ZOO 137 - Invertebrate Zoology Phylum Info File -- Cnidaria

Classification You Need To Know

Kingdom Animalia
Subkingdom Metazoa (etymology: ______________________________________________)
Phylum Cnidaria (etymology: ______________________________________________)
This phylum is also referred to by the older name, Coelenterata.
Class Hydrozoa (etymology: _________________________________________)
(examples: ________________________________________________)

Class Scyphozoa (etymology: ________________________________________)
(examples: ________________________________________________)

Class Anthozoa (etymology: _________________________________________)
(examples: ________________________________________________)

Things You Should Do Before Coming to the Lab on Cnidaria

o Memorize the classification given above.
o Study Chapters 6-7 in Animals Without Backbones
o Complete exercises 12-18 in The Zoology Coloring Book (optional but highly recommended)
o Put your dissecting instruments in your backpack; you'll need a scalpel for this lab.

Things You Should Do During the Lab

o Examine the following four prepared slides at your table:

Hydra xs and wm - Two slides of this solitary hydrozoan with no medusa stage; know its life cycle very well. See Figs. 4.4-4.5 in PAZ.

Obelia wm - Two slides, one has a colony of polyps; the other is the medusa stage. Know the life cycle of this animal. See Figs. 4.8-4.11 in PAZ

o Examine the model of Hydra. Here you can easily see that the basic structure of a polyp is essentially a hollow cylinder with an opening (the mouth) at one end (the oral end, as opposed to the opposite, or aboral end). The wall of the cylinder consists of two layers of diverse cells, and the mouth is surrounded by arm-like extensions of the body (the tentacles).

o Examine the model of Metridium, a sea anemone. The polyp body of this animal is also a hollow cylinder, but the body wall is much more complex than that of Hydra mainly as a result of more complex tissues, an invagination called the pharynx (or gullet) and internal partitions called septa. Be sure you can relate the structure of the model to a dissected specimen of Metridium.

o Examine the following demonstration specimens on the front work benches:

-- There will be several types of coral skeletons. Look at them closely. What occupied the very tiny holes?

-- There will be a slide or two showing a strew of Hydra nematocysts, many of which will have their threads extended (discharged).

-- Physalia -- Take a look at the large preserved specimen of this colonial hydrozoan known as the Portuguese-Man 'O War (PAZ 4.12). It is in reality a colony of very highly specialized polyps and medusae. Physalia is a common source of painful stings in warmer marine waters. You will see a short video on this creature in the lecture.

-- The source of Physalia's venom is its nematocysts, that are concentrated by the 100s in the bulbous swellings you can see on its long tentacles. There is a slide showing a xs through one of these bulbs that reveals a whole battery of cnidocytes. What is the relationship between a cnidocyte and a nematocyst?

-- There is a series of slides and specimens showing the life history stages of Aurelia, the moon jellyfish (PAZ 4.13-4.17). Know the life cycle very well -- all the stages, their names and the order they occur in. We will consider it along with that of Obelia in detail during lecture in the larger contexts of alternation of generations, metamorphosis and polymorphism.

-- Note the slide showing a wm of an Aurelia rhopalium. It is a sack-like structure occuring in a notch on the margin of this jellyfish's bell that contains a sensory organ responsible for balance and another sensitive to light.

-- There are several slides of reproductive stages of Hydra. One shows budding, an asexual process. The others show individuals with developed gonads. Note that all these are illustrated in the model.

Things You Should Do After the Lab

o Using all sources available to you, make a list of ten important features, characteristics, etc. of the cnidarians. Don't forget to mention that they're diploblastic metazoans lacking organ systems, the polyp and medusa life history stages, and alternation of generations.

o Be sure to correlate what you've observed in lab with your readings and lecture notes.

o The next lab period will be devoted to a seminar on the hermatypic (reef-building) corals. You may want to re-read pp. 137-147 in Animals Without Backbones. The seminar will last about two hours - remaining lab time can be used to review or complete you study of the lab assignment above . It is a good idea to study the question sheet (see next page) before class so that you'll be prepared to know what to listen for. Material covered in the seminars is tested on the lecture exams, not the lab practicals.