Download Arthropods

FOR YOUR JOURNAL, this week, we are expecting the following.
1 and 2. Photographs of external and internal shrimp anatomy. Include in your journal
observation a list of internal structures you have located.
3. Movie showing beating heart and if at all possible, following one artery away from the heart
until it ends.
4. Movie of barnacle feeding (and mating if possible). If specimens are available, photographs
of barnacle larvae. While observing barnacles, please note what other critters are attached or
living among the barnacles.
Barnacles and hydroids (skeletal shrimp were shipped attached to these) become habitat for
numerous species. You should always record what other types of animals are found with
specimens examined. These species are important clues as to the niche occupied by the
animal of interest. We also cannot order many species. Most supply companies will not
collect sea spiders or flatworms for classes. Therefore when we do get lucky to get a
specimen that is not typically available I want the class to examine it, whether we are focusing
on that group in lab or not. If you find specimens that might be of interest to the class, please
share your observations with the instructor and the class. Some of the species you will come
across will look like something out of a fantasy novel. Please again share your observations;
this may be the only time in their lifetime that your classmates and instructor will be able to
observe these specimens.
5. If skeletal shrimp are in ample supply and healthy (not always the case) please record
movies of skeletal shrimp feeding and moving. Please also include some photos of the
shrimp’s habitat. In your journal you will after observing millipedes compare skeletal shrimp
movement to that seen in millipede. Relate differences in locomotion to differences in life
style.
6. Drawing or pics of millipede moving. These are important observations. The millipede
will serve as your model that you use next week for comparative locomotory studies in
crustaceans and insects to the type of locomotion seen probably in the first arthropods
(millipede relatives) that moved on to land. If you are running out of time, these observations
can be done next week, millipedes unlike barnacles and skeletal shrimp, keep well in lab.
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 stereoscope. 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.
1, 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 shrimp cultivated for
food? RECORD YOUR OBSERVATIONS IN YOUR JOURNAL
2. 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 side view), 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 mouthparts move while the shrimp is
feeding?
Gills are located just below the heart.
Make a list of organs you can see in your journal.
3. 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 may not have visible 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
4. Barnacles We have the common 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-arestuck-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.
5. 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 feeding
behavior and if possible their locomotion. 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.
.
c. Make a list of other animals you have found. Include 1-2 photographs of other animals that are
living among the hydroids and the hydroid colony that is home to the skeleton shrimp.
Check with lab instructor about timing. If barnacles are mating or Caprellid shrimp are
plentiful and on healthy hydroid (Cnidarian) colonies, you may want to postpone these
observations until the next lab.
6. You are to observe “model locomotion’’ in an arthropod. The millipede will serve as the model
to which you will compare locomotion in a variety of other arthropods, so you want to make sure that
you can clearly see how the legs or other appendages are used in locomotion. The size of these
large millipedes should enable you to make good observation of how appendages are used.
a. Be sure to note how much of the body moves as a unit when moving forward? When
turning?
b. Transfer your millipede to a sand surface (sand is bumpy and so you may be able to see leg
movement better). What type of tracks would left by the moving millipede? Are they
impressions of appendages on or body segments dragged through the sand? Draw as best
you can by hand (easiest) or use your smart phone to “record” leg movement and tracks.
Draw your impression of the tracks that would be left behind by a millipede.
See example below.
Which of the following tracks would they most resemble?
Millipede track one
Millipede track two
c. Are all appendages moves independently or do a number of legs function as a unit? What
is the effective leg a millipede? Are the legs on alternative sides moved in a tripod motion?
You will be examining arthropod diversity next week.