body plans - lophotrochozoa PDF

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body plans
lophotrochozoa...

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Week 3. The Lophotrochozoa Aims of this session: ● ● ● ●

To look at the group lophotrochozoa and understand why they are grouped together. To consider body plans – symmetry and body cavities (acoelomate and eucoelomate), segmented vs non-segmented. To be aware of the immense diversity of annelid, platyhelminth and mollusc forms. To learn some more taxonomy and revisit the tree of life.

Don’t panic if you cannot finish this. It is formative which means it is to guide you in your reading. You can get many of the answers in a text book or by visiting the museum. What does the name lophotrochozoa mean? What animal phyla are in this clade? Only three phyla will be covered in the practical in any detail because they are members of the Big Nine: ● ● ●

Phylum Annelida Phylum Mollusca Phylum Platyhelminthes

There will be some examples of other phyla for you to see: ● ● ●

Phylum Nemertea Phylum Acanthocephala Phylum Brachiopoda

GO round the stations (not necessarily in the order given, choose somewhere with space) and try to answer questions and undertake tasks. Note the time you are allocated for this. Station 1 Phylum Platyhelminthes – G6 and Case 2. 20 – 25 min

The Phylum Platyhelminthes are flatworms, found in marine, freshwater and terrestrial habitats. They have three tissue layers. Classes Cestoda, Turbellaria, Trematoda . The station includes microscopes with some glass slides with platyhelminths from three different classes. Look also at case 2 in the Cole museum. ● ● ● ●

Look at these. MAKE SURE YOU CONTACT A DEMONSTRATOR BEFORE USING A MICROSCOPE if you are not sure how to use one. What body plan do platyhelminths have? Look at your class notes. Look at Fasciola and draw it. Note the lack of a coelom. Can you see the sucker? Why does it have this? parasitic Take a look at the tapeworm. Some don’t have guts. Why do you think this is? Where does it live? They live inside guts of vertebrates. They are very think and absorb nutrients directly.

When you get home, look up the tapeworm life cycle. Examine the live planarian in some distilled water in a petri dish under a low-power dissecting microscope. This is in the Class Turbellaria and it lives in fresh water. Unlike many tapeworms it is not parasitic and has a pharynx that can be protruded from the mouth. It is carnivorous, eating other invertebrates. Watch the way it moves and describe it. Look up movement in planaria when you get home. Can you identify the head end and the light sensitive spots? Add a little food to the dish and observe. How does it feed? With a pharynx

Station 2. Phylum Annelida – G6 and Case 2 20 min

Annelids are segmented worms divided into two main groups: Errantia and Sedentaria. What do these names refer to? What type of body plan do they have (symmetry, body cavity)? ●

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The station includes microscopes with some glass slides with Class Errantia annelid cross sections. Look at these. MAKE SURE YOU CONTACT A DEMONSTRATOR BEFORE USING A MICROSCOPE if you are not sure how to use one. Note that the intestine is separated by the coelom from the body wall. Worms from the Class Sedentaria (Polychaetes) live in the sea. Many are carnivorous with jaws. They are characterised by parapodia used for locomotion and gas exchange. Make sure that you look at these on the specimens in front of you and draw one if you have the time. These worms are highly derived and look like aliens. They are traditionally called polychaetes but recent molecular work has put them outside both the Sedentaria and Errantia groups in the group Chaetopteridae. This worm is called Sipuncula or peanut worm. It was thought to be in its own phylum, but molecular work has shown that it is a derived annelid. Note the segmentation.

Station 3. Phylum Annelida – G6 and case 2 15-20 min

This station has specimens of live earthworms which are in the Class Errantia. Look at your worm. What is the saddle called and what is its function? ● ● ● ●

You will find sheets of glass and paper. Put a worm on the surface of the paper and watch it move. Put your ear to the paper. What do you hear? What is making this sound? Scraping. It shows that they have hairs. Now put the worm on a piece of glass. Is it moving? If not, why not? If the glass is clean it shouldn’t be able to move. Put the worm back on paper and watch it move. Which parts are moving? Make notes. When you go home, look up worm locomotion and hydrostatic skeletons.

Station 4 – Phylum Mollusca and Phylum Brachiopoda G6 and Cases 2, 6 and 7. 15-20 min

Mollusca is the second largest animal phylum after Arthropoda All molluscs have a ventral muscular foot and a mantle. The mantel is a dorsal tissue layer that deposits the shell. Class Bivalvia and Phylum Brachiopoda Bivalves have two shells hinged together at the dorsal apex. Bivalves do not have radulas. Have a look at the bivalve shells provided. The apex of each valve has a hump called an umbo. From the umbo to the edge, you may see growth lines which indicate the age of your shell. How old do you think it is? Look inside and observe the scars where the muscle attached. Draw this and label. Look at the specimen in the glass jar. This is called lingula. It is in the same phylum as the fossil specimens provided. How are they similar and how are they dissimilar? Describe. If you hold a brachiopod in your hand so that you are only looking at one valve of the shell, and then you flip it over to look at the other valve of the shell, you'll notice they aren't the same. Do the same thing with a bivalve, and you'll notice they are. If you were to look at the two valves of a bivalve shell you would see that they are, in fact, mirror images of each other (with a few exceptions, most notably the oysters). This means that the plane of symmetry in a bivalve runs right along the hinge line. For brachiopods, it's the opposite. The plane of symmetry in brachiopods runs perpendicular to the hinge line; if you cut a brachiopod in half perpendicular to the hinge line, you would see that both halves are mirror images of each other

Station 5 and Case 6. 20 min

Class Gastropoda and Polyplacophora What do the names mean? ●

Many gastropods have coiled shells and some have an operculum which is effectively a gate. Have a look at the examples of empty shells provided. These include limpets that have no coiling. Look at the Helix shells (terrestrial) and compare to the marine shells. What is the difference?

Terrestrial shells look more fragile ●

Under the microscope you will see a Crepidula veliger. MAKE SURE YOU CONTACT A DEMONSTRATOR BEFORE USING A MICROSCOPE if you are not sure how to use one. Crepidula are the slipper limpets that have invade the UK coast. What is a veliger and where does it fit in the mollusc life cycle?

It’s a planktonic larva between the egg or trochophore and adult.

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Many snails have what is called torsion. Look at the preserved snail outside of its shell. The body is twisted. Look up torsion. What is the function?

During torsion visceral and pallial organs change their position by twisting through 180°. Posterior mantle cavity is brought to the front position. Gills and kidney move from left to right side and in front which helps in breathing. In nervous system the two pleurovisceral connectives cross themselves into a figure of 8, one passing above the intestine and the other below it. Alimentary canal twists in the visceral mass and opens by anus on the side of the head on the anterior side. As gastropod shell has only one opening, it has to serve as entrance as well as exit for all visceral organs. Both mouth and anus must open on the anterior side. Mantle cavity also must open on the anterior side for easy respiration. Respiratory current opposes locomotion after torsion which increases availability of water inside the branchial chamber. Visceral mass has to undergo rearrangement so that openings of kidneys, gonads and anus should migrate to the front side which is the only opening of the shell ●

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Snails have slime glands at the front of their foot to secrete mucus. Put a live land snail on a piece of glass and watch it move. How does it use its foot and the slime? Feed it a bit of lettuce and see if you can observe the radula by looking underneath the glass. Examine the external anatomy of the chiton. DON’T TIP THE CONTAINER. Note the 8 overlapping shell plates and a leathery girdle to protect the dorsal surface. Chitons also have a large broad food. Not all gastropods have shells. Slugs and nudibranchs (sea slugs) don’t all have shells. Here is a model nudibranch. Please don’t touch it since it is fragile. If you go into the museum you can see a large sea hare nudibranch in case 6.

When you go home, look up sea slugs on the internet and see how beautiful they are! I named my cat Doris after one found in the UK. Can you guess which one? Station 6. G6 and case 7 15 min Class Cephalopoda What does Cephalopod mean? Go and read the information in case 7. These are highly derived molluscs. What does that mean? That they have evolved away from the normal form of the phylum.

Have a look at the specimens on display in both G6 and case 7 which include a squid, octopus, nautilus shell and cuttlefish bone. The extinct ammonites are related to which of these? Look at either the squid or the octopus. Note the tentacles with suction discs. Cephalopods have a radula but the function is to move the prey to the beak. In many species the mantle has been modified into a contractible muscular sac for propulsion. The foot has evolved into the arms and tentacles. When you go home, look up the difference between arms and tentacles to make sure you don’t irritate a cephalopod biologist.

Tentacles are long, flexible organs found on

invertebrate animals. They are important for feeding, sensing and grasping. Tentacles are longer than arms, are retractable and have a flattened tip that

is covered in suckers. Arms are similar to tentacles, but still distinctly different. Arms are covered with suckers that help with grasping food items. In addition, these arms are useful to attach to surfaces while resting. The names may seem interchangeable, but when it comes to cephalopods, there’s a difference between arms and tentacles. An easy way to spot the difference is that arms have suckers along their entire length, while tentacles only have suckers at the tip.

Station 7. Mystery specimens. This is for interest only.

Try and identify these as much as you can, from phylum down to class. ● ● ● ● ●

Look at this marine animal down a low-powered microscope without removing it from its tube. MAKE SURE YOU CONTACT A DEMONSTRATOR BEFORE USING A MICROSCOPE if you are not sure how to use one. This is the remains of an animal found on the sea shore in the Mediterranean. Look at the animal in this tube down a low-powered microscope. These animals live on seaweed. These are marine animals found around the coast of Britain. Look at the two photographs. Try and identify.

Ask a demonstrator to give you the answers once you have had a guess. Were you right? Are you surprised?

Station 8. Cole Museum case number 2. Homework.

Phylum Nemertea, Acanthocephala and Brachiopoda – questions to consider. You can do this outside of class by reference to the lecture and books. ● ● ● ● ● ● ● ●

What features puts Annelids in the same group as Molluscs? Trochophore larva How would you identify a specimen as a Brachiopod rather than a bivalve? symmetry What does the name Acanthocephala mean? Spiny head What is the common name of the Nemertea? Ribbon worm What does Platyhelminth mean? Flat worm The lophotrochozoa grouping is based on more than simply comparative anatomy. What powerful biological measurement is instrumental in this grouping? DNA sequencing What is the common name of Brachiopods? Lamp shells...