For YOUR JOURNAL, this week, we are expecting the following.
Photographs of external and internal shrimp anatomy.
Movie showing beating heart and if at all possible following one artery away from the heart until it ends.
Movie of barnacle feeding.
Movie of model crustacean moving. This is an important movie. It will serve as your model that you use next week for comparative locomotory studies in crustaceans.
If specimens are available, photographs of barnacle larvae and skeletal shrimp external anatomy. Movies of skeletal shrimp feeding and moving. Today we will try to begin to build a picture of the “typical” arthropod. In some sense such a creature does not exist, yet all arthropods do share several features in common.
We will be using as the grass shrimp as our model. This species is relatively large and transparent, so that most of its organs can be seen using the stereo-scope. You may try feeding it some fish food. Just use a pinch so water does not become contaminated. For a side view, try giving it a small rock or piece of vegetation to hang on to. Often you can tilt the vegetation for a better view of side view of some important organs such as the bill.
External anatomy. Try to identify the different segments of the body, cephalothorax (carapace), and abdomen. Try to count the number of abdominal segments, legs, and walking legs. Do they match the number in the picture below which is a diagram of a large commercial fish cultivating for food. RECORD YOUR OBSERVATIONS IN YOUR JOURNAL
Internal anatomy: Below is a diagram of a female crayfish.
The reproductive organs of the male appear as smaller but similar sac like structures. You will probably be able to easily distinguish the heart, gills (need sideview), stomach and intestine. Feed you animal some colored fish food and if it is cooperative, you should be able to trace the movement of the food down the digestive track. Can you describe how the mouth parts move while the shrimp is feeding?
Gills are located just below the heart.
Open circulatory system. Take a short video of the beating heart. Can you trace the flow of hemolymph out of the heart into the major arteries? RECORD YOUR OBSERVATIONS IN YOUR JOURNAL. Below are some diagrams to help you.
The first is of a lobster. Crayfish and shrimp are smaller and to not have veins. It is a very good diagram of the relationship of the gills to the major vessels and heart.
Diagram of heart showing relative placement of ostia in shrimp and crayfish.
You should try following the anterior median artery since it will not be as obscured by other organs as the dorsal artery.
You probably will not be able to see ostia in these small shrimp, but check out the movie below of a dissection in a large crayfish that shows the ostia closing and opening. http://www2.gsu.edu/~bioasx/heartbeat.html
2. Barnacles We have the purple striped barnacle, Balanus amphitrite and an unidentified species (probably another species of Balanus). Sometimes keeping these overnight in dishes in the dark will produce larvae, but don’t spend a lot of time looking for them. Some years the dishes are full of them, in others we don’t see any. I always order barnacles for this first lab so you have enough time to watch and film them.
Examine the diagram below of a barnacle. The barnacle feeds with its legs.
a. You are to film and describe feeding in a barnacle.
Obtain a dish of barnacles or if all are in one dish simply gently scoot a barnacle or two into a smaller container. Make sure the smaller container can hold enough water to cover the barnacle. While you are waiting for the animal to adjust to its new surroundings, document any animals that are using the barnacle as habitat. Those students obtaining the dish containing the larger colony should share their observations with the class. In a large colony, you should be able to see most of the major groups of animals we have been discussing in lecture.
Good reference for barnacle behavior. http://creaturecast.org/archives/490-mating-when-you-are-stuck-to-a-rock
(Hint: Patience is the key here to good filming.
Focus and adjust your lighting using the empty container that will house your barnacle. Place your barnacle under the stereoscope, lights off and wait for it to become adjusted to its new surroundings. If you barnacle does not feed after it is set and left alone in its new container for a few minutes, you can try feeding it macro zooplankton or if that does not work phytoplankton. Simply use a small pipette to obtain some food to add to your dish containing the barnacle. Is there evidence of mating? If so, please film mating in these animals.
b. Types of barnacle larvae. The diagram below shows the Cyprid larvae attaching to the substrate to assume the sessile lifestyle of the adult.
b. If larvae are produced during the night, they will be visible as small objects darting around in these dishes. Use a small pipette to obtain some of these if you see them, place in the smallest dish available, and observe how they move under the stereoscope. Identify if they are nauplius or cyprid larvae. Record your observations, obtaining photographs whenever possible.
3. Check with your instructor if marine Caprellid or skeleton shrimp survived the night. These are truly spectacular creatures to watch feed and move. a. If so, please obtain a film of their l feeding behavior. b. You should also be able to obtain photographs of overall structure to label. Label antennae and peropods at least in photographs. If not, we will try to order these again.
4. You are to obtain a movie of model locomotion in two crustaceans. These movies will serve as the model to which you will compare locomotion in a variety of crustaceans, so you want to make sure that you can clearly see how the legs or other appendages are used in locomotion. You can use your movie of Caprellids if you wish. Then simply watch locomotion in the glass shrimp or sexy shrimp in the tank. All these species are large it is very easy to see how the appendages move. If the Caprellidsdid not survive the trip, I have also ordered cultures of some fresh water forms. Your instructor will give you more instructions on how to work with these. Unfortunately we move quickly from the large Caprellids and shrimp to species that need to be examined under the stereoscope. Their size and quickness will provide a bit of a challenge for good observation of how appendages are used.
5 We also ordered, sacculina, Loxothylacus texanus, a degenerate parasitic barnacle that attacks crabs, Callinectes sapidus, sending branching roots throughout their bodies. This species also alters sexual characters and prevents molting in the crab. A well developed parasite actually mimics in position and overall appearance the egg mass normally carried ventrally by females. The parasite will feminize male and female crabs. Crabs nurture the “eggs” as if they were their own eggs. Crabs will even wave their arms and perform other spawning behavior causing the parasitic larvae to be released. Larvae are typical nauplii and are free living.