Arthropod survey.
Part one.
Aquatic crustaceans
Please examine tagmata and locomotion in three different crustaceans. 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.
All containers should be rinsed with spring water before organisms are placed in
them.
Daphnia
Everyone should look at locomotion in Daphnia, the common water flea. These are
highly transparent organisms and you can easily a. compare their anatomy
to that of the Caprellid shrimp of last week. Are any females carrying
eggs? Daphnia when crowded becomes pink to red as it develops
hemoglobin. Can you think of any reasons for this? Is there any evidence
that our cultures have individuals that have developed haemoglobin?
Also make sure you can describe in some detail how Daphnia uses its
appendages to move. Compare the way Daphnia moves to that of the
Caprellid shrimp or glass shrimp. Obtain a movie of Daphnia movement.
A reference diagram for Daphnia
Examine the isopods and one of the other aquatic crustaceans available.
Freshwater amphipods.
a. Obtain a photograph and b. label regions, head, thorax and abdomen and c.
describe how appendages are used in locomotion.
Freshwater isopod. a. Obtain a photograph and b. label regions and c. describe
how appendages are used in locomotion. d. You will compare these fresh
water isopods 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.
Freshwater 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.
a. 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. b. Describe how these animals locomote.
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.
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.
Ostracods
We do not have ostracods today, but a diagram of these animals is included because
you may also see a number of marine ostracods on your specimens in the future.
An ostracod is a segmented crustacean with head, thorax and abdomen. The
head has very hairy legs and usually at least one eye. The rest of the body is
very short and ends in a multi-pronged tail (furca). The whole body is enclosed in
the carapace, which hinges on the back and is held shut by strong muscles.
Sometimes the antennae can be extruded through a notch at the front. Most
ostracods are very small, fewer more than 4 mm long but some deep-water
pelagic species grow to 30 mm.
Sexy shrimp
Before you begin to work with terrestrial forms, check on the sexy shrimp, Thor
amboinensis, in the aquarium. These animals sways their abdomens back and
forth in a style determined sexy, hence their name. Many functions have been
postulated for the swaying, among them territorial defense, mating, etc. You
may have used them as a model for locomotion last week. Do you notice any
groupings? Are the animals more active in groups?
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Terrestrial arthropods
Pillbugs
Examine the pill bugs or land isopods available. There are about three 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?
Millipedes
Obtain a millipede. Make sure you record whether you are working with Sigmoria
aberrans (black with yellow or pink on edges) or Narceus americana (longer
than Sigmoria and uniform in coloration).
Count the number of legs found per segment.
Observe and record if you can locomotion in the millipede. How much of
the body moves as a unit when moving forward? When turning?
Transfer your millipede to a wet but firm sand surface or special paper
(inked or sonagraph(. What type of tracks are left by the moving
millipede? Are they impressions of appendages on or body segments
dragged through the sand?
d. Which of the following tracks do they most resemble?
Millipede track one
Millipede track two
Draw as best you can in Photoshop or use your smart phone to “record”
the tracks left behind.
Photoshop instructions: You can simply ask for a new file, specifying one about
6 by 6 inches. Then use a small sized paintbrush in any color you wish to draw
your tracks.
See example below.
Groups choosing different species should compare their results. You should also try to
see if the sowbugs will be willing to walk for you and compare their tracks to that
of the millipedes.
INSECTS
Insects are the most successful land group.
Bessbugs or ladybugs
Compare the tagmatization found in one of the cultures of insects to that of
the shrimp you photographed last week.
Observe "walking" in an insect. Which legs move together? Compare its
movements to that of the pill bug and millipede. You may be able to make
it walk across the sand surface so you can compare the tracks made by it
and the millipede.
Bessbugs
These harmless beetles live in and under moist, rotting wood. Bessbugs are paternal
and adults will chew up wood and feed it to the young larvae. A common species
is Odontotaenius disjunctus but our supplier does not identify their cultures.
Adults stridulate by rubbing abdomen against the wings. Larvae stridulate with
reduced third pair of legs–these scratch against other legs.”
Ladybugs.
Roaches
Not quite insects!!
Springtails or Colembola.
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.
Everyone should examine the springtails because they are so common and one of the
most numerous arthropods found in any sample containing moss. Observe springtail
movement. How do they use their legs as opposed to the furcula? Try to obtain a
photograph, but do not open the petri dishes. These guys are great escape artists.
You will not have to label the photograph, but it will serve to document your efforts.
Generally the slide of the pseudo scorpion is our only representative of the group
Arachnida.