Download Lab 1: Ctenophora, Porifera, Cnidaria

Lab 1 – Ctenophora, Porifera, Cnidaria OEB 51 Lab 1: Ctenophora, Porifera, Cnidaria 03 February 2016 In this course we will be dealing with live animals very often! Take advantage of these opportunities to get to know the organisms, most of which we hardly see in our daily lives. Don’t be afraid to put them under the scope to take a closer look and to manipulate them, but be respectful. Be careful not to get hurt and please take good care of the (precious) equipment of the Lab. Follow the instructions and if you have doubts about how to handle things, don’t hesitate to ask! For today’s lab, consider the following questions: What is the current debate about the first branches to diverge in the Metazoan tree? What types of cell are unique in each of these groups and what do they do? 1 Lab 1 – Ctenophora, Porifera, Cnidaria Ctenophora – OEB 51 Beroe ovate & Mnemiopsis macrydi • Take one ctenophore in a glass dish and bring it to a dissecting scope. Observe its behavior: How do comb jellies propel themselves? What adaptations to pelagic life do they display? • Also observe the structural coloration given by its ctene rows as they beat. Draw the animal in side view and, if possible, in oral or aboral view. Label each diagram with main structures using textbooks. Optional: Dissect a bit of the ctene and mount on a slide. Be careful to observe correct microscope procedure, remembering that NO liquid of ANY kind can be allowed to get on ANY part of the microscope. How long are the cilia? Can you make out individual cilia? • Ctenophores are visually similar to cnidarian medusas, but we know they are actually members of very distinct clades. What are some important characteristics that define each group making one distinctive from the other? 2 Lab 1 – Ctenophora, Porifera, Cnidaria OEB 51 Porifera Hexactinellida – the glass sponges Check out the beautiful dry specimen of Euplectella aspergillum, a deep-­‐sea glass sponge (collected at 2500 m in the Pacific). The sponge has been bleached and the skeleton is extremely fragile. Handle delicately, and always with a barrier between you and the spicules – use gloves. Put it carefully under the stereoscope (dissecting scope). Can you see the hexaxial spicules that give the taxon its name? How do you think the shrimps that you find inside were trapped in the sponge? Demospongiae • Pick a species from the sponge aquarium into a glass dish and observe under the dissecting scope. You may need to cut off a part with a razor blade if the sponge is large. Do a cross section of the body wall using a razor. Make a sketch labeling the main structures of the sponge body and important cell types. Also indicate the direction of the water flow. Does your sponge fit any of the theoretical archetypes (asconoid, syconoid, leuconoid)? If yes, which? Optional: Attempt to identify the sponge using the massive Systema Porifera or the website www.spongeguide.org • Spongilla – a freshwater sponge! Freshwater sponges might be exposed to adverse/variable conditions such as draughts or quick changes in temperature. They have gemmules (highly resistant internal buds) as a means of dormancy. Are there gemmules in this specimen? Make a sketch of its structure based on books or your lecture slides. 3 Lab 1 – Ctenophora, Porifera, Cnidaria OEB 51 Demospongiae (continued) • Spicule preparation Cut a small piece of your living sponge (~2 mm thick) and place it on a small petri dish. Pipette a CHOOSE small drop of bleach on to the sample with a plastic or thin glass pipette. Once the bubbling has ONE stopped, pipette a little seawater on to the bleach/tissue mixture to dilute it, and then take a drop of this sample and prepare a slide. Cover with a cover slip and observe under the compound microscope. How many spicule types do you observe? What types (triaxial, monaxial etc.)? Draw the different spicules. Trade slides with your colleagues to see other kinds of spicules. It is worthwhile to use the Systema Porifera to add to the identification of your sponge – the bulk of species-­‐level taxonomy in sponges is based on spicule morphology. • Disaggregation experiment Sponges are remarkably flexible at the tissue level and, through the action of their amoeboid cells, they can re-­‐aggregate into semi-­‐functional spongelets even after being dissociated into single cells. Cut a small piece (about 2 cm) of Halichondria bowerbanki (Crumb-­‐of-­‐Bread Sponge), Axinella polycapella (Orange Devil’s Finger Sponge), or Lissodendoryx sigmata (Red Rock Sponge), and continuously squish the tissue through cheesecloth into a petri dish with seawater. The seawater should become cloudy with dissociated cells. Once the water settles, pipette an aliquot from the bottom into a petri dish labeled with your name and date. Observe in a dissecting scope and take notes on the size and shape of the disaggregated clusters. Place it on the rocking table and at the end of class examine it again – have they changed observably? Feel free to come back some other day to observe and summarize below. What characteristic of the cells of sponges makes reaggregation possible? Optional variation: mix dissociated cells from two differently colored species into the one petri dish. What do you hypothesize will happen? How do your observations compare with your hypothesis? What do you conclude from these observations? 4 Lab 1 – Ctenophora, Porifera, Cnidaria OEB 51 Cnidaria For each organism, you should ask yourself whether you are looking at a polyp or a medusa, and comment whether the species alternates between the two stages. Characteristic of the phylum, many of these animals sting – so avoid handling them directly and always use gloves. To the adventuresome, it may be a worthwhile experience to feel the mild tingling sting of Cassiopea (the upside-­‐down mangrove jelly) or of one of the anemones yourself – you will also have plenty of opportunity to experience this in Panama! Hydrozoa – Hydra littoralis (freshwater! Use Poland Spring Water) Pipette one or two individuals in a petri dish and observe under the dissecting scope. Then prepare a slide to see in higher magnification under the compound scope. Draw your Hydra indicating the following structures: mouth, tentacles, battery of nematocysts, trunk, epidermis, gastrovascular cavity, basal disc, and gonads and buds (if present). • Feeding behavior Feed your Hydra with a drop of the culture of Daphnia (crustacean – we will learn more about it by the end of the semester). How did the polyp take its prey? Describe your observations. 5 Lab 1 – Ctenophora, Porifera, Cnidaria OEB 51 Cnidaria (continued) The next sections have representatives of all the main subgroups of cnidarians. Choose and closely observe at least one medusa and one polyp among them. Hydrozoa (marine) • Branching hydroids (Pink Hydroid Eudendrium carneum – live) Take a snippet (using scissors) of these plantlike colonial invertebrates and examine closely in a glass dish under a dissecting scope. How many types of zooids do you see? Can you determine their function (reproductive vs. feeding)? Sketch the organisms and label zooids, perisarc, coenosarc and other structures individually (use your lecture slides or Brusca as a guide). You can also snip off a smaller part and make a whole mount to see finer structural details. • Hydromedusa (alive and preserved Gonionemus, Aurelia) These fragile jellyfish are the medusa stage of a colonial hydrozoan. Do your best to produce a labeled illustration, indicating the ring and radial canals of the gastrovascular system, the umbrella, velum, manubrium, gonads, stomach, tentacles and any other structures you observe. 6 Lab 1 – Ctenophora, Porifera, Cnidaria OEB 51 Scyphozoa – the true jellyfish • Cassiopea xamachana – the upside-­‐down mangrove jelly. Isolate an individual in a large glass dish and make labeled sketches (lateral and oral views) of its organization at the gross anatomical level. Pay special attention to its oral arms (extensions of the manubrium) – do you see the secondary mouths? The printed online guide by Richard Fox might be helpful to guide your observations. Cubozoa – the box jellyfish • Preserved cubozoan Draw and label the overall features of this box jellyfish. 7 Lab 1 – Ctenophora, Porifera, Cnidaria OEB 51 Anthozoa – anemones, corals, sea pens, gorgonians • Stony corals (Hexacorallia) Examine the array of calcareous skeletons and choose at least two to draw and label. Were they solitary or colonial? Can you point out individual polyps? • Sea anemones (Hexacorallia) Bring an anemone to a dissecting microscope and illustrate labeling external visible structures. Sketch internal structures based on your textbooks. Anthozoa (Cont.) à à 8 Lab 1 – Ctenophora, Porifera, Cnidaria OEB 51 Anthozoa (continued) • Sea pansy (Octocorallia) – Renilla mulleri This species is adapted to life on soft benthic substrata. Draw and label indicating the feature that allows it to anchor into soft sediment. Look at higher magnification to observe and draw a polyp. How many tentacles does it have? • Sea pens and gorgonians (Octocorallia) Use a razor to snap off a branch of one of these colorful colonial animals and observe them closely in a glass dish. How would you describe the mechanical properties of the colony – is it easy to cut? Have you ever seen the polyps of these soft corals? In a small petri dish, relax the polyps in MgCl2 to induce them to come out of their skeleton. How many tentacles do they have? Make a sketch and label the main structures. 9 Lab 1 – Ctenophora, Porifera, Cnidaria OEB 51 • Nematocysts Dissect off a tentacle of any of the cnidarians and make a wet mount on a slide (you can also use your Hydra slide). Observe them on the compound microscope and look for nematocysts, discharged and undischarged. You may need to take the excess water off to slightly squash the tentacle. Draw the nematocysts at high magnification (400X) and label according to the textbooks. 10