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Midterm

3229G Midterm: 3229 midterm review

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Department
Biology
Course Code
Biology 3229F/G
Professor
Graeme Taylor

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Description
3229 midterm review Cnidarians Simple basal organisms Feed on zooplankton and other small organisms Some are bright green, so one would think it is a plant. Many of these organisms’ house photosynthetic algae Some of them are stuck to rock, but not permanently Sands at your feet are made by cnidarians. Corals belong to this group In the coral folds, algae live there. There are two types of coral – can and can’t form the skeleton Corals belong to the group metridium. They have two types of skeletons, calcium carbonate, and hydrostatic If going to be colonial, each polyp is connected by the gastric system. They catch prey at night (zooplankton) and can share food with other individuals in the colony What is a cnidarian? 1. Diploblastic Metazoa with ectoderm and endoderm separated by an (primarily) ectodermally derived acellular mesoglea or partly cellular mesenchyme The bioplan is polymorphic. Consider one form the polyp form and the medusa form. It has two dark lines – outer line is the epidermis, inner line is the gastrodermis. Third tissue layer is the mesoderm. It arises after gastrodation. The third tissue layer is a more derived tissue layer Mesoglea is not a tissue layer. A tissue layer must be connected together in a way. They sit on a basal lamina. Mesoglea is a bunch of loose cells. It has a gut in it’s design. The mouth is also the anus. Medusa form has the same pattern as the polyp form 2. Possess primary radial symmetry, often modified as biradial, quadriradial, or other variations on the radial theme; the primary body axis is oral-aboral (mouth is butt) They are circular in design. Most animals are bilateral in design. They have a radial theme. They have a body axis. They have an oral-aboral axis 3. Exhibit alternation of asexual polypoid and sexual medusoid generations; but there are many variations on this basic theme (e.g. a medusoid stage is absent in the class Anthozoa) 4. The endidermally derived gastrivascular cavity (coelenteron) is the only “body cavity”. The coelenteron is saclike, partitioned, or branched, but has only a single opening, which serves as both mouth and anus 5. Nervous system is a simple nerve net(s), composed of naked and largely nonpolar neurons 6. Typically have planula larvae (ciliated, motile, gastrula larvae It has a cavity. Has a jelly-like characteristic. Have separate sexes. The egg gives rise to planula larvae that is motile. They need some way of dispersal 7. Musculature formed largely of myoepithelial cells (epitheliomuscular cells), derived from ectoderm and endoderm (adult epidermis and gastrodermis) Novel trait, we are using as a synapomorphy. Derived from epithelial tissue. Will see longitudinal and circular muscle tissue in this group 8. Possess unique stinging or adhesive structures called cnidae; each cnidae resides in and is produced by one cell, the cnidocyte. The most common cnidae are called nematocysts Stinging cells is key evolutionary trait. Will see in all groups. Cells are complex with a thread/harpoon in them. Cen be mechanically/chemically induced. The idea is to penetrate predator/threat to jellyfish. Used for feeding as well, a way to break shell of various things (plankton, etc.). Releasing some poison in the process. Has a complex structure to it. Little barb and a thread there Phylum Cnidaria Subphylum Anthozoa Class Anthozoa Subphylum Medusozoa Class Scyphozoa Class Cubozoa Class Hydrozoa Defining characterisitcs of the Anthozoan - All marine - 6000 species - Solitary or colonial polypoid - Medusa stage is absent - Thick and well developed column They are all marine. Not only are they the most ancestral, they are the most successful. If you do genetic analysis on this group, you would place it in the hydrozoans. - No operculum and cnidocil - Circular mitochondrial DNA - Ciliated siphonoglyph - Mesenteries/septa in coelenteron Other parts have linear DNA - Anthozoan - Order Scleractinia – true corals - Largest taxon 3600 species - Calcium carbonate skeleton - Majority are colonial - Small polyps 1-3 mm diameter - 100,000 polyps - Reef builders (hermatypic) have zooxanthellae Largest group within that. The corals in the group are relatively derived. The majority of them are colonial. A head or coral head, could have up to 100 polyps. Come in all different forms. They are reef builders. Ahermatypic don’t have the skeletons Order PennatulaceaI –Sea pens and sea pansies - Bilateral symmetric - A single, long axial polyp with smaller polyps on side branches - Anchor in soft bottoms - Broad surface into current A multitude of different polyps. Bilateral in design - Gametes produced directly by the polyp stage - Planula larvae develops from fertilized egg - Feed on phytoplankton and other microscopic food particles Do produce gametes. If medusa stage is missing, gametes form polyp stage Asexual reproduction in Anthozoan - Longitudinal or transverse fission - Pedal laceration - Fragmentation in corals They can rip themselves in half and not bleed to death as they don’t have a circulatory system. They can reproduce by leaving behind a foot. The foot will grow into another body. If a piece of coral fragments from colony, it can potentially form another colony Anthozoan >Acontia: thin filaments in the coelenteron - Loaded with nematocysts and secretory cells - Can be extended outside the body through small pores in the body wall - Defend and attach - Digestion Competing with each other for substrate. They will produce thick filaments (acontia - can come out of side and mouth). Will burn other anemone Origins of the class Anthozoa They are the most primitive in the group even though they are the most successful. Have good fossils of them. Second biota discovered. Fossils make a good example of what was going on at the time. Can see the Anthozoan is almost like it was 5-6 m.y.a as it is today. Phylum Cnidaria – Hydrozoa - Most marine - Shallow and deep water - Mesoglea thick but lack cells - Gastrodermis lacks cnidocytes - Gonads epidermal - Small medusa - Velum - Polyp more complex. Has a little skirt around the bell The complex life history of hydrozoans > Specialization of the polyp stage - Adult female - Egg and sperm - Zygote Show the most variation in terms of a complex life cycle. Can have specialization in polyp stage. Freshwater bodies aren’t as deep, so they don’t have a whole pile of zooplankton to eat, so there is no real need for a medusa stage. >Specialization in the medusa stage - free swimming actinula larvae Can have an alternative where something has driven the group to have to do something with the benthos. Hairy planula larvae has cavity in it and gives rise to another larvae form (no polyp stage here). The medusa and polyp stage Life history involves a tiny little polyp. Adult is doing the feed but it is still there. Medusoid Locomotion - Epidermal musculature developed for swimming (bell area) - Sheets under the bell - Partially embedded in mesoglea Mesoglea acts as an internal skeleton. Hydrostatic skeleton – if closes its mouth, it can be rigid. The form is considered a hydrostatic skeleton. We use our hydrostatic skeleton when we are constipated. Mesoglea is another skeleton - Circular muscle contracts - Incompressibility of water - Water is forced out of the bell from the force of contraction - Jelly is propelled in the opposite direction This also helps in the mobility. Phylum Cnidaria – Class Scyphozoa Around the edge of the medusa are compound sensory organs known as rhopalia Rhopalia – sensory structure. Not cephalized (has brain in anterior section). Neurons are concentrated around rhopalia Rhopalia houses a multitude of sensory things. Pigments are able to detect light. Statocyst – able to detect gravitational field. Will want to go to the darkness (bottom) when no light. Go to the top when light out - No velum - Gastric tentacles Gastric tentacle – why inside gut? It helps with digestion. Must grab with tentacle. Will pull in but won’t be able to chew. They have cnidocytes on the tentacles The gonads of a scyphozoan develop from endoderm Lifecycle of Pelagia noctiluca Exists in the pelagic environment in its entirety. Give rise to broadcast spawning (group sex: release gametes at once in one area). Have development to get into a multicellular state Aurelia Lifecycle It has a polyp stage. It’s going to have broadcast spawning. It will find a cave and metamorphose (rearrangement of cells) to turn into a polyp. Gives rise to ephyra larvae Cubozoa - The medusa of a cubozoan is four sided (box-like) and there are either single tentacles. Or a cluster of tentacles, based at each corner of the box. A key difference between the Cubozoa and other Scyphozoa is the presence of a Velum in the medusa At the base of the bell, there may be a singular or a cluster of tentacles. They do have this bell. But most prior to this, given all the characteristics, they would be included in the scyphozoans They are small in size but they are super active and will hunt prey down. Quite toxic (sting). If we look closely at the rhopalium, it has a complex eye. Some people say it can actually resolve and image. - A short-lived polyp phase - The cubozoan polyp does not stobilate (form of asexual reproduction) - It buds off a single medusa and then dies The cubozoan is known as “the sea wasp” The “sting” from its nematocysts is sufficiently painful that beaches may be closed when Chironex is present in large numbers. Nematoda Nematodes can be in the sea, freshwater, and terrestrial environments Female is distinct from male How abundant are they? - 1 million/meter freshwater benthos - 4 million/meter – marine benthos Often occur in abundance. As soon as an apple falls to the ground, it rapidly becomes infected by nematodes (must see with microscope, most are small). Many of them in fresh/sea water. Nematodes have lips. Annelid worms have circles on it Nematoda have tapering at both ends. They are distinctly round without segmentation. Most nematodes are tiny, except parasitic ones Pig guts can be full of Ascaris, which is why some religions ban pork Nematodes are really small organisms. Eggs are really resistant. Can survive for years Microfilaria – potentially live on surface of skin. Swim around in any fluid in the body. Tiny and parasitic. Mosquitoes will also transmit them Described Species - 16,000 - Estimated 100,000 to millions Bioplan of the Phylum Nematoda - Morphology homogenous - ‘worm’ form >long and tapered at both ends - Bilaterally symmetrical > except anterior region - Mouth terminal – with lips 6 or 3 - Tissue cellular or syncytial (cells swimming amongst each other. Like mesoglea. Soup of tissues) - Species specific number of cells (eutely) - Mostly no cilia - Some have ciliated gastrodermal cells They have two little pockets at side of head (thought to be sensory) Phylum Nematoda: Musculature, Internal Pressure, and Locomotion Nematode locomotion on a solid surface: - Alternating contraction - Sinusoidal waves When the move, they move like a tiny whip as they have longitudinal muscles. They have circular muscles. They require some substrate to push on. They require some traction Longitudinal and circumferential arrangement of fibres. Cannot allow mobility since fibres do not extend They have this mesh-work cuticle layer. Associated with the arthropods. Muscles work against the hydrostatic skeleton. This allows the cylindrical object to remain stiff and flexible A spiral arrangement of fibres allows length and diameter change without change in volume. Mesh has angle design. Allows this structure to experience pressure without breaking. Can expand and contract. Don’t want it to be able to flex Much of the success of nematodes as parasites in harsh environments is due to the protective cuticle Layers (outside -> inside): External cortical Layer -> Homogenous Layer -> 3 Fibrous Layers -> Basal Lamina Eggs hatch as small nematodes - The larvae pass through four molt stage as they develop to the adult form It sheds its exoskeleton to extend its length. Their cuticle offers little protection and water loss, so you will find them in moist environments. They call the in-between molts larvae The epidermis is arranged in four fields Reason the nematode is round is because it exists under pressure. It has a true hydrostatic skeleton. 4 groups of longitudinal muscles. Muscles connects to the nerve instead of nerve activating the muscle. Don’t have a peritoneum. Organs are floating around Phylum Nematoda The myoneural system of nematodes is unusual. Rather than motor neurons running from the nerve cord to the muscles, each muscle cell extends a process to the nerve cord Nematodes have a high internal fluid pressure (70mm Hg in Ascaris and between 16-225mm Hg in other nematodes). Many nematodes are very small and they don’t have a coelom at all. Acoelom (no coelom) Phylum Nematoda The high internal pressure tends to collapse the gut. The pharynx acts as a muscular pump concentrating food and forcing it back into the gut. The pharynx opens, draws in food, concentrates the food into a bolus which is moved back and though a valve into the intestines Molts involve the cuticle and all cuticle lines structures. This means that the: Pharynx Rectum Excretory pore Vulva Stylets Are shed and replaced at each molt Some nematodes hatch and molt within the egg – this means they hatch as second stage larvae Some molts may take place in rapid succession so that the old cuticle is still present Adults may molt several times during their lives but do not grow at such Reproduction Most nematodes are dioecious Syngamy (cross fertilization) occurs in most species Some are hermaphrodite, few are parthenogenetic (offspring develop from unfertilized eggs). Some cross fertilization occurs Reproductive system of a female nematode Can develop 25k eggs in a day. The vagina is along the body, near the anus - The oviduct shapes the egg. Part of the oviduct may be modified as a seminal receptacle. - The uterus stores fertilized eggs prior to laying - In many species the uterus secretes the outer covering of the eggs Male reproductive system Spicule – ability to grasp female. Either in the free body and are attracted to the female -Some male nematodes have a copulatory bursa, as well as spicules, to grip the female during copulation. Attracted by pheromones Males approach females with their heads towards the female opening (suggesting attraction to a pheromone) and then turn to bring the reproductive openings together - Fertilization (in the oviduct of the female) is followed by egg shell development. [In some parthenogenetic species, “fertilization” triggers the completion of egg development and no nucleus fusion takes place] -Newly hatched nematodes often have a stylet that is used to cut a slit in the protective shell to allow the escape of the larva. -Egg hatching in parasitic forms is triggered by host conditions, e.g. gut temperature or pH, exidates of growing plant roots. In fee living forms, environmental stimuli – temperature, moisture, O 2evel Annelida Annelids
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