1
Arthropod diversity.
Objectives:
Redo observations on barnacles.
New activities.
1. Observe living crustaceans and examine how they use their various appendages and antennae in different ways. Pages 1-6.
2. Begin to appreciate Hexapod diversity. Pages 6-10.
3. Examine slides of arachnids. Pages 10-11.
4. Examine living representatives of smaller clades. Pages 11-13.
1. Aquatic crustaceans
Crustaceans are noted for using their many appendages in various way.
Please examine tagmata and locomotion in two different aquatic crustaceans. You may be asked to further examine internal morphology or compare the locomotion of a particular species to a terrestrial form.
You should obtain a picture of each and be able to describe the types, number of appendages and how they and other structures are used in locomotion in each species. Are they using the whole appendages as the “effective” leg or just part of it to move? Your pictures should label antennae and “legs”. Your descriptions should include any tagmata you can see.
We have a new order of skeletal shrimp. You may want to use them as one of your species. All containers should be rinsed with spring water before organisms are placed in them. Most of the crustaceans you will need to view are freshwater. The skeletal shrimp are the exception; they are marine.
a. Daphnia
These are highly transparent organisms and you can easily view their anatomy. Are any females carrying eggs? Daphnia when crowded becomes pink to red as individuals develop hemoglobin. Can you think of any reasons for this? Is there any evidence that our cultures have individuals that have developed hemoglobin? Locate the heart and gills and compare their location to the location of the same organs in the shrimp you worked with last week. Obtain a few photographs of Daphnia to document your observations.
Obtain a movie of Daphnia movement . Your journal should also contain a paragraph on how Daphnia uses its appendages to move. Compare the way Daphnia moves to that the glass shrimp you worked with last week in your journal. You may use the movie from your first lab if you feel it is good enough.
A reference diagram for Daphnia
b. Freshwater isopod. Obtain a photograph, label regions, and describe how appendages are used in locomotion. If you choose these species, you should also compare how these fresh water isopods locomote to the terrestrial isopods or pill bugs. As in most crustaceans, the isopod body is divided into three distinct regions: head (= cephalon), thorax (=pereon), and abdomen (= pleon). Please use the more general terms, head, thorax and abdomen for labels on your photograph.
Pillbugs
Examine the pill bugs or land isopods available. There are several species of varying size and color that are living happily together in an aquarium. All are US natives.
Compare its morphology to the fresh water amphipod or isopod that you observed.
Compare how it uses its legs to walk with how the fresh water amphipod used its limbs to swim?
c. Freshwater amphipods.
Obtain a photograph and label regions, head, thorax and abdomen. Describe how appendages are used in locomotion.
Pillbug comparisons
Examine the pill bugs or land isopods available. There are several species of varying size and color that are living happily together in an aquarium. All are US natives.
Compare its morphology to the fresh water amphipod or isopod that you observed.
Compare how it uses its legs to walk with how the fresh water amphipod used its limbs to swim?
d. Freshwater or saltwater Copepod. Cope is greek meaning an “oar” or “paddle;” pod is Greek for “foot.” This should serve as a hint for how these individuals move. You will probably find copepods on most of the marine specimens you will view in the future and so you need to be able to recognize these small animals.
Obtain a good image of a copepod for your journal. You may have to place a copepod on a slide under the light microscope to obtain a good image. Describe how these animals locomote. Can you see egg sac on any of the specimens?
We do have marine copepods, which are bigger than freshwater forms, that you can examine. However, do not mix salt water with fresh. Rinse your dishes with several washes of spring water after viewing marine copepods. Marine specimens can tolerate some fluctuations in salinity. Your freshwater specimens however cannot be put in salt water
e. Freshwater crayfish. We keep a Procambarus sp. first found in Germany. It is an unusual species in that males are lacking. This variety is know for being parthenogenetic. Meiosis is suppressed in females, who essentially clone themselves whenever they produce eggs.
Unfortunately, none of our females are carrying eggs. However, if you wish to use one of these for examining locomotion in fresh-water crustacean, feel free to do so. Take good notes, as you will not be able to film these species. Those of you with smart phones may want to click a few shots and email the pictures to yourself for your journal. In your journal, compare their structure and locomotion to the freshwater shrimp you viewed last week.
f. Caprellids. These are truly spectacular creatures to watch feed and move. Please obtain a film of their feeding behavior and if possible their locomotion. You should also be able to obtain photographs of overall structure to label. Label antennae and peropods at least in photographs.
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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.
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2. Hexapoda
a. Springtails or Collembola compared to termites.
Although considered hexapods (having six legs), springtails are not considered true insects. It is because their mouthparts are not free as in most insects. Go ahead and examine the head on high power and compare the head of a springtail to that of a termite or true insect of about the same size.
Obtain a photograph of the springtail and termite. Label antennae, head and abdomen in both species. Describe which body structure contains the legs. The springtails are in petri dishes and so will not “jump” or use their furcula. To see this structure, please view one of the slides we have available of Collembola.
The name Collembola, derived from the Greek "coll" meaning glue and "embol" meaning a wedge, refers to a peg-shaped structure, the collophore, on the underside of the first abdominal segment. The collophore was once thought to function as an adhesive organ, now is thought to play a role in osmoregulation. These were once considered insects, now placed in a separate group under the Hexapoda, a group that also contains the insects. They are also known as springtails because of their forked jumping organ (the furcula) found on the fourth abdominal segment.
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Termites are true insects. They are social and many species have castes, or individuals that differ in morphology and their role in termite society. You should have some workers and perhaps a soldier (larger, larger head and jaws) in your petri dish. Do note the exposed mouthparts. Take a photograph of your termite and label as many body parts as you can. I could not find a labeled diagram of a termite for you, so the grasshopper diagram will have to suffice for common structures found in most insects..
b. Choose one of the following species to examine. Compare locomotion and tagmatization in one of these species to that of the termite.
Darkling Beetles.. Please compare adults to larvae if they are available. Newly hatched larvae are almost microscopic and may molt 50 times or more before reaching pupation size.
Domino roaches
Adults are beetle mimics, possibly of Anthia sp. tiger beetles. Nymphs tend to be more roach like and to burrow during the day, These roaches feed primarily on dried leaves, but love small bits of protein-based pet foods and fruit.
Desert beetles.
Flightless beetles often seen trudging across trails and over sandy terrain. If bothered, the beetle does a headstand, signaling that it's ready to squirt a noxious substance onto an assailant. The spray is foul to the nose, and isn't dangerous to people.
Activity c. Parasitic insects:
If time permits, look at the slides of lice. My daughter came home with these a few times from school. Lice are insects but modified structurally for their ectoparasitic lifestyle. There are three species that infect humans, identified by structure and habitat, hair, body or pubic area. You will be asked to compare the structure of one of these species to those of the eyebrow mite. Make sure in your journal you note the species that you examined.
3. Arachnids : Please examine a slide of a pseudoscorpion and hair follicle mite.
a. Pseudo scorpions. Compare the tagmata of Pseudo scorpions to that found in insects and crustaceans. Verify your examination by obtaining a labeled photograph for your journal. Pseudo scorpions are predators feeding on ants, mites and small flies among other small arthropods. Many species spin silk from a gland in their jaws to make cocoons for mating, etc. They do have venom glands located within their palps.
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b. Note the adaptations for a parasitic life cycle on mites found on humans primarily in the hair follicles of eyelashes and eyebrows. Two species have been identified and we have slides of Demodex folliculorum. The adult mites are only about .4 millimetres long with an very elongated body. The mites can leave the follicles and walk around on the skin at night. Almost all adults over the age of 17 carry them. It is only in rare cases that the mites result in any skin eruptions.
The species that infects dogs however can result in serious disease (mange).
Obtain a photograph and compare the overall structure of the mite to that of the pseudoscorpion or to that of a typical spider diagrammed below. .
4. Examination of smaller clades.
a. Limulus: Count the number of legs and see if you can identify the gnathobase or grinding organ. Food often encased in a hard shell or exoskeleton is guided by the chiliarium through the legs and to the gnathobase. After being ground here, the chelicerae are used to place it in the mouth.
Can you locate the book gills, which serve as respiratory organs?
b, Sea spiders, if available: Describe the overall anatomy of the spider. Estimate the length of the body to that of the long legs. Note that the "body" is not that much thicker than the legs, although terming the central cylinder a body is somewhat misleading as part of the GI tract + extend into the legs.
Dorsal surface showing proboscis, eyes and chelifores (appendages used
to tear bits of food).
Ventral surface showing oviger (used by males to carry eggs) and gonopores or opening to reproductive organs.
Describe locomotion in these animals. Obtain a photograph if possible showing the oviger.