Annelid Segmentation:

Transcription

1 Phylum Annelida Note: These links do not work. Use the links within the outline to access the mages in the popup windows. This text is the same as the scrolling text in the popup windows.. What is an annelid? (Page 1) Annelid Segmentation: The segmentation of most annelids is readily apparent. In this annelid, all of the segments look alike. An nternal partition, or wall, divides the segments from one another. Annelid Cross Section: n this segment from a preserved annelid, the coelom may be seen. It is a cavity lying between the body wall and the intestine. Annelid Phylogeny: This portion of the phylogenetic tree shows only the protostome line. other phyla in this line. Note the relationship of annelids to Annelid Cross Section: The tube within a tube structure can be studied in this diagram which is a cross section view of a single body segment. The outer tube (or body wall) consists of a thin outer cuticle, a skin (called the epidermis), and two ayers of muscle. Just inside of the body wall lies the coelom, a fluid-filled cavity lined with a thin tissue called the peritoneum. The peritoneum is derived from embryonic mesoderm. Thus this cavity is a true coelom, that is a cavity lined with mesodermal tissue. The innermost tube is the digestive tract, in this case a portion of the intestine. Note that the two major blood vessels of the worm are also located within the coelom The Coelom: This diagram gives a more 3-dimensional view of the coelom. Note that partitions segment the coelom nternally. The presence of a large body cavity allows more room for internal organs then in non-coelomate animals. This is a major evolutionary advantage of the coelom, seen for the first time in annelids. I. What are the kinds of annelids? (Page 2-4) Common Earthworm: Everyone is familiar with this annelid. Like most oligochaetes, its head is difficult to distinguish from its tail

2 and, except for size, all body segments are similar in appearance. Freshwater Oligochaetes: The majority of oligochaetes live in fresh water. Several types are shown in this drawing. Note that Tubifex s sessile, being partially encased in a tube.

3 Aquatic Oligochaete: This oligochaete has been photographed in its underwater home. The body wall of the worm is semiransparent, allowing the digestive tract to show through. It serves as an excellent illustration of the tubewithin-a-tube body plan. Video of Freshwater Oligochaete: This is a perfect example of a freshwater annelid that lives in a tube. ube. Watch as the worm emerges from its Terrestrial Oligochaete: The oligochaetes most familiar to us live on land and are collectively called earthworms. The animal shown here, although an earthworm is a different species from the common earthworm mentioned above. Burrow Tracks: Although they live on land, earthworms must keep their body surface moist. Thus they burrow into damp soil. This picture is a terrarium formed by two sheets of glass with a layer of soil 2 cm thick between. The errarium is 25 cm wide and 40 cm high. An experiment was performed in which 2 earthworms were tracked or 11 days. The green and red lines track the movement of the two worms during this time period. Note that both worms moved vertically from the soil surface to the bottom of the terrarium. They would probably have burrowed even more deeply in a larger terrarium. Earthworm in Burrow: This photograph shows a living earthworm within its burrow. he worm. An empty burrow is pointed out by the arrow. Note that the burrow is only slightly larger than Earthworm Setae: All oligochaetes have short bristles called setae protruding from the body wall. see two pairs of setae in each segment of this worm. If you look closely, you can Setae Magnified: This scanning electron micrograph of several earthworm segments shows the setae at a much higher magnification. Giant Earthworms: Several species of very large earthworms are found around the world. In North American, the giant Pacific

4 Worm is found in native forests along the western coast. The most famous giant earthworms occur in parts of Australia where one species reaches an average size of 2 cm in diameter and more than 3 meters in length. A somewhat smaller Australian earthworm is shown here in the large photograph. The giant worm on the right s from Ecuador, and the bluish one at the bottom is from Sri Lanka. Giant Brazilian Worm: This giant earthworm was photographed after being captured in the Brazilian jungle. These worms are said to be a food source for natives living in the Amazonian forests. Since the man in the picture is more than 5 feet all, we can estimate the surprising length of this worm. It must be at least 10 feet long! Earthworm Predators: Here we see two predators of the earthworm. The frog is just finishing its dinner, whereas the shrew has just begun. Shrews spend most of their life underground and usually capture earthworms in their burrows. Flatworm and Earthworm: Here, a large flatworm is in the process of attacking a small earthworm. o different phyla? Can you tell that these worms belong Polychaete on Sea Floor: The typical polychaete looks like the one shown here. Note the obvious segmentation and the thin paddleike structures protruding from each segment. This polychaete is crawling along the bottom of its shallow, salt-water home. Polychaete Among Rocks: Polychaetes are also common along rocky coastlines. of a rocky beach. This worm has been photographed in the shallow water Polychaete Cross Section: The paddle-like structures found on most body segments of polychaetes are called parapodia (the singular is parapodium). Note that setae protrude from the lower half of the parapodium. The setae of polychaete worms are longer and more numerous than those of oligochaetes. In this cross section through a body segment, the ube-within-a-tube body plan may again be seen. Polychaete Head: The head of polychaetes is distinct from the tail and bears various distinguishing features. In the worm shown here, 4 eyes are present as well as a pharynx bearing jaws. The pharynx is protruding in this picture, but can be retracted into the head when the jaws are not in use. Several short tentacles and a pair of fleshy palps are also visible.

5 Polychaete Life: A large number of polychaetes, including those described above and shown here, have a very active life style. They usually crawl or burrow on the ocean floor or in shallow waters along the coast, but most can also swim if necessary. Bottom Dwelling Polychaete: This sandworm is a good representative of the highly mobile polychaetes. combination of body undulations and action of the parapodia. It moves over the sand by a Preserved Polychaete: Here is a preserved sandworm in a dissecting tray. his worm! If our class had a laboratory, you would now be dissecting Large Polychaete: Most polychaetes range in size from a few millimeters to 20 centimeters long. eported to measure 72 cm in length. However, this specimen is Bristle Worms: The polychaetes shown here have exceptionally long setae extending from their parapodia. worm in the upper picture is crawling over a bed of coral. Note that the Bloodworms: These bloodworms have been dug up from their home in shallow salt water. Perhaps an angler will use them or bait as is often the case. The red color of these worms is due to the blood showing through their thin body wall. Do not confuse these polychaetes with midge larvae which are also called bloodworms although they are insects. Small, Swiming Ploychaete: There are many species of small polychaetes. One example is shown here. If you saw this animal in the water, could you identify it as an annelid? Would you know that it is a polychaete? Planktonic Ploychaete: t is rare for adult polychaetes to live primarily within the water column. However, a few small species do. The one shown here lives permanently among the ocean plankton.

6 Sea Mouse: The sea mouse is a odd looking polychaete that lives in both shallow and deep marine habitats. In the upper panels it is shown living on both a muddy and rocky surface. The top and sides of the sea mouse are covered with thin filaments and interspersed stiff bristles, sometimes called spines. To see the segmentation and parapodia, one must examine the under side of the sea mouse as shown in the bottom panel. Sea Mouse Flashing Colors: The most interesting feature of the sea mouse is its ability to change color. This is accomplished by the crystalline structure of the filaments and spines which can absorb light, then reflect it back as bands of blue and green. This flashing color may serve to deter predators. Lugworm: The lugworm is another polychaete often used by anglers as bait. It lives in shallow water where it burrows nto the mud or sand, forming a J-shaped tunnel. The lugworm shown here has been removed from its burrow. Its head (large end) occupies the blind end of the burrow and the tail points up toward the opening at he sand surface. Body contractions create a current of water into the burrow. Food collects at the blind end of the tunnel, near the mouth, while the water percolates out through the sand. Lugworm Castings: When the tide is out, the presence of lugworms can be detected by their castings on the sand, or mud, surface. About every 45 minutes, the lugworm needs to defecate. It crawls backward and defecates out through the opening of its burrow forming a pile of castings. Another indication of lugworms below is the presence of shallow depressions on the surface, such as indicated by the arrow. These depressions are formed over the blind end of the burrow as water percolates up to the surface. Amphitrite: Whereas the lugworm moves freely within its burrow and forms new burrows periodically, other sedentary polychaetes live most of their life confined within a single burrow. The type of polychaete shown here lives n a permanent, tight fitting burrow with its head just below the opening. It has tentacles that spread over the sandy surface, to search for food. The pink structures protruding into the water serve as gills. Diagram of Fan Worm: Fan worm is the common name for a large group of sessile polychaetes. All fan worms live in a permanent ube which they construct. The species shown here builds its tube from sand particles which it cements ogether by mucus secretions. The mouth of the worm lies at the tube opening. Long, feathery tentacles surround the mouth. As water flows over the tentacles, they collect small food particles and sand grains which are carried into the mouth. The food continues through the digestive tract, whereas sand grains are collected in a sac for future tube building. Fan Worm In Tube:

7 n this photograph of living fan worms, the nature of the sandy tube can be clearly seen. entacles fully extended, while another has retracted its tentacles into the tube. One worm has its Fan Worm Building a Tube: The worm in this video has left its tube and is starting to build a new one. grains to begin building a tube from the top down. Watch as the worm positions sand Fan Worm Slideshow: Fan worms are such beautiful animals, that we thought you would enjoy seeing more of them. This slide show illustrates several species photographed in various locations around the world. Can you see why these animals are sometimes called feather duster worms? Hard Tube Fan Worm: The so called hard tube worms are a group of fan worms that secrete calcium carbonate into their tube, making it much harder than tubes composed only of sand grains. Christmas Tree Worms: The Christmas tree worms are similar to fan worms, but construct their tubes by boring into coral. see two representative species with their spiral rows of tentacles extending from the coral surface. Here we Open and Closed Tubes: When fan worms contract into their tubes, they can seal the opening for additional protection as shown in the ight panel. Chaetopterus: The parchment worm is a unique polychaete. While not of any special importance, it is so unusual that we must say a few words about it. The specimen shown here has been removed from the U-shaped burrow in which it lives. Burrows are made in the shallow water of marine mud flats and lined with a parchment-like substance. They are open to the water at each end. As water is pumped though the burrow, food is extracted by a novel mechanism. Note that the body of this polychaete consists not of uniform segments, but of specialized regions in which groups of segments are fused to form unique structures. Only the rear half of the worm has well defined segments bearing parapodia. Chaetopterus Anatomy: This diagram shows the parchment worm within its burrow. Fan-like structures near the center of the worm move water through the burrow in the direction indicated by arrows. A pair of wing-like appendages control

8 he rate of water flow and secrete mucus. The mucus traps food particles and swells into a net due to pressure rom the water flow. A food cup eventually collects the mucus net containing trapped food and forms it into a ball which is then propelled forward to the mouth. If you go back to the photograph of a living parchment worm, you should be able to identify the fans, wings, food cup, and mouth. Leech: Leeches share many characteristics with the oligochaete worms, suggesting a close relationship between the wo groups. Both groups live almost exclusively in fresh water or moist regions on land. Externally, both are composed of repeated segments which lack parapodia, and there are few specialized structures in the head egion. Flattened Leech: Unlike the oligochaetes, which have a cylindrical body, leeches are flattened in the dorsal-ventral plane. This lattening makes it difficult for leeches to burrow and also restricts the size of their coelom internally. Leech Suckers: Leeches are unique among the annelids in bearing suckers. All leeches have a large posterior sucker for attaching to solid surfaces and a smaller anterior sucker that surrounds the mouth and aids in feeding as well as attachment. Aquatic Leech: Aquatic leeches are quite common in slow moving streams, ponds and lakes. attached to an underwater branch by its posterior sucker. The leech shown here is Medicinal Leech: Terrestrial leeches tend to be larger than aquatic species. This medicinal leech is at least 10 cm long. Giant Amazonian leeches are said to attain a length of 30 cm. Leeches in Mud: Like all terrestrial annelids, leeches must keep their body surface moist in order to absorb oxygen through the skin. In this example, two leeches are partially submerged in the mud. Hanging Leech: Most terrestrial leeches inhabit the tropics in regions where high humidity helps keep their bodies moist. often hang from vegetation in wait for potential prey. They II. How do annelids respire? (Page 5)

9 Earthworm Cross Section: The body surface of earthworms and leeches is covered by a thin, non-cellular cuticle. Oxygen must pass hrough both the cuticle and the skin to reach tiny blood vessels lying just beneath the surface. Mucus secretions to the surface of the cuticle help to keep it moist so that gases can pass through. Parapodia and Respiration: The upper lobe of each paradodium has a rich supply of blood vessels separated from the sea water by only by a thin membrane, thereby allowing for exchange of oxygen and carbon dioxide between blood and the aqueous environment. Tentacles as Gills: Fan worms such as those shown here exchange gases through their thin-walled tentacles. Polychaete Gills: Some sedentary polychaetes have anterior gill-like structures for respiration. The gills function similarly to the parapodia of active polychaetes. V. How do annelids move? (Page 6) Earthworm Cross Section: Use this diagram of an earthworm cross section to observe muscles within the body wall of the earthworm. The circular muscle layer is relatively thin. Its fibers encircle the body just beneath the epidermis. The thicke ayer of longitudinal muscle borders the coelom. The fibers within this muscle layer run lengthwise within the worms body. Earthworm Contractions: Observe the contractions and elongations in various parts of the body as this earthworm moves. Earthworm Locomotion: This diagram shows the cross section of an earthworm in its burrow. Press the buttons to see the worm change rom an extended, to relaxed, to bulged form. Note when each layer of muscles contract and how the setae make contact with the burrow. Then go back to the previous page and play the videos of a live earthworm crawling forward and backward. Earthworm Crawling:

10 Moving Backward: Polychaete Locomotion: The lower portions of parapodia can contact the surface over which a polychaete moves. Thus they are able either to provide traction or to propel the worm along by oar-like motions. This small polychaete can also back up, but prefers to turn around and move forward. Note that to swim fast, this worm makes one quick stroke with all of its parapodia, then holds them against the body and uses body undulations. Locomotion of a Large Polychaete: Rapid movement of the large, active polychaetes is achieved by serpentine wiggling motions as illustrated by his worm. Locomotion of a Leech: Leeches have a unique way of moving across a surface. Study this figure and accompanying video to understand inch worm locomotion style. Note how the leech searches for a spot to attach its anterior sucker before releasing the posterior sucker from its hold. Swimming Leech: Aquatic leeches are good swimmers. They propel themselves along by undulating the body in the dorsalventral plane. This is different from the serpentine movement of polychaetes which employs a side-to-side motion. V. How do annelids acquire and digest food? (Page 7) Earthworm Mouth: The earthworm s mouth is located at the tip of the anterior end as indicated by the arrow. As the worm burrows, it ingests soil, thus creating a tunnel as it crawls forward. Earthworms literally eat their way through he soil. Earthworm Digestive System: From the mouth, soil particles pass into a nearly spherical pharynx. The pharynx is muscular and its contractions help pull soil into the mouth. The earthworm digestive tract has a few specialized regions for handling its rough diet. The crop stores soil matter and the gizzard grinds it. Since the worm lacks teeth or aws, the gizzard uses sand and other hard particles of the soil to grind the organic matter more finely. This material then passes into the tubular intestine where nutrients are absorbed through the intestinal wall into the blood stream. Note that the intestine is very long and constitutes the major part of the digestive system. Cross Section Through Intestine:

11 This cross section through the earthworm s body is a photograph taken through a microscope. It is what you would see if this course included a laboratory. The intestine is a tubular structure suspended in the coelomic cavity. Food passes through the intestinal lumen and is absorbed through the intestinal wall. Note that the ntestinal wall is folded inward at the top. This almost doubles the area for nutrient absorption. Earthworm Anus and Castings: Although the anterior and posterior ends of oligochaete worms look alike, the anterior end is usually more pointed. Note the location of the anus in this earthworm. When ingested soil reaches the end of the intestine, t is eliminated through the anus forming a casting at the opening of the burrow. Polychaete Jaws: Many of the active polychaetes are predators and utilize jaws to capture and kill their prey. As can be seen in his living clamworm, the jaws are attached to the muscular pharynx. In this worm, the pharynx has been extruded through the mouth and the jaws are in position for hunting. The right panel shows a pair of jaws have been removed from the worm and enlarged to show their serrated edges. This worm can deliver a mean bite! Fan Worm Feeding: A filter feeding fan worm is shown here. The small filaments on the tentacles bear cilia and create a flow of water over tentacle. Tiny food organisms in the water stick to the filaments and are carried to a small groove hat runs down the center of the tentacle. Watch as food particles are moved along the groove to the mouth which is positioned at the base of the tentacles. Leeches Attacking Earthworms: Leeches can be fearsome predators of other invertebrates, including earthworms as shown here. The leeches are sucking all bodily fluids from the worm and will eventually consume the dehydrated carcass. Leeches Sucking Blood: The parasitic style of leeches is well known. In this picture, several leeches have attached to an unlucky human and are sucking blood. The leeches are tightly attached by both anterior and posterior suckers. Note human blood seeping from around an anterior sucker at the arrow. Aquatic Parasitic Leeches: Aquatic leeches often parasitize fish as shown in the left panel. Too many leeches per fish can kill the host as may be occurring here. Humans that wade or swim in fresh water may also attract leeches. What child has no ound a leech while at summer camp? Leeches Parasitizing a Frog:

12 Leeches can also parasitize frogs and can even kill them as has happened here. Leeches Parasitizing a Frog: n this example of bird parasitization, leeches have entered the sinus cavity of a duck as ascertained by wildlif agents during an autopsy. Terrestrial Leech: This Tiger leech is attached to a leaf overlooking a spot where a mammal may wander by. The anterior end of the leech is equipped with temperature receptors, sensitive to mammalian body heat. The leech is stretching outward in an attempt to locate a host. Perhaps it senses the photographer! Attached Leeches: These leeches have attached to human skin using their anterior suckers. Oral Sucker and Jaws: The edges of three jaws can be clearly seen within the mouth of this leech. The right panel is the magnified mage of a single jaw. Note the tiny, sharp teeth extending from the jaw s edge. Leech Feeding on Blood: This leech has completed its incision through human skin and is feeding on the blood seeping from the wound. Often the victim is unaware of the attack as the leech secretes a local anesthetic that numbs the area. The blood is kept freely flowing by an anti-coagulant called hirudin that is secreted from the leeches salivary glands. Leech Digestive System: The leech digestive tract consists mainly of a large crop. Blood that has been sucked into the pharynx enters he crop for storage. Outpocketings of the crop, called cecae, greatly increase its storage capacity. As the crop fills with blood, the body of the leech expands. Indeed, a leech can consume more than ten times its own weight as blood at a single meal. Having done so, the leech can go for months before requiring more food. Since blood is a liquid and easy to digest, the intestine of the leech is quite short. It digests and absorbs the stored blood slowly, a process that can take up to 100 days. VI. What type of circulatory system do annelids have? (Page 8) Earthworm Circulatory System: Note the location of the two major blood vessels in the earthworm. The dorsal vessel lies just above the

13 digestive tract and carries blood toward the head. The ventral vessel is suspended just below the digestive ract and carries blood in the opposite direction. These two vessels are directly connected in the anterior region by pairs of blood vessels that encircle the esophagus. These vessels along with part of the dorsal blood vessel contract rhythmically to pump blood into the ventral blood vessel and through the body. Behind these contracting hearts, branches of the dorsal and ventral vessels form capillary beds within the wall of the digestive tract in each segment of the worm. This allows nutrients from the intestine to diffuse into the bloodstream. VII. How do annelids excrete wastes? (Page 9) Earthworm Excretory System: The metanephridia are tubular organs that are found in pairs in most segments of the worm s body. They lie along the sides of the digestive tract within the coelom. Structure of Metanephridium: Study the metanephridium which is light yellow in this diagram. One of its ends opens into the coelom where t collects coelomic fluid. Curiously, the tubule of the metanephridium then passes through the segmental partition into the segment just posterior. Most of the tubule lies within this segment. Note the bed of small blood vessels that are intertwined with the tubule. Some exchange of materials between urine and the blood occurs here. The tubule empties to the exterior through a tiny pore in the body wall. Ragworm: The ragworm lives in estuaries and is often most abundant in areas where the salt concentration is most variable. This marine worm can even live in fresh water if calcium levels are sufficient. Experiments have shown that the ragworm can keep the concentration of its coelomic fluid almost constant as it is moved from normal to highly diluted sea water. This is due to its ability to produce urine that is less concentrated than the coelomic fluid. Hence excess water can be excreted while salts are absorbed back into the bloodstream. VIII. What type of nervous system do annelids have? (Page 10) Earthworm Nervous System: The basic nervous system of annelids can be illustrated in the earthworm. A double cerebral ganglion lies above the pharynx and another large ganglion lies below. These ganglia are connected via a nerve around each side of the pharynx. The subpharyngeal ganglion connects to the ventral nerve cord which runs down he length of the body beneath the digestive tract. Note the swellings of the nerve cord in each segment. These are the segmental ganglia and they have primary control over locomotion. In fact, the worm can crawl and burrow even if its brains are removed. Annelid Eyes: Note the simple eyes on the head of this polychaete. There are four eyespots present, two on each side. Leeches have one pair of simple eyes, as can be seen in the photograph. Note also the tentacles of the polychaete which bear a variety of tactile and chemosensory cells.

14 X. How do annelids reproduce? (Page 11)

15 Earthworms Mating: The two worms here are mating. They have secreted a sticky slime that temporarily binds them together and provides a medium through which sperm can travel. Anatomy of Earthworm Mating: While the worms are bound together, sperm passes from its storage site in the seminal vesicles, travels along an external groove in the body, and enters the seminal receptacle of the partner worm. Release of Eggs and Sperm: As the slime tube moves anteriorly, eggs are released. When the slime tube progresses a bit farther, the partner s sperm are released from the seminal vesicle. It is curious that earthworms copulate and transfer sperm o the body of another individual, yet fertilization does not occur inside the animal. The two kinds of gametes are kept separate until they pass into the cocoon, and it is there, outside the worm's body, that fertilization akes place. Earthworm Cocoons: Cocoons of earthworms are shown here at several magnifications. earthworm. Those at the bottom are from the giant Embryos in Cocoon: The fertilized eggs within the cocoon develop into young earthworms which break out to begin life in the soil. Earthworms Mating: Play this interactive animation for a good summary of earthworm copulation, fertilization and cocoon ormtion. Trochophore Larva: The trochophore larva is diamond-shaped and has a band of cilia around the middle and an apical tuft of cilia on both the top and bottom ends. Its only conspicuous internal feature is a gut opening into a lateral mouth and an anus on the bottom. Polychaete Larva: This larval stage of a fan worm swims by beating cilia, although it is shaped somewhat differently than the classic trochophore.

16 Paolo Worm: The Paolo worm lives in the oceans of the south pacific. When it is time to reproduce, the epitoke breaks off, swims to the surface, and discharges large amounts of eggs or sperm (remember that the sexes are separate in polychaetes). The anterior end of the worm (the atoke) survives and regenerates the missing part. Polychaetes Swarming: At the time of reproduction, so many worms come to the surface to reproduce that the area is thick with them. n fact native islanders sometimes row out and collect the worms for a feast. In the magnified image on the ight, the head and trunk of this worm can be distinguished from the posterior segments which contain the gonads. Leech with Cocoons: This leech has attached its cocoons to the ventral body surface. When the cocoons hatch, the young leeches will attach to the adult and remain protected until old enough to live independently. X. Are annelids important to humans? (Page 12) The Earthworm Handbook: t seems that farmers are aware of the value of earthworms. A single worm passes its own body weight of soil hrough its intestines every 24 hours. When a moderate number of worms are present, topsoil is formed at the ate of 2 inches every 10 years. Earthworm Numbers: Farming practices and the type of crop grown determines how many earthworms live in the soil. Plowing decreases earthworm numbers, whereas addition of manure increases them. A fertilized pasture can support as many as 5 million worms per acre. Darwin and Aristotle: Darwin showed that earthworms aerate the soil through their burrowing. They drag leaves and other organic matter from the surface into the soil, closer to the roots of plants. They bring nutrients such as phosphorus and potassium into the topsoil from deeper layers. Darwin estimated that tons of dry earth passes through he intestines of earthworms each year for each acre of soil. Although Aristotle recognized the importance of earthworms and called them the "intestines of the soil", that knowledge, like so much other scientific understanding was suppressed by the ignorance of the dark ages. Even Darwin's contemporaries believed earthworms to be harmful to cultivated plants until publication of his monograph. Later work has supported Darwin's findings on the ecology of earthworms. Forest Earthworms:

17 The native earthworms in most of the Northern United States and Canada were eradicated during the last ice age, 15,000 years ago, thus today s Northern forests were formed in the absence earthworms. In the native orest environment, the introduced European earthworm destroys much of the ground cover and kills young ree seedlings which may eventually result in fewer mature trees. Fisherman are adding more worms to the area by dumping unused bait. Sea Mouse Spines: The sea mouse, shown on the left, has become famous for its unusual hair and spine-like structures that collect and channel light with almost 100 per cent efficiency. This exceeds the ability of man made optical fibers. Optical engineers hope to produce better products by using the molecular structure of sea mouse spines as a model. The Medicinal Leech: As late as the 19 th century, it was believed that bodily disorders were caused by an excess of bad blood. The medicinal leech (as shown here) was attached to patients to relieve them of this surplus blood. Indeed, it s now thought that George Washington's death may have been hastened by loss of blood from extended reatment with leeches. Leeches in the News: Leeches do have some medical value if used appropriately. They can be utilized to remove blood that is rapped in an otherwise inaccessible spot, as shown here beneath an injured toe nail. Reattached Thumb Story: Leeches are also used to relieve congestion by pooled or congealed blood in microsurgically replaced fingers and toes, until such time as new veins form to drain away the excess blood. Such usage is documented by hese pictures. Clockwise from the upper left: thumb tip newly replaced after having been cut off by a saw accident, leech being applied to consume blood at site of replacement, leech at work (see arrow), and happy patient recovering.