Lab 11 – Lophophorata Bryozoans live as colonies, a collection of attached individuals termed zooids
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| Lab 11 – Lophophorata
Bryozoans live as colonies, a collection of attached individuals termed zooids, formed by asexual budding from one metamorphosed larva. Zooids secrete an exoskeleton that gives the colony its hard texture. The living tissue of the zooid is the polypide, including the internal organs and the feeding structure, the lophophore. A zooid extends this retractable circle of ciliated tentacles by pressurizing the coelom to push fluid into the tentacles, thus inflating them. STATION 1 – branching bryozoans Bugula neritina or B. californica Examine by eye, under the dissecting scope, and then compound scope; at each level of magnification, draw the colony structure you observe. How do these colonies compare with encrusting species? How could you distinguish this animal from a hydroid colony? Look for round gonozooids, and avicularia, clawlike zooids that snap or flick; what purpose do you hypothesize such structures might serve? Think about how sponges use chemistry to survive as sessile invertebrates, and hypothesize similar functions avicularia may serve for bryozoans. Speaking of chemical defense, Bugula harbors a unique bacterial symbiont which it passes on to its large, slow-swimming larvae; the symbiont produces bryostatins, defensive compounds that are toxic at high levels and are under study as potential anti-cancer drugs. STATION 2 – the bryozoan Membranipora membranipora Membranipora commonly fouls the surfaces of algae. Each round, white colony consists of many tiny, interconnected zooids. Under the stereoscope, observe how the zooids extend their lophophores and feed. Use the handouts to identify features of the colony. Observe tiny particles whirling around the lophophore to detect the direction of water movement through the tentacles. Examine live colonies, looking for the operculum or defensive spines. Colonies sense chemicals leaking from their predator, the nudibranch Corambe pacifica, and grow spines from each corner of the zooid to protect themselves from being chomped. Do you see any spines, or empty zooids that may have been eaten? You may find the highly cryptic Corambe living on Membranipora, perfectly disguised as part of the colony on which it feeds. How do you think tiny, slow, highly specialized predators find their specific prey? STATION 3 – encrusting bryozoan Some bryozoans are encrusting, forming flat sheets on hard substrates like mussel shells. Choose one of these colonies and compare the colony structure, and the appearance of the lophophores, to the other stations. Note features like the operculum (draw a close-up view if possible), any spines, or large reproductive gonozooids if present. STATION 4 – Phidolopora pacifica This bryozoan forms upright colonies with a complex 3-D architecture. To me they resemble piles of orange cornflakes glued together; the clumps can be very large, and are one of the most striking things to see when scuba diving locally. Do the lophophores extend from all surfaces of the colony, or is there a pattern to how they are arranged within the 3D matrix of zooids? STATION 5 – the foliose Filicrisia This bryozoan grows as a branching colony of tightly packed zooids. Do you see an operculum or spines present? Note the large, round ovicells (or gonozooids), the reproductive zooids in the colony; how do they compare to the feeding zooids? Compare the overall colony shape and structure to that of Bugula and Phidolopora. STATION 6 – the entoproct Barentsia benedeni Entoprocts have been lumped with, and then split from, bryozoans in many cycles by systematists who could not reconcile their adult similarities with their embryonic differences. Molecular analyses support a close relationship of these groups. The stalk may be jointed in B. benedeni, allowing the animal to bend and flex. In other species there are no joints, so if you can’t find any this may be a different species of Barentsia. Observe the movement of individual stalks. Each individual has a calyx, a ring from which the feeding tentacles extend. Try to observe the water flow through the tentacles of Barentsia using a tiny amount of red dye, or naturally occurring particles. Compare this to water flow around a bryozoan lophophore -- can you observe the fundamental differences in how water moves through these different kinds of tentacle-rings? Through their clear bodies, you can see the whole digestive system from mouth to stomach (containing whirling food particles) to anus; both openings are inside the ring of tentacles, unlike bryozoans. Observe their flinching feeding behavior, and compare this to how lophophores function. STATION 7 – the phoronid Phoronis australis These are the preserved bodies of Phoronis australis, which I collected in Australia in a bay infested with great white sharks (no lie; I risk my life for this class..) This species has a peculiar habitat: they attach to the tubes made by cerianthid sea anemones, so that you see dozens of black lophophores sticking out of the mud all around each anemone. Observe the lophophore, and compare it to those of the bryozoans you saw. Can you see the 3-part arrangement of body regions? Can you locate the mouth and anus? What features, if any, would let you tell this was NOT an annelid worm? Note also that preserved with this adult were clumps of actinotroch larvae being brooded in the mouth, which may fall out into the dish as white clumps; examine some under the compound microscope. This larval form is unique to phoronids; what does it look like to you? STATION 8 – Articulate Brachiopods Following the handout, draw the visible features of both classes of brachiopods. How does the articulate brachiopod shell compare to the shell of a clam or mussel -- what are the similarities and differences? What do you think the word “articulate” means in the name of this group (hint: what does articulation mean, in the sense of transferring course credit between institutions?) STATION 9 –Inarticulate Brachiopods Follow the handout to describe the external anatomy of an inarticulate brachiopod. How does it compare to the articulate brachiopod, and to a bivalve mollusc? |