of various systems found in multicellular organisms. Digestive /Feeding Response /Nervous Movement Circulatory Respiratory Reproductive Excretion Single celled organisms do not have systems because they are only made of one cell. Thus each cell must carry out all of these functions without relying on tissues, organs and organ systems (ex. bacteria, yeast, and most protists). See your text book and dissection guide to research how crustaceans carry out all the needs to the left. They will not be discussed in this presentation.
For the remainder of the presentation you will learn the external and internal parts of the crayfish. PAY CLOSE ATTENTION TO THE POINTER. Lets start with the overall body plan of the crayfish.
Anterior Dorsal Surface Posterior Ventral surface bottom
The probe is underneath claspers. The claspers are used by males to hole onto females. These structures are not present in females.
Rostrum: is like the “nose" of the crayfish. The eyes are found laterally on both sides.
The two structures I am pointing to are called antennules. The larger structure we are holding (bottom left) is the antennae. The antennae is much larger than the antennules. Both are used to sense their environment.
The crayfish has two main body sections. The cephalothorax and abdomen. The cephalothorax is a fused head and thorax. I am pointing to this structure. Cephalothorax
These big pinchers are called chelipeds, they are used for feeding and to fight off predators.
These are called swimmerets and they help the crayfish swim, they also help the female holding the eggs.
To see inside the abdomen we are going to take some surgical scissors and cut laterally going from the telson towards the head.
Pulling the top part of the abdomen to the side will show the two different muscles. Can you see the extensor muscle? This is the extensor muscle.
The flexor muscle is large and is what people eat. When contracted the flexor muscle causes the abdomen to flip down and forward. This causes the little bugger to swim in a backward motion.
Just underneath the flexor muscle is the ventral nerve cord. It is hard to see but the pointer is just underneath it.
To make things more interesting lets remove the carapace. To do that we will cut from the bottom side just behind the eyes and continue all the way across to the opposite side.
We will then remove the top part of the cephalothorax. This is called the Carapace. The function of this piece of exoskeleton is to protect internal organs.
Check out these gills. The crayfish uses them to take in oxygen and give off carbon dioxide. Gills
Crayfish have mandibles that chew the food into little pieces before sending it to the stomach.
While in the stomach the food is further ground by these little hard like teeth.
Looking inside the stomach shows the Gastric Mill. The little tooth-like structures continue to grind up the food before it is sent into the intestine and out the anus.
After removing the stomach we can see the digestive gland. This structure releases enzymes to help breakdown food.
Just behind the digestive gland is the heart. The pointer is in one of the openings.
When the stomach is removed two nerve cords can be seen. These are the nerve cords connected to the brain and also extend backwards fusing into the ventral nerve cord.
Looking towards the head you can see white stuff what scientist call the brain or ganglia.
This is the green gland. It is used to extract cellular waste from the crayfish. We use our kidneys.