Additional specimens for lab:
We must be opportunistic about examining specimens during their reproductive
season, even if it does not coincide with our schedule. Often a week or two can
make a big difference in observing active organisms or colonies versus inactive
organisms or colonies. A cyst or egg left by a specimen is not as exciting as the
active adult. So this lab brings with specimens ordered the following organisms.
5. WE HAVE SEA SPIDERS!!!!!
A small species has hitch a ride on the cnidarian colony on which skeleton
shrimp were shipped.
There are four specimens in a small dish labeled sea spiders. I am asking the
instructor to set these up and have everyone as they prepare their second plate
for sponge re-association observe these animals. I want to add that a professor
who studies sea snakes and so diving a lot never saw these until last year in this
class. Take this opportunity to view these species. It may be the only time in
your life you view a specimen. We apparently even have a male carrying eggs.
Each pair that examines this should take one shot or make a short film for the
class. I will make the picks available for your journals. You are to describe the
animals and how they move in your journals.
IF YOU FIND MORE WHILE EXAMINING THE HYDROID COLONY, PLEASE
ADD THEM TO OUR DISH OF SPIDERS. WE’LL TRY TO KEEP THEM FOR
AS LONG AS POSSIBLE.
6. The hydroid colony that came in with the shrimp is shedding medusae.
WOW!
You should obtain a sample of the colony. a. Attempt to film feeding. If you
are lucky, you will have a stolon that contains not only feeding polyps, but
also medusae that develop on the side of a feeding stationary polyp.
When you return your specimen, look at the bottom of the dish; it may also
contain shed medusae. Medusas that pulse are ready to be put in a kreisel
tank to start the next stage of the life cycle.
A diagram of the life cycle of Obelia, a common hydrozoan.
We have obtained a colony of Pennaria. Below is a diagram for P. tiarella,
showing an active but not reproducing colony, but with an insert showing
medusae developing on the side of the feeding polyp. b. Compare your
photograph of the colony to the diagram. Label a medusa and a feeding
polyp.
In Pennaria sp. medusa buds develop along sides of feeding hydranths. Be
careful, use gloves, Pennaria medusae as all medusae and polyps sting (even
the Hydra you observed in high-school), although these are so small I don’t
expect even if they contact skin, you will feel anything. Generally colonies are
male or female, although the medusae of both sexes look alike.
c. Describe colony structure in your notebook. How much stolon (brown
base) is found between feeding polyps? Where are the feeding polyps found?
Are budding medusae found on all polyps? Take lots of pictures. If the colonies
we get in next week are not reproducing you will use these pictures as an
example of a reproducing colony.
d. Take a picture of medusae that has been released at the highest power
of the stereoscope. Next week you will compare these medusae to those
belonging to another subclade of Cnidaria.
7. Bryozoans
We have obtained several species of bryozoans, including two that form open
branching colonies. The branches connecting individuals are also called stolons
but the individual feeding units are known as zooids. Although superficially they
look like hydrozoans, they are not at all closely related. Bryozoans feed by using
a lophophore. Bryozoans use the lophophore to filter feed while hydrozoans use
their tentacles to sting and capture prey. Compare their size to that of a
predatory hydroid. These are complex creatures with organ systems reduced
because of that size, but they as you will see later have coeloms and well
developed muscles, so definitely triploblastic as opposed to the larger but more
simple basically bilayer hydrozoans. Again structure for later but film what you
can of movement of the lophophore as well as what in happening muscle wise in
that transparent body. It will become evident that muscle are controlling that
lophophore.
a. Take movies and picture of feeding zooids. We may not get active colonies
later in the year and any films you take today may have to suffice. Again just
take good videos of these specimens feeding (essentially moving their
lophophore in and out and stash them in a safe place for when we will get to
study these interesting
creatures.
b. We also have bryozoans with avicularia. Bryozoans show polymorphism with
some individuals depending on the species not developing into lophophore
feeders but zooids that will defend the colony. In most colonies they can be
found where eggs are normally housed, below the feeders near where branches
begin. This is the first time in 5 years we have had a species that has avicularia.
Everyone show watch these in action. The specimens with these parrot beak
like zooids should be set up as a class demo with every pair at least
attempting a photo at high power. Those with time should try a short video
on their defensive behavior.
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Finally we have all shorts of non-branching encrusting bryozoans. These have
mineralized exoskeletons and look like very small corals. A close inspection will
show the orifice through which the lophophore protrudes. Just examine these,
they tend to be more sensitive to light and almost never show their lophophores
even if they are active colonies.
I want you to start recognizing these as Bryozoan and be able to
distinguish them from tunicates which are also filter feeders. In these,
water is brought in one siphon and expelled in another. Particles to be kept are
trapped by an internal basket.
Colonies of small tunicates appear gelatinous, they may be very colorful,
incorporating into their bodies minerals that color them gold, orange or bright
blue.
8. Tunicates: Right now just examine the various tunicates. If you have
time, you can take one of the larger transparent specimens, put some
phytoplankton near a siphon and watch it draw water in. The whole body of the
tunicate contracts to bring water in and out. They are some of the invertebrates
most closely related to us. Again , I think we can probably get some more later in
the term, but do what you can with some of these active specimens if time
permits.
Yes, this lab finally ends; this delivery was almost too much of a good thing!