|Lab 4 – Cnidaria, Classes Scyphozoa and Hydrozoa
Station 1 – Class Scyphozoa: Medusa stage of the jelly Phacellophora.
These are medusae of the genus Phacellophora. The 4 gastric pouches of the GVC which are clearly visible as pink regions (the color is from their lab diet of brine shrimp.) Unlike most jellies, Phacellophora does not feed by capturing large prey; it feeds by catching small particles or tiny animals from the water. Pipette a small amount of live brine shrimp into the tank near a jelly, and observe its feeding methods. CAUTION: do not touch the jelly if you are allergic to bees, as there is a chance you might be allergic to its sting. ALSO: do NOT get air bubbles under the bell of the jellyfish or it will die.
Adult medusae are gonochoristic, and the gonads are visible on these specimens adjacent to the gastric pouches. If there is a specimen laid out under the dissecting scope, draw it and label the main features (pp. 46-48 of the handout). Look particularly for the following:
Oral arms Mouth
Gonads Gastric pouches
Ring canal Perradial canal
Subgenital pit opening
Station 2 – Polypoid stage of Phacellophora
Phacellophora starts life as one of these polyps (scyphistomae). Observe one under the microscope and draw it. Look for 4 pits extending downwards from the oral surface. Look for a strobilating polyp and draw what you see.
Station 3 – Ephyra stage of Phacellophora
These beakers contain the ephyrae, or juvenile medusae, of Phacellophora. Examine one ephyra under the dissecting scope. What features can you see (pp. 46-49)? Pipette a small amount of live brine shrimp into a dish with your ephyra to observe its feeding. Are the gastric pouches of the GVC visible? (pink regions; the color is from their lab diet of brine shrimp.) Look for the rhopalium, a specialized sense organ at the end of each arm (see p. 49).
Station 4 – Class Hydrozoa: the colonial hydrozoan Hydractinia
This little colony of polyps belongs to Class Hydrozoa. How does it compare to the other hydroids you will see in Station 5? There may be evidence of polymorphism in this colony, meaning that some polyps will have distinct morphologies. Look for longer, heavily armed dactylozooids involved in defense; feeding gastrozooids; and/or gonozooids with reproductive structures. How do the individuals in a colony survive if only a few are successful at catching food?
Station 5 – Class Hydrozoa: live hydroid polyp morphology (CHOOSE 3)
Most members of the Class Hydrozoa have dimorphic life cycles consisting of polyps and medusae. Benthic polyps grow asexually, and give rise to pelagic (free-swimming) medusae that have sex. Hydroids are common fouling organisms in marine environments, meaning they grow on any exposed surfaces, including other animals. There are several kinds of unknown hydroids growing on various substrates – pieces of dead algae, rocks, wood. Hydroids are members of fouling communities, the term for an assemblage of organisms that colonizes any submerged hard surface in the ocean.
CHOOSE THREE different kinds, and follow the directions below for each one.
For each species: remove one hydrocaulus (like a stem) and observe it in a small dish of water—are the polyps alive, and extended? Is this a thecate or an athecate hydroid – is there a clear covering over the polyp, or just the hydrocaulus? Do you see any reproductive polyps or structures?
Draw the structure of a colony, and one polyp up close; refer to pages 28 + 32 and look for:
Hydranth Hydrotheca Perisarc
Mouth Hydrorhiza Gonozooid
Try to identify each species, using the blue book or web resources; might not be possible to identify even to the genus level, but try your best.