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!