Monday, March 5, 2007
- "Biology at Iowa university" 2006 http://www.biology.iastate.edu/Courses/201L/Annelida/%20AnnelINDX.htm
- "Phylum Annileda " 2004 http://www.esu.edu/~milewski/intro_biol_two/lab__12_annel_arthro/Annelida.html
- "A Hotlist of Annileda" 2006 http://www.kn.att.com/wired/fil/pages/listannelidama.html
- "Diffusion" http://www.blobs.org/science/diffusion/imgs/diffusion2.gif
- "Unsegmented Worms" http://sps.k12.ar.us/massengale/unsegmented_worm_notes_b1.htm
Monday, February 26, 2007
Platyhelminthes: Phylum that consists of simple animals with bilateral symmetry, mostly have a head; flatworms
Flatworm: simple animal with bilateral symmetry belonging to the phylum platyhelminthes
Nematoda: Phylum, with the simplest of animals, exhibiting a digestive system with two openings: a mouth and anus; roundworms
Roundworm: Pseudocoelomate animal that has a digestive system with two openings.
Pharynx: muscular tube used to suck food into the gastrovascular cavity.
Flat Body: Because of its flat shape, these unsegmented worms don't depend on respiratory systems; instead they can diffuse nutrients and essential gases along the body walls.
Flame Cells: some fresh-water flatworms contain flame cells, which help expel water from the body. The cells can join to form a network that empties through tiny pores in the animal's skin.
Nervous System/Brain: They have a definite head with a simple brain and developed nervous system.
-gather information from environment:
-find dark hiding places beneath stones and logs during the day(avoid predators)
Ocelli: some have 1/more pairs of eyes spots; detect whether animal is in light or darkness. Help sense surroundings, and obtain food.
Cells: Often scattered all over body; specialized cells sensitive to chemicals found in food, and others that can tell which way the water is flowing surrounding the animal.
Muscle Cells: allow to twist and turn; able to react to environmental conditions rapidly.
Simple nervous system: contains sense organs which detect chemicals given off by prey/hosts
Nerves(ganglia): transmit sensory information and control movement.
The phylum name is exactly what a flat worm is: platy- means flat and helminth means worm
Many flatworms are no more than a few millimeters thick, although they may be up to 20 meters long.
They are the simplest animals with a bilateral symmetry
Flatworms lack any kind of specialized circulatory or respiratory system. Because they are so flat they can depend on diffusion to transport oxygen and nutrients to their tissues.Many flatworms have one or more pairs of light sensitive organs called ocelli, or eyespots. These eyespots do not see objects as our eyes do but they simply detect whether the animal is in light or dark
- They have a more developed organ systems than either sponges or cnidarians.
- The flatworms are:
- Soft bodied
- Have a solid body form
- Are hermaphroditic
- Have spermatozoa with 2 tails
- Have a sack like gut
- Have epidermal cells that are multiciliated
- Have fiber form muscles
- And have neoblastsThus they stand distinct from all other major phylum of worms, the Annelida, whose members have a complete gut, segmented bodies with fluid- filled coelomic compartments, a cuticle- covered body wall, muscles that arise from epithelial mesodermal tissue, and monoflagellated sperm. Hermaphroditism, with reproductive organs as complicated as those of the flatworms, appear in the Gnathostomulida and Gastrotricha. The multiciliated epidermal cells (all worm phyla but the Gnathostomulida), the solid (acoelomate) bodies (Gastrotricha and miscellaneous representatives of Nematoda, Annelida, etc.), and fiber-form muscle cells.
Flatworms can live in almost any environment. Because of how they are they can adapt to any environment whether it is deep sea or small pond. Planarian worms are found in streams on the underside of rocks or leaves of water plants, if you were to watch their movement away from a source of light they would exhibit a negative response to light.
Sunday, February 25, 2007
The feeding habits of unsegmented worms vary depending on their classification as: free-living(planarians) or parasitic(flukes and tapeworms)
Free-living flatworms are variety eaters. They may be carnivores, feeding on tiny aquatic animals, or scavengers, feed on recently dead animals. Their main source for food is the water. They feed on sessile invertebrates, and can vary from, sea squirts, bryozoans, small worms, crustaceans. Some are even cannibalistic. They have a gastrovascular cavity with one opening at the end of a muscular tube called a pharynx(sucks food into the cavity) The enzymes in its intestines breaks down the food and the undigested material is expelled throat the mouth. Food enters and leaves the body of the worm through the mouth.
Parasitic flatworms thrive off of a host species, feeding on blood, tissue fluids, or pieces of cells. They depend entirely on their hosts to digest their food for them. Without a host, there would be no food, thus these organisms would die or go dormant.
Flukes generally alternate between different hosts during their life cycle. It has a mouth at its anterior end. A thick cuticle and 1/more suckers surround the mouth, which function by attaching to the host's internal body surface. Some species have a pharynx that pumps food into a pair off dead-end intestinal sacs, where it is then digested.
Tapeworms usually have two hosts, the adult worm lives in one kind of animal(main) and the larva lives in another(alternate). They have no digestive tract. Along its anterior side, a tapeworm has a scolex, surrounded by hooks and suckers which attach to the host's digestive system. It has no mouth or intestine, must live in the intestine of its host, where it can absorb molecules of food that the host digested. Main hosts; humans. Alternate hosts; animals( fish, cows, pigs, rabbits, etc.)
free-living roundworms are often carnivores, which catch and eat other small animals. Small algae, fungi, or pieces of decaying organic matter are a favourite of some soil-dwelling and aquatic forms. Others prefer to digest bacteria and fungi which act as decomposers.
Parasitic roundworms include those that live in the soil and attach to the root hairs of green plants. They suck out the plant juices and cause great damage, and are commonly found in tomato plants.
Saturday, February 24, 2007
Flukes, of the class Tremadota, undergo sexual reproduction and produce 10,000 to 100,000 more eggs than free-living flatworms. If they get to water, they hatch into swimming larvae, and infect a snail. They then infect a primary host, the human, by boring through the skin and eating their way through to the blood vessels. People infected with this disease often get very sick and die.
Free-living flatworms have a gastrovascular cavity with one opening at the end of a muscular tube called a pharynx (sucks food into the cavity). The cavity then forms an intestine with many branches along the entire length of the worm. Enzymes help break down the food into small particles, which are taken inside the cells of the intestinal wall, where digestion is completed. Because the intestine branches into nearly all parts of the body completed digested food can diffuse to other body tissues.
Some parasitic flatworms have a pharynx that pumps food into a pair of dead-end intestinal sacs where the food is digested. Their digestion is simpler than free-living worms, such as tapeworms, who do not have digestive tracts at all, but hooks/suckers with which they latch onto the intestinal wall of the host. They then absorb the food that passes by (already broken down by the host).
Roundworms however, have tube-shaped digestive tracts with openings at both ends, a very effective system. The anus is the opening in which any materials in the food that cannot be digested leave through.