Reference

- Miller, Kenneth R. and Joseph Levine. Biology. 4th ed. Upper Sadle River, NJ: Prentice Hall, 1998.
- "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

Useful Vocab

Unsegmented Worm: worm whose body is not divided into special segments; flatworms and roundworms.
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.

Adaptations to the Environment

Flatworms:
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:
-locate food
-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.

Roundworms:
Simple nervous system: contains sense organs which detect chemicals given off by prey/hosts
Nerves(ganglia): transmit sensory information and control movement.

Useful Links

http://userwww.sfsu.edu/~biol240/labs/lab_17hydrostaticsk/pages/planaria.html

http://userwww.sfsu.edu/~biol240/labs/lab_17hydrostaticsk/pages/flatworms.html

http://devbio.umesci.maine.edu/styler/globalworming/platyhelm.htm

http://www.waterwereld.nu/images/flatworm.gif

Interesting facts

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

Comparison to other phyla

- 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 neoblasts

Thus 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.

Movement

Free-living flatworms usually use two means of locomotion at once. The Cilia on their epidermal cells help them glide through the water and over the bottom. Muscle cells controlled by the nervous system allow them to twist and turn so that they are able to react to environmental conditions rapidly. The flatworm glides along over even surfaces on its ventral ciliated surface. It does this by using its muscle layer against something that the cilia can push against. The flatworm is also capable of crawling over or around an obstacle by using its muscular undulations

Response to the environment

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.

Respiration

Unsegmented worms have no true respiratory system, however they do take in oxygen. They respire through diffusion; gas exchange occurs on its outer surface. With this process, the flat shape of the worm's body is necessary so that no cell can be too far from the outside.

Feeding

The feeding habits of unsegmented worms vary depending on their classification as: free-living(planarians) or parasitic(flukes and tapeworms)

Flatworms
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.)



Roundworms
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.

Reproduction

Free-living flatworms can reproduce either sexually or asexually. Most are hermaphrodites (both male and female organs). During sexual reproduction, the worms join in pairs and share sperm. The eggs, which are laid in small clusters, hatch in a few weeks. Asexual reproduction by fission is also common, with their incredible regenerative skills. Parasitic flatworms do not produce asexually, but sexually.
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.

Roundworms reproduce sexually, and most species have separate female and males, with some rare hermaphroditic species. The fertilization happens in the female body. 2 or 3 hosts may be involved in the life cycle of some roundworms.

Excretion

Flatworms can get rid of carbon dioxide and other wastes by allowing them to diffuse out of their body walls. Freshwater flatworms (i.e. Planarians) have flame cells, structures which get rid of extra water by joining many cells together to from a network that empties through tiny pores in the animal’s skin. Flame cells function like a kidney, removing waste materials. They get their name from the beating of the cilia on them, resembling a flame. The inner surface of the cell is coated in flagella. The beating of the cilia and flagella help move liquid through the cell.

Like flatworms, roundworms also allow diffusion to accomplish their excretion.

Circulation and Internal Transport

Flatworms depend on diffusion to transport oxygen and nutrients to their tissues, as they lack any kind of specialized circulatory or respiratory system.

Digestion

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.

Structure

Annelids are Coelomates (have a body cavity surrounded by mesoderm) and are triploblastic (has three Germ layers; Ectoderm, Mesoderm, Endoderm). They are also closed circulatory system with no segmentation.

Introduction

When one thinks of unsegmented worms (Annelids), one thinks of blood-sucking leeches, parasitic tapeworms, and dirt eating earthworms. In reality, there are over 15,000 known species, and can be found in the sea and in the earth. They can be as small as the dirt in your nails or or as tall as a basketball hoop, and have been used for several centuries by humans. We'll show you everything you need to know about Annelids in the following little posts.