Adenophorea

(Roundworms)

Phylum Nematoda

Class Adenophorea

Number of families 96

Thumbnail description
Primarily free-living marine, freshwater, and terrestrial nematodes; considered to be the most primitive form of nematodes

Evolution and systematics

Nematoda, the phylum above the class Adenophorea, have left very few fossil remains. The earliest fossils that contained nematode remnants were found in Eocene strata (the era from about 55–38 million years ago). More authenticated fossils are of nematodes preserved in amber, such as those from fossilized shark muscles and mammals frozen in permafrost. The fossil record is too fragmented to explain much about nematode origins, and conclusions about nematode phylogeny have been mostly based on observations of living species. It is hypothesized that nematodes originated during the Precambrian era, what was the Proterozoic period (about one billion years ago).

As of 1994, about 20,000 species of nematodes have been described, with an estimate by various researchers of the total number of nematode species living on the planet at 80,000–1,000,000. This phylum is considered to have the lowest number of yet-to-be-described species of any animal. Hyman divided nematodes into 17 orders, whereas Chitwood separated them into two main classes, Aphasmidia (now Adenophorea) and Phasmidia (now Secernentea). Controversies still exist, but for the most part, many scientists such as A.R. Maggenti, who helped to develop the classifications, treat nematodes as a separate phylum with two classes, Adenophorea and Secernentea, which were divided based on molecular and morphological characteristics. These two classes are primarily separated (along with other important criteria) with respect to whether they do not possess phasmids (as in Adenophorea) or do possess phasmids (as in Secernentea). Two subclasses are recognized: Enoplia and Chromadoria. In addition, there are 11 orders and approximately 96 families. The total number of species of adenophoreans is estimated at about 12,000 worldwide. Scientific surveys of seabed mud, along with other reliable evidence, suggest that a great number of species are yet-to-be discovered.

Physical characteristics

The majority of adenophoreans are free-living, microbotrophic, and aquatic nematodes. Only a few species are plant parasitic, invertebrate parasites, or vertebrate parasites. They range in size from microscopic to as long as 3.25 ft (1 m) in exceptional cases. Adenophoreans are considered non-segmented pseudocoelomates; that is, creatures possessing a three-tissuelayered body that has a fluid-filled body cavity (pseudocoelom) between the endoderm and the mesoderm (the innermost and middle tissue layers).

A flexible but durable collagenous cuticle protects the body with a series of grooves across the body from head to tail. The non-cellular cuticle, which generally has a smooth surface, can sometimes contain transverse or longitudinal striations and has four layers: endocuticle, epicuticle, exocuticle, and mesocuticle. The cellular hypodermis is the subcuticular layer that secretes the cuticle. Phasmids—which are minute pore-like chemoreceptors that (when present) are usually paired—are generally absent from adenophoreans. Their sensory system contains well-developed amphid apertures, which are postlabial (past the lips) in position, with some species having apertures that are labial (on the lips). The apertures are variable

in external shape, being sometimes circular, pocketlike, pore-like, or spiral.

Somatic and cephalic setae, which are elongated structures joined with the cuticle, are common. These tactile sensory organs are usually located around the oral openings. The cephalic sensory organs, which number 16, are setiform to papilloid, and post-labial or labial in position about the head. Deirids, which are paired, porelike organs located in the lateral fields near the nerve ring, are present in some species.

Usually present, hypodermal glands are a thin tissue layer beneath the cuticle that thickens to make the dorsal, lateral, and ventral chords and extend the body's length. In general, they are tactile sensory organs usually located around the oral openings. They contain uninucleate hypodermal cells. A layer of longitudinal muscles underlies the hypodermis.

Bursae (or caudal alae) are rarely found. The ventrally located excretory system, when present, is usually single-celled, usually with non-cuticularized terminal ducts, and lacking collecting tubules. A rectal gland is usually absent. When present, there are three caudal glands located near the posterior region. The muscular esophagus or pharynx (the tube that moves food from the mouth/head to the stomach/intestine) varies in configuration, but the majority of adenophoreans have three esophageal glands: two that are subventral and one that is dorsal. The subventral glands open into the posterior metacarpus. The dorsal gland opens anteriorly into the procorpus or the anterior metacarpus. Its basic structure is corpus (the anterior part is cylindrical) with the basal (bottom) region sometimes swollen in the shape of a bulb. The glands empty their contents into the esophagus to aid in digestion. The tail is the region between the anus and the posterior tip. The male tail is smooth, and lateral cuticular caudal extensions of the tail rarely occur.

Distribution

Adenophoreans are found worldwide, especially in water-filled areas around vegetation and in soils, on plants, and in animals.

Habitat

Adenophoreans are commonly found in most kinds of habitat (except for desert regions) throughout the world, particularly in marine sediments. They inhabit a wide variety of habitats, including both water and soil.

Behavior

Their behavior is classified as being usually free living, but with some species behaving as parasites.

Feeding ecology and diet

The free-living species are predators, carnivores, herbivores, and omnivores, feeding mostly on bacteria, fungi, and soil organisms. The parasitic species feed on nutrients (such as blood, body fluid, intestinal contents, mucus) found within their hosts. Adenophorean worms generally have some form of stylet, a hard, sharp spear, which is used for feeding. Muscles move the stylet in and out, allowing the worms to puncture cells. Once opened, the worm will empty the contents of the cell.

Reproductive biology

Male adenophoreans sometimes have thin cuticle extensions on both sides of the anus called bursae, which are fluid-filled body sacs. When present, bursae are used to hold females during copulation. Male testes, when present, are two in number and are shaped similar to the female ovary. The spicules, the male copulatory organ, are paired. Males have a single, ventral series of papilloid or tabloid pre-anal supplements. Sperm accumulate in the seminal vesicle and exit through the anus. During mating, the rigid spicules insert into the vagina and form a passageway for the sperm. The female ovary contains germ cells that produce eggs. Fertilization, mostly initiated by male sperm, takes place in the uterus, with eggs released through the vagina. (Most species produce males and females, but some species only produce hermaphrodites, in which both male and female structures are contained in the same individual.) Most eggs are about the same size and shape.

Conservation status

No adenophoreans are listed on the 2002 IUCN Red List. They are found worldwide and frequently occur in very great densities.

Significance to humans

Living free and as parasites of animals, insects, and plants, adenophoreans constitute an important part of nature and to the activities of humans. As crops are cultivated to feed the world's population, adenophoreans become more numerous as they feed on agricultural plants. Parasitic adenophoreans cause yield losses by themselves or they may join with other organisms such as viruses, fungi, and bacteria to advance disease development in plants. They also cause loss of nutrients and water in the plant, thus increasing the plant's susceptibility to other dangers. Adenophoreans, when infecting a human, can cause various diseases, and in some circumstances, death to the human host. On the other hand, studies have shown that the appearance of adenophoreans is a good indicator of biodiversity, which is important to the health and survival of humans. Adenophoreans help to cycle carbon and nitrogen and to breakdown organic matter in the soil environment.

Species accounts

List of Species

No common name

Desmoscolex squamosus

order

Desmoscolecida

family

Desmoscolecidae

taxonomy

Protricomoides squamosus Timm, 1970.

other common names

None known.

physical characteristics

Characterized by the annulation and ornamentation of the body cuticles, the shape of the head, the shape and arrangement of the somatic setae, and the copulatory apparatus. They have a small body that is tapered at both ends; the female body is longer than the male. The cuticle is annulated, with only the two anterior and the three posterior main rings being considered complete; that is, they are covered with a continuous narrow or wide layer of secretion and concretion material. The body cuticle has 70–71 annules (when counting complete main rings as single annules) in the holotype male and 73 annules in the paratype female. The annules contain a transverse row of minute pores with a small accumulation of secretion and concretion particles around them. at the level of the insertion of the somatic setae, the layer of concretion is larger.

The somatic setae are arranged in pairs, inserted on short peduncles or almost directly on the body cuticle, but they differ sub-dorsally and sub-ventrally. The sub-dorsal setae taper distally to a shorter spatulate tip, which is 0.0000787–0.000118 in (2–3 µm) in length. The sub-ventral setae are shorter than the sub-dorsal ones, and are all about equally long, except for the longer elongated terminal pair of sub-dorsal setae. The head is generally wider than long, with a wide truncated anterior end. The cuticle is thickened and sclerotized, except in the labial region and at the level of the amphids. From the insertion of the cephalis setae to about halfway along the head length, the cuticle is covered with concretion material. The labial zone has six papillae that are very small. the cephalic setae is jointed, with a length of 0.000118–0.000158 in (3–4 µm) at the base and a fine distal part.

Amphids are rounded and vesicular, mostly covering the head. The amphidial opening is large, and situated in the posterior region of the head. The digestive system is typical for its genus. the stoma is very small. The pharyngo-intestinal junction is opposite the posterior end of the second main ring. The intestine overlaps the rectum by a large blind sac, extending to halfway to the end ring of the paratype female. There are very small ochrous pigment spots situated at the level of annule 13. The cloacal tube protrudes from the ventral body wall in annule 64. Spicules are about 0.000945 in (24 µm) in length, and gradually taper to a tip. the gubernaculum is not observed. The tail has two main rings, with females also having two partial rings. The phasmata is not observed.

distribution

Not known; although the family Demoscolecida is found primarily in marine waters and occasionally in freshwater and soil. (Specific distribution map not available.)

habitat

Nothing is known.

behavior

Nothing is known.

feeding ecology and diet

Nothing is known.

reproductive biology

The reproductive system is typical for the genus. It is obscured because of the very enlarged intestine that contains many large globules. The female vulva is situated within annule 48. Males have one testis.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Greeffiella minutum

order

Desmoscolecida

family

Greeffiellidae

taxonomy

Greeffiella minutum Steiner, 1916.

other common names

None known.

physical characteristics

Adults are less than 0.00315 in (80 µm) in length, and considered by many scientists as the smallest of all the nematode species. The prominent annulation is homogeneous and, as a result, not mixed with smaller annules. Each annule bears a ring of elongated spines that do not pass through the cuticle. In addition, there are large subdorsal and subventral tubular setae along the body.

distribution

Live in the seas. (Specific distribution map not available.)

habitat

Found in marine habitat or, rarely, in brackish estuarine waters in sediment.

behavior

Free-living worms.

feeding ecology and diet

Nothing is known.

reproductive biology

Nothing is known.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Nygolaimus parvus

order

Dorylaimida

family

Nygolaimidae

taxonomy

Nygolaimus parvus Thorne, 1974.

other common names

None known.

physical characteristics

Classified as predatory and free-living, with a length of 0.051–0.055 in (1.3–1.4 mm). They are moderate-sized nematodes with relatively thin cuticles. The body is twisted so that when observed from an upper and lower viewpoint, only the head and tail can be seen. The neck takes up about two-thirds of the body length. The lip region is apparently set off by a modest constriction, with papillae low and rounded. The lateral field is one-fourth of the body width. The mural tooth is deltoid in shape, set in the left sub-ventral wall of the cheilostomal region, of length 0.000866 in (22 µm), a length that is somewhat less than the width of the lip region. The complete stoma is divided into three parts: a thin-walled cheilostomal vestibule, the cheilostome with the mural tooth, and an elongated thick-walled esophastome. The esophagus begins as a slender tube, and then slowly expands two-thirds of the way to the posterior, which then nearly fills the body cavity. A sheath encloses the posterior portion (postcorpus) of the esophagus. The three glands at the junction of the esophagus and stomach are well developed and discrete. At this site, the opening (cardia) is an elongated hemispheroid, which is one-fourth the body width and is usually obscured by the cardiac glands. The intestinal granules are colored a light brown, and sometimes form a slightly tessellated pattern. The rectum and pre-rectum both are about as long as the anal body diameter. Both sexes have similarly shaped tails, generally conoid and bluntly rounded.

distribution

Midwestern to western United States; especially in South Dakota, North Dakota, Minnesota, and Montana. (Specific distribution map not available.)

habitat

Live in native soils.

behavior

Classified as predatory and free-living.

feeding ecology and diet

Predacious on other small, soil-inhabiting organisms.

reproductive biology

The female vulva is transverse, and is smaller and of a different form than those of other species within the genus. The vagina extends about 40% of the body. The reflexed ovaries extend about two-thirds the distance back to the vulva. The eggs are 3–4 times as long as the body width. Males have lateral guiding pieces and poorly developed ventromedial supplements.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Mermis nigrescens

order

Stichosomida

family

Mermithidae

taxonomy

Mermis nigrescens Dujardin, 1842.

other common names

None known.

physical characteristics

A free-living adult and parasitic larvae species that infects the body cavity of grasshoppers. They are an unusually long and slender nematode, with a length of 1.97–7.87 in (5–20 cm), with females longer than males. Adult females are colored reddish brown at the anterior extremity, supposedly as an aid for light sensitivity. The terminal mouth has two closely associated lip papillae and four cephalic papillae placed further back. The crisscross fibers are distinct and the lateral chords are wide. The thick-walled brownish-colored eggs are small, divided in half by a distinct equatorial groove, and possessing prominent byssi (filamentous branches). The size of the eggs (larvae) is about 0.00276 in (70 µm) in length by 0.00118 in (30 µm) in width. When the grasshopper host ingests the eggs found on vegetation, which is usually grasses and plants, the juveniles will break open the egg at the equatorial groove and grow to a length of 3.9 in (10 cm) in a period lasting 1–3 months.

distribution

Commonly occur in the British Isles, Europe, and North America. (Specific distribution map not available.)

habitat

During their stage as developing larvae, they live primarily within locusts and grasshoppers, but may also infect other insect species. They may be located anywhere within the host's hemocoel (the body cavity where blood circulates). Once juveniles burrow out of a host, they will dig 6–8 in (15–20 cm) into the soil where they molt into adults. They are presumed to live in temperate forests and grasslands, rainforests, and mountains.

behavior

Adults are very agile and readily climb plants, especially during rainy seasons. During their adult stage while in the soil, there is no social interaction, except possibly to mate. Most nematodes will move away from light, but this is usually not the case for this species. Females may remain in the soil for several years before emerging pregnant into a lighted, moist environment in order to find a site on grasses and plants to lay eggs. They usually stay in the soil during the cold winter, sheltering under debris, and then emerging in late spring, during periods of overcast, humid weather. It is believed that they are able to discriminate between light levels with the use of melanin, which is a binary system (either off or on). Even though they sometimes will move toward light, they will die from continued exposure of direct sunlight.

The action of females crawling on plants in order to deposit their eggs on vegetation above ground is considered an important behavior modification for insect parasitism (most nematodes do not infect their hosts by depositing eggs on plant foliage that will be eaten). Extending from the sides of the eggs are long, filamentous brances, called byssi, which become entangled with the plant, thus holding them in place. After infecting a host, juveniles penetrate through the gut wall into the hemocoel. Once located within the hemocoel, the parasites consume the hemolymph. Many worms may infect the same host. By late summer, the abdomen of many grasshoppers will be packed with these parasites. Such infections seriously stress and sterilize infected grasshoppers. After this period of infestation, the grasshopper will usually die, upon which the species exits the body of its dead host. The remainder of life is largely spent in the soil, except when adult females emerge for egg deposition aboveground.

feeding ecology and diet

Developing juveniles consume large amounts of amino acids, lipids, and carbohydrates from the hemolymph of the host. The free-living adults do not eat, so they must gain all of their nutrients while in the insect host.

reproductive biology

During their post-parasitic stage, they live in the soil where they reach sexual maturity. Females may mate in the soil, but males are not necessarily needed for egg production. During or just after spring, females climb out of the soil onto vegetation where they deposit their eggs to await ingestion. Eggs can survive on foliage throughout the summer. They have an unusually large free-living stage when compared to other nematodes. A complete life cycle usually comprises of 2–3 years.

conservation status

Not listed by the IUCN. The parasitic species is common and widespread.

significance to humans

Since the larvae kill the host grasshopper upon emerging, they have the potential to be used as a biological control agent if their rate of survival within the soil should be extended and if their numbers could be supplemented when released into the soil. However, nematode ecology is poorly understood, especially in nature, and such control practices are still far off into the future.

Trichina worm

Trichinella spiralis

order

Stichosomida

family

Trichinellidae

taxonomy

Trichinella spiralis Owens, 1835.

other common names

English: Pork worm.

physical characteristics

Classified as animal (mammal) parasites and the causal organism of the disease trichinosis, they are small roundworms that live mainly in rats and other small mammals such as pigs that pick up the worm while rooting for food. Adults have a length of 0.055–0.158 in (1.4–4.0 mm), with males measuring 0.055–0.063 in (1.4–1.6 mm) in length and females 0.118–0.158 in (3.0–4.0 mm) in length. Males and females have distinct features. Females possess a uterus and vulva. The vulva is located near the middle of the esophagus, which is about one-third the length of the body. Males have a single gonad, but no copulatory spicule, and have an ejaculatory duct. Structures identifiable on both sexes include the muscular esophagus, stichosome, and intestine. Stichosomes are formed by a single short row of stichocytes, following a short muscular esophagus. The color of the external surface of the adult is translucent and white. Both sexes are more slender at the anterior than at the posterior, but do not have two distinct sections. The anus is nearly terminal and has a large papilla on each side of it.

distribution

They are found worldwide, especially in South America and Africa. (Specific distribution map not available.)

habitat

Found more commonly in temperate rather than tropical regions. Unlike many parasites that show a high degree of host specificity, they can be found in many species of carnivores and omnivores, and in virtually all mammals. They are found attached to or buried in the mucosa (mucous membrane) of the duodenum of their host.

behavior

Have no stages outside a host, which is unusual for helminth parasites. Their lifecycle begins when viable encysted larvae are eaten with the flesh of any meat-eating animal. When these infectious cysts are ingested, the juveniles are freed from the hard cysts by the dissolving action of stomach acids. The liberated juveniles pass to the duodenum where they go through four rapid molting periods within 27–29 hours and then mature within 1–2 days. Adults live in the gastrointestinal tract of their host. Mature males fertilize the females and then die. Mature females will penetrate the mucosa of the intestine and, within a few days, will begin laying pre-juveniles into lymph vessels. Females die after producing the juveniles. The new pre-juveniles are then carried to the lymphatic and mesenteric veins, and are found throughout the arterial circulation 7–25 days after the initial infection. The pre-juveniles move in the hepatoportal system through the liver, and then to the heart, lungs, and the arterial system, which distributes them throughout the body. They are transported to striated muscles, where they penetrate individual fibers. Within the muscles, the immature worms curl into a ball and encyst. Juvenile cysts can grow to 0.12 in (3 mm) in diameter. These newly infective juveniles are now ready to be eaten by another host (which eats the infected muscle of the previous host). If another host does not eat the previous host, then juveniles may remain viable for many years, for example, up to 25 years in humans and 11 years in pigs. Their lifecycle is considered to be complete when a definitive host ingests the intermediate host. There is general agreement among scientists that there are four juvenile stages of the worm, but there is distinct disagreement as to whether or not nematode development occurs within the cyst.

feeding ecology and diet

As parasites, they feed off of their hosts.

reproductive biology

The single female uterus is filled with developing eggs in its posterior portion, while the anterior region contains fully developed hatching juveniles. The size of the larvae is about 0.00394 in (100 µm) in length by 0.000394 in (10 µm) in width. After impregnating the female, the male dies. The females subsequently increase to their maximum size and burrow deeper into the mucosa. Females are ovoviviparous (very thinly shelled or shell-less eggs are developed within the female and juveniles hatch before leaving the uterus). A female produces about 1,500 young over a period of 4–6 weeks, after which the female dies. Both males and females live for only a short time in the intestinal epithelium of a wide variety of mammals. The juveniles then migrate into the intestinal lymphatic and mesenteric venules, on to the heart and lungs, and eventually into the arterial circulatory system. Concurrently, they molt three times in order to reach adulthood. When reaching striated muscle, they encyst, remaining viable for more than five years within the cysts. The termination of their lifecycle is reached at this time, and the larvae must wait for their host to be devoured in order to continue other stages.

conservation status

Not listed by the IUCN.

significance to humans

Trichinosis is a zoonotic infection associated with the colonization of worms in muscles. It is often found in humans because of the consumption of uncooked or insufficiently cooked pork products (though other animals are also potential sources). Trichinella is the third most common worm that infects humans. They cause nausea, dysentery, puffy eyes, and colic. They also cause pain and more severe problems such as edema, cardiac and pulmonary problems, deafness, delirium, muscle pain, muted reflexes, nervous disorders, and pneumonia. Their natural hosts are flesh-eating animals, especially humans, pigs, rats, and other mammals. Humans are considered accidental hosts because, under normal conditions, the parasite ends its cycle; that is, no other animals eat humans in order to transfer their larvae to other hosts. But concern for trichinosis is not as great today with improved pork production practices. Still, an estimated 5–6 million human infections are present at any one time in North America (about 2% of the population).

Human whipworm

Trichuris trichiura

order

Stichosomida

family

Trichuridae

taxonomy

Trichuris trichiusa Linnaes, 1771.

other common names

English: Whipworm, threadworm.

physical characteristics

Exceptionally thin for nematodes. They derive their name from the characteristic "whip-like" shape. Adults are 1.2–2.0 in (30–50 mm) in length, with a thread-like anterior end that becomes thicker at the posterior end. Both sexes have two distinct body regions. Males are 1.2–1.8 in (30–45 mm) in length, while adult females are 1.4–2.0 in (35–50 mm) in length. Females are very attenuated on the anterior three-fifths of the body, and become greatly expanded in the posterior two-fifths. Males are similarly shaped, but the swollen posterior is less pronounced. For most of the body's length, there is an area designated as the bacillary band, which is a combination of hypodermal and glandular tissues. The glandular tissue opens up to the exterior through cuticular pores. They have a mouth with a simple opening, and do not have lips. The buccal cavity is tiny and is provided with a minute spear. The esophagus is very long, occupying about two-thirds of the body length and consists of a thin-walled tube surrounded by large, unicellular glands, the stitchocytes. The entire structure is called a stichosome. The anterior end of the esophagus is somewhat muscular. The transition from the anterior, filiform portion of the esophagus and the posterior, stout portion is sudden. Both sexes have a single gonad, and the anus is near the tip of the tale. Males have a single spicule that is surrounded by a spiny spicule sheath. The ejaculatory duct joins the intestine anterior to the cloaca. In the female, the vulva is near the junction of the esophagus and the intestine. The uterus contains many unembryonated eggs. The excretory system is absent. The ventral surface of the esophageal region bears a wide band of minute pores, leading to underlying glandular and non-glandular cells.

distribution

Found worldwide, but are most commonly in Europe, followed by Asia, Africa, and South America. (Specific distribution map not available.)

habitat

Most often found in temperate and tropical areas, especially in moist areas. The final hosts are humans, where they primarily inhabit the colon.

behavior

After 10–14 days in soil, their eggs become infective. For the host to become infective, the eggs must be swallowed. Upon entering the host's body, larvae hatch in the small intestine where, over a short period of time, they grow and molt at various points along the intestines, including the lumen and ileocecal area. Adults eventually bury their thin, thread-like anterior half into the mucosa of the large intestine, and then feed on tissue secretions, but not blood. They complete maturation at this time with their large posterior end breaking out of the mucosa and protruding. Adults are characterized by a lack of a tissue migration phase. They can reach the lungs by way of the lymph and blood systems. In the lungs, the larvae break out of the pulmonary capillaries into the air sacs, ascend into the throat, and descend to the small intestine again, where they grow. From the time of ingestion of the eggs to the development of mature worms is approximately three months. The prepatent period in the final host is 4–12 weeks.

feeding ecology and diet

As parasites, they feed off of their human hosts, primarily receiving nutrients from tissue secretions mostly within the intestines; it does not feed on blood.

reproductive biology

The reproductive system is found at the esophago-intestine region. Both males and females have single reflexed gonads. The male has only one spicule. The eggs are operculate, and the females are oviparous. In early larval development, there are two rows of cells. When they infect a host, the eggs are "sticky." Eggs have, smooth outer shells. Adult females can lay eggs for up to five years. Egg production is estimated at 1,000–7,000 per day following copulation, and may contain up to 46,000 eggs at any one time. The eggs can be expelled with the feces of the host. Embryonation is completed in about 21 days in soil at about 86°F (30°C), where it is moist and shady. Adults can live for several years, so large numbers can accumulate in humans.

conservation status

Not listed by the IUCN.

significance to humans

Occasionally cause the condition eosinophilia, with the cecum and colon being the most commonly infected sites in the host. The particular disease is trichuriasis, or "whip worm" infection. In the United States, whipworm infection is rare overall, but is less rare in the rural southeast, where more than 2.2 million people are infected. Internationally, human whipworm infection is common in less-developed countries, with about 300–500 million people infected worldwide, but with some estimates as high as one billion people. Human whipworm infection is rarely fatal, but rectal prolapse may occur in heavily infected hosts. Fewer than 100 worms rarely cause clinical symptoms. Only hosts with very heavy infections become symptomatic. For those with heavy infection, common symptoms include abdominal discomfort, anemia, abdominal tenderness, secondary bacterial infections, and diarrhea; for more severe cases, symptoms include rectal prolapse, insomnia, nervousness, loss of appetite, vomiting, urticaria (skin rash), prolonged diarrhea, constipation, and flatulence. The infection is usually diagnosed by observing eggs in the patient's feces, and on occasion the presence of larval or adult worms in the feces.

Resources

Books

Farrand, John, ed. The Audubon Society Encyclopedia of Animal Life. New York: Clarkson N. Potter, 1982.

Bird, Alan F. The Structure of Nematodes. New York: Academic Press, 1971.

Chitwood, B. G., and M. B. Chitwood. Introduction to Nematology. Baltimore: University Park Press, 1950.

Croll, Neil A., and Bernard E. Matthews. Biology of Nematodes. Glasgow and London: Blackie and Son Limited, 1977.

Levin, Simon Asher, ed. Encyclopedia of Biodiversity. San Diego: Academic Press, 2001.

Maggenti, Armand. General Nematology. New York: Springer-Verlag, 1981.

Malakhov, V. V. (translated by George V. Bentz, edited by W. Duane Hope). Nematodes: Structure, Development, Classification, and Phylogeny. Washington, DC, and London, U.K.: Smithsonian Institution Press, 1994.

Mehlhorn, Heinz, ed. Encyclopedic Reference of Parasitology: Diseases, Treatment, Therapy, 2nd ed. New York: Springer, 2001.

The New Larousse Encyclopedia of Animal Life. New York: Bonanza Books, 1981.

Parker, Sybil P., ed. Synopsis and Classification of Living Organisms. New York: McGraw-Hill Book Company, 1982.

Poinar, George O. Jr. The Natural History of Nematodes. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1983.

Stone, A. R., H. M. Platt, and L. F. Khalil, eds. Concepts in Nematode Systematics, Special Volume No. 22. London: Academic Press, 1983.

Wharton, David A. A Functional Biology of Nematodes. London: Croom Helm, 1986.

William Arthur Atkins