Acanthocephala

(invertebrate zoology) The spiny-headed worms, a phylum of helminths; adults are parasitic in the alimentary canal of vertebrates.

(Thorny headed worms)

Phylum: Acanthocephala

Number of families: 22

Thumbnail description
Parasitic thorny headed worms with complex life cycles; sexes separated; adults found in intestines of vertebrates (definitive host), larvae found in hemocoel (body cavity) of arthropods (intermediate hosts) and sometimes in body cavities of vertebrates (paratenic or transport hosts)

Evolution and systematics

As with most soft-bodied parasites, no fossil record of acanthocephalans is known. However, prehistoric human coprolites at archeological sites in the United States and Brazil have revealed infections by acanthocephalans. Additionally, some 9,000-year-old animal coprolites also from Brazil have been found to contain acanthocephalan eggs. The phylum Acanthocephala is divided into 3 major taxonomic groups: the Archiacanthocephala, Eoacanthocephala, and Palaeacanthocephala, which are considered by some to be classes and others to be orders. A fourth group, the Polyacanthocephala, has been proposed but its status is controversial. Taxonomic groups are based on morphological characters of the worms as well as their hosts' taxonomy and ecology, and such division is supported by molecular data. Molecular, morphological, and ultrastructural analysis of 18S ribosomal DNA sequences has revealed that acanthocephalans and their closest living relatives, members of the phylum Retifera, should be in one clade—referred to as the Syndermata. Acanthocephalans include 22 families and about 1,000 species.

Physical characteristics

Adults are cylindrical or slightly flattened worms that are usually white or colorless; however, some species may be yellow, brown, red, or orange. Acanthocephalans are never segmented, although some species exhibit superficial pseudosegmentation. As adults acanthocephalans measure from less than an inch (a few millimeters) to more than 24 in (60 cm) in length, with the archiacanthocephalans being the largest ones. These worms are sexually dimorphic with females usually larger than males. Structurally, the worms may be divided into three body regions: a proboscis, a neck, and a trunk. The proboscis harbors hooks that may be arranged either in rows or longitudinal lines depending upon the species. Some species harbor an apical organ at the tip of the proboscis that is presumably sensory. The proboscis invaginates into a proboscis receptacle hanging into the anterior part of the trunk. The neck is unarmed but may show lateral organs that may be involved in sensory perception. The trunk may or may not be armed with spines whose distribution is an important criterion for species identification. Acanthocephalans are pseudocoelomate with a syncitial tegument within which runs a lacunar system (an interconnected fluid-filled network of cavities). These worms also have hollow tubular muscles and lemnisci (sac-like structures hanging from the base of the neck into the pseudocoel) that are connected to the proboscis lacunar system. Unique features of acanthocephalan genitalia are a uterine bell in females and cement glands, the organ of Saefftigen, and the copulatory bursa in males. Both males and females have a cerebral ganglion in the proboscis receptacle, and males have genital ganglia and a bursal ganglion. All internal organs are derived from a ligament running down the center of the pseudocoel.

Distribution

Acanthocephalans are found throughout the world, including in fish at deep-sea hydrothermal vents.

Habitat

Adults are intestinal parasites of mammals, birds, fishes, amphibians, and reptiles. Larvae develop in the hemocoel of mandibulate arthropods (crustaceans, myriapods, and insects).

Behavior

Acanthocephalans usually occupy precise niches within the intestines of their definitive hosts. However, some species have been shown to migrate along the intestinal tract during the term of infection. Such migration is correlated with both host diet and sexual maturity of the worms. Nothing is known of acanthocephalan behavior and communication, and there is no evidence of chemical attractants being released to assist in mates finding each other within the hosts' digestive tract. However, acanthocephalans are known to modify the behavior of both their definitive host (e.g., to induce giddiness) and intermediate hosts (e.g., to induce positive phototropism or decrease/alter intermediate host evasive responsiveness). Further, some species also selectively alter the coloration of their intermediate hosts. Such alterations are known to favor transmission of acanthocephalan infective stages to their definitive hosts via increasing intermediate host susceptibility to predation. Disruption of definitive host behavior is speculated to affect transmission by altering host distribution and selection of habitat. Because acanthocephalans attach themselves to the intestinal wall of their host, they may induce pathology, such as inflammation of the surrounding tissues, perforation of the intestinal wall, peritonitis, enlargement of the intestine, and edema, in their host. Results of infection may be fatal while other cases may appear to be mild; oftentimes, more numerous the worms, the more serious the infection. Further, some acanthocephalans have been shown to disrupt host digestion and energy metabolism, which has been shown to have serious detrimental effects during periods of host stress.

Feeding ecology and diet

Acanthocephalans have no digestive tract but selectively absorb nutrients from the host's intestine across their tegument. However, knowledge in this area is limited and is based on only a few species whose feeding and metabolism have been studied (see below Moniliformis moniliformis). The major substrate for acanthocephalan metabolism is carbohydrate, with ethanol being the main end product. Uptake of monosaccharides appears to involve active transport mechanisms. Some species may store glucose in the proboscis receptacle muscle, and intense labeling of the cytoplasmic core of the hollow muscles following uptake of radiolabled glucose occurs. However, it has not been reported whether this latter area acts as a storage site, or whether it plays a role in distributing nutrients throughout the body. The plasma membrane at the surface of the tegument shows hydrolytic activity and tegumental surface crypts within which various enzymatic activities have been localized. These crypts increase the absorptive surface area and are considered to be extra-cytoplasmic digestive organelles. Various amino acids are known to be absorbed through the tegumental surface, but their role in metabolism is not clear. Routes of absorption also vary according to the amino acid studied. Lipids are absorbed and then stored in the lemnisci, although controversy exists as to whether the primary site of lipid absorption is the body wall or the neck/proboscis region. While large amounts of lipids may be deposited in acanthocephalans, they are not thought to be used in metabolism.

Reproductive biology

Female and male acanthocephalans copulate in the intestine of their vertebrate definitive hosts. Fertilization is internal and it is thought that males initiate copulation. The male bursa, the spines that both males and females may harbor at the very posterior end of their trunks, as well as the "cement" (mucilaginous and proteinaceous material) discharged from the male's cement gland(s), all appear to play a role in strengthening the copulatory union. Cement plugs/caps are often observed at the posterior extremities of females, although the role of these plugs is still under discussion. The favored hypothesis is that the cap, which lasts a few days, prevents the loss of injected sperm and further prevents sperm from competing males to enter the female. Cement plugs are also often observed on males, which may serve to prevent male competitors from copulating.

Not all acanthocephalans show seasonality in their life cycle, but there are many instances in which they do. When seasonal life cycles exist there is often a direct link to change in host diet, water temperature, and/or the presence of intermediate hosts in the environment. Maturation of acanthocephalans is sometimes correlated to the maturation of their definitive hosts. Females have ovaries that break up into ovarian balls, which in turn produce oocytes. Once fertilized oocytes become eggs, they float freely in the pseudocoel while the larvae within them develops into an acanthor. During larval maturation eggs are sorted via the uterine bell, which returns immature eggs to the pseudocoel while directing mature eggs containing acanthors to the uterus where they are stored until release. Mature eggs are released via a gonopore into the lumen of the host's intestine and are excreted with the feces. Once outside the host, the eggs must be consumed by the intermediate host to assure transmission. The eggs of acanthocephalans are the only free-living stages of the parasites. Eggs have four envelopes (exceptions exist) that are separated by interstices. Although all analyzed acanthocephalan eggs contain keratin in their second shell, other chemical structures exist and differences among palae-, archi-, and eoacanthocephalan shell structure probably reflect differences in the nature of the intermediate hosts among the three groups. Eggs contain the acanthor, which is the infective stage of the parasite for the intermediate hosts. Acanthors harbor at their anterior end a boring structure called the aclid organ, which consists of a pair of "blades." Acanthors of most species are covered with spines that decrease in size posteriorly. Acanthors of some species also exhibit hooks on their anterior part. Once the intermediate host ingests the egg, the acanthor hatches and uses the aclid organ to penetrate the intestinal wall and then develops, often first beneath the intestinal serosa and then in the hemocoel. Development generally lasts several weeks as the acanthor first transforms into the acanthella and then into a cystacanth, which is the infective stage for the definitive host.

With the exception of size and sexual maturity, cystacanths show all the morphological features of an adult. A thin membrane whose origin is still under discussion surrounds the cystacanths of most species and may serve to protect against the invertebrate host's immuno-defense system. Once intermediate hosts carrying cystacanths are ingested by the correct definitive host, the life cycle is completed. Some cycles include paratenic (transport) hosts, which are vertebrates that ingest infected intermediate hosts and within which the larvae do not develop further. Paratenic hosts oftentimes accumulate large numbers of infective cystacanths and may be required to assure that the parasites reach a definitive host that is higher in the food web. In paratenic hosts the cystacanths most often penetrate the intestinal wall and stay in the body cavity. Within these hosts, accumulated cystacanths are usually attached to the intestinal mesenteries, awaiting paratenic host ingestion by an appropriate definitive host. Postcyclic parasitism may also occur when predators of a definitive host ingest adult acanthocephalans and in turn become parasitized themselves. As such, acanthocephalans may be transferred via cannibalism within a definitive host population.

Conservation status

Little is known about the status of most acanthocephalans. Declines, occurrences, or commonality would all be linked directly to the status of the life cycle, i.e., to the presence of all hosts, and can thus be adversely affected by habitat loss/disruption.

Significance to humans

Very few species of acanthocephalans are known to induce acanthocephaliasis in humans. Symptoms such as giddiness, acute abdominal pain, tinnitus, edema, constipation, diarrhea, undernutrition, and underdevelopment have been reported. The disease is fairly rare (only several hundred cases reported) but may be fatal. Humans obtain the parasite by ingesting infected intermediate hosts either accidentally, as part of their regular diet, or for medicinal purposes. In the former case children are most often affected. Eating sashimi (or raw fish in general) may also be a way for humans to become infected with acanthocephalans. Acanthocephalans, particularly those parasitizing fish, are known to selectively accumulate toxic heavy metals, such as lead and cadmium, in extremely high proportion relative to their surrounding host tissues and host environment. Consequently, their potential use in monitoring polluted environments is an active avenue of research.

Species accounts

Resources

Crompton, D. W. T., and Brent B. Nickol. Biology of the Acanthocephala. Cambridge: Cambridge University Press, 1985.

Moore, Janice. Parasites and the Behavior of Animals. New York and Oxford: Oxford University Press, 2002

Muller, Ralph. Worms and Human Diseases. Cambridge, MA: CABI Publishing, 2002.

Neafie, Ronald C., and Aileen M. Marty. "Acanthocephaliasis." In Pathology of Infectious Diseases, vol.1, Helminthiases, edited by W. M. Meyers. Armed Forces Institute of Pathology, American Registry of Pathology, 2000.

Taraschewski, Horst. "Host-Parasite Interactions in Acanthocephala: A Morphological Approach." In Advances in Parasitology, vol. 46, edited by J. R. Baker, R. Muller, and D. Rollinson. San Diego: Academic Press, 2000.

Garcia-Varela, M., M. P. Cummings, G. Perez-Ponce de Leon, S. L. Gardner, and J. P. Laclette. "Phylogenetic Analysis Based on 18S Ribosomal RNA Gene Sequences Supports the Existence of Class Polyacanthocephala (Acanthocephala)." Molecular Phylogenetics and Evolution 23 (2002): 288–292.

Garcia-Varela, M., G. Perez-Ponce de Leon, P. de la Torre, M. P. Cummings, S. S. S. Sarma, and J. P. Laclette. "Phylogenetic Relationships of Acanthocephala Based on Analysis of 18S Ribosomal RNA Gene Sequences." Journal of Molecular Evolution 50: 532–540.

Golvan, Y. J. "Nomenclature of the Acanthocephala." Research and Reviews in Parasitology 54, no.3 (1994): 135–205.

Goncalves, M. L. C., A. Araujo, and L. F. Ferreira. "Human Intestinal Parasites in the Past: New Findings and a Review." Memorias do Instituto Oswaldo Cruz 98, suppl.1 (2003): 103–118.

Herlyn, H., O. Piskurek, J. Schmitz, U. Ehlers, and H. Zischler. "The Sundermatan Phylogeny and the Evolution of Acanthocephalan Endoparasitism as Inferred from 18S rDNA Sequences." Molecular Phylogenetics and Evolution 26 (2003): 155–164.

[Article by: Isaure de Buron, PhD; Vincent A. Connors, PhD]

A distinct phylum of helminths, the adults of which are parasitic in the alimentary canal of vertebrates. They are commonly known as the spiny-headed worms. The phylum comprises the orders Archiacanthoceph-ala, Palaeacanthocephala, and Eocanthocephala. Over 500 species have been described from all classes of vertebrates, although more species occur in fish than in birds and mammals and only a relatively few species are found in amphibians and reptiles. The geographical distribution of acanthocephalans is worldwide, but genera and species do not have a uniform distribution because some species are confined to limited geographic areas. Host specificity is well established in some species, whereas others exhibit a wide range of host tolerance. The same species never occurs normally, as an adult, in coldblooded and warm-blooded definitive hosts. More species occur in fish than any other vertebrate; however, Acanthocephala have not been reported from elasmobranch fish. The fact that larval development occurs in arthropods gives support to the postulation that the ancestors of Acanthocephala were parasites of primitive arthropods during or before the Cambrian Period and became parasites of vertebrates as this group arose and utilized arthropods for food. See also Palaeacanthocephala.

Adults of various species show great diversity in size, ranging in length from 0.04 in. (1 mm) in some species found in fish to over 16 in. (400 mm) in some mammalian species.

The body of both males and females has three subdivisions: the proboscis armed with hooks, spines, or both; an unspined neck; and the posterior trunk. The proboscis is the primary organ for attachment to the intestinal wall of the host. In most species the proboscis is capable of introversion into a saclike structure, the proboscis receptacle. The proboscis receptacle and neck can be retracted into the body cavity but without inversion. The body cavity, or pseudocode, contains all the internal organs, the most conspicuous of which are the reproductive organs. There is no vestige of a digestive system in any stage of the life cycle. The reproductive organs of the male consist of a pair of testes and specialized cells, the cement glands. The products of the testes and cement glands are discharged through a penis. Female Acanthocephala are unique in that the ovary exists as a distinct organ only in the very early stages of development and later breaks up to form free-floating egg balls. The eggs are fertilized as they are released from the egg balls and are retained within the ligament sacs until embry-onation is complete. The nervous system is composed of a chief ganglion or brain located within the proboscis receptacle. Two nerve trunks pass through the wall of the proboscis receptacle to innervate the trunk wall. Modified protonephridial organs are found closely adherent to the reproductive system, but in most species specialized excretory organs are completely lacking.

A phylum of elongate, mostly cylindrical organisms (thorny-headed worms) parasitic in the intestines of all classes of vertebrates.

For other uses, see Acanthocephala (disambiguation).

Acanthocephala
Corynosoma Wegeneri
Scientific classification
Kingdom:	Animalia
Subkingdom:	Eumetazoa
(unranked):	Bilateria
Superphylum:	Platyzoa
Phylum:	Acanthocephala Kohlreuther, 1771
Classes
Archiacanthocephala Eoacanthocephala Palaeacanthocephala

The Acanthocephala (Greek ακανθος, akanthos, thorn + κεφαλη, kephale, head) is a phylum of parasitic worms known as acanthocephales, thorny-headed worms, or spiny-headed worms, characterised by the presence of an evertable proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host. Acanthocephalans typically have complex life cycles, involving a number of hosts, including invertebrates, fishes, amphibians, birds, and mammals. About 1150 species have been described.

The Acanthocephala were thought to be a discrete phylum. Recent genome analysis has shown that they are descended from, and should be considered as, highly modified rotifers.^[1] This is an example of molecular phylogenetics.

Contents 1 Morphological characteristics 1.1 Digestion 1.2 Proboscis 1.3 Phylogenetic relationships 1.4 Size 1.5 Skin 1.6 Nervous system 1.7 "Brain-jacking" 1.8 Sex 1.9 Other features 2 History 3 Life cycles 3.1 General patterns 3.2 An example - Polymorphus spp. 4 See also 5 References 6 External links

Morphological characteristics

There are several morphological characteristics that distinguish acanthocephalans from other phyla of parasitic worms.

Digestion

Acanthocephalans lack a mouth or alimentary canal. This is a feature they share with the cestoda (tapeworms), although the two groups are not closely related. Adult stages live in the intestines of their host and uptake nutrients which have been digested by the host, directly, through their body surface.

Proboscis

The most notable feature of the acanthocephala is the presence of an anterior, protrudible proboscis that is usually covered with spiny hooks (hence the common name: thorny headed worm). The proboscis bears rings of recurved hooks arranged in horizontal rows, and it is by means of these hooks that the animal attaches itself to the tissues of its host. The hooks may be of two or three shapes, usually, longer, more slender hooks are arranged along the length of the proboscis, with several rows of more sturdy, shorter nasal hooks around the base of the proboscis. The proboscis is used to pierce the gut wall of the final host, and hold the parasite fast while it completes its life cycle. Like the body, the proboscis is hollow, and its cavity is separated from the body cavity by a septum or proboscis sheath. Traversing the cavity of the proboscis are muscle-strands inserted into the tip of the proboscis at one end and into the septum at the other. Their contraction causes the proboscis to be invaginated into its cavity. The whole proboscis apparatus can also be, at least partially, withdrawn into the body cavity, and this is effected by two retractor muscles which run from the posterior aspect of the septum to the body wall. Some of the acanthocephalans(perforating acanthocephalans) can insert their proboscis in the intestine of the host and open the way to the abdominal cavity. [1]

Some key features of acanthocephalan morphology

Phylogenetic relationships

Acanthocephalans are highly adapted to a parasitic mode of life, and have lost many organs and structures through evolutionary processes. This makes determining relationships with other higher taxa through morphological comparison problematic. Phylogenetic analysis of the 18S ribosomal gene has revealed that the Acanthocephala are most closely related to the rotifers, or may even belong in that phylum. The two are included among the Platyzoa.

Size

The size of the animals varies greatly, from forms a few millimetres in length to Gigantorhynchus gigas, which measures from 100 to 650 mm.

Skin

The body surface of the acanthocephala is peculiar. Externally, the skin has a thin cuticle covering the epidermis, which consists of a syncytium with no cell walls. The syncytium is traversed by a series of branching tubules containing fluid and is controlled by a few wandering, amoeboid nuclei. Inside the syncytium is an irregular layer of circular muscle fibres, and within this again some rather scattered longitudinal fibres; there is no endothelium. In their micro-structure the muscular fibres resemble those of nematodes.

Except for the absence of the longitudinal fibres the skin of the proboscis resembles that of the body, but the fluid-containing tubules of the proboscis are shut off from those of the body. The canals of the proboscis open into a circular vessel which runs round its base. From the circular canal two sac-like projections called the lemnisci run into the cavity of the body, alongside the proboscis cavity. Each consists of a prolongation of the syncytial material of the proboscis skin, penetrated by canals and sheathed with a muscular coat. They seem to act as reservoirs into which the fluid which is used to keep the proboscis "erect" can withdraw when it is retracted, and from which the fluid can be driven out when it is wished to expand the proboscis.

Nervous system

The central ganglion of the nervous system lies behind the proboscis sheath or septum. It innervates the proboscis and projects two stout trunks posteriorly which supply the body. Each of these trunks is surrounded by muscles, and this nerve-muscle complex is called a retinaculum. In the male at least there is also a genital ganglion. Some scattered papillae may possibly be sense-organs.

"Brain-jacking"

Thorny-headed worms begin their life cycle inside invertebrates that reside in marine or freshwater systems. Gammarus lacustris, a small crustacean that feeds near ponds and rivers, is one invertebrate that the thorny-headed worm may occupy. This crustacean is predated by ducks and hides by avoiding light and staying away from the surface. However, when infected by a thorny-headed worm it becomes attracted toward light and surfaces itself. Gammarus lacustris will even go so far as to find a rock or a plant on the surface, clamp its mouth down, and latch on, making it easy prey for the duck. The duck is the definitive host for the acanthocephalan parasite. In order to be transmitted to the duck, the parasite's intermediate host (the gammarid) must be eaten by the duck. This modification of gammarid behavior by the acanthocephalan is thought to increase the rate of transmission of the parasite to its next host by increasing the susceptibility of the gammarid to predation.

It is thought that when Gammarus lacustris is infected with a thorny-headed worm, the parasite causes serotonin to be massively expressed. Serotonin is a neurotransmitter involved in emotions and mood. Researchers have found that during mating Gammarus lacustris expresses high levels of serotonin. Also during mating, the male Gammarus lacustris clamps down on the female and holds on for days. Researchers have additionally found that blocking serotonin releases clamping. Another experiment found that serotonin also reduces the photophobic behavior in Gammarus lacustris. Thus, it is thought that the thorny-headed worm physiologically changes the behavior of the Gammarus lacustris in order to enter its final host, the bird.

Sex

The Acanthocephala are dioecious. There is a structure called the genital ligament which runs from the posterior end of the proboscis sheath to the posterior end of the body. In the male, two testes lie on either side of this. Each opens in a vas deferens which bears three diverticula or vesiculae seminales. The male also possesses three pairs of cement glands, found behind the testes, which pour their secretions through a duct into the vasa deferentia. These unite and end in a penis which opens posteriorly.

In the female, the ovaries are found, like the testes, as rounded bodies along the ligament. From these masses of ova dehisce into the body cavity and float in its fluid. Here the eggs are fertilized and segment so that the young embryos are formed within their mother's body. The embryos escape into the uterus through the uterine bell, a funnel like opening continuous with the uterus. At the junction of the bell and the uterus there is a second small opening situated dorsally. The bell "swallows" the matured embryos and passes them on into the uterus, and from there, out of the body via the oviduct. Should the bell swallow any of the ova, or even one of the younger embryos, these are passed back into the body cavity through the second, dorsal, opening.

The embryo passes from the body of the female into the alimentary canal of the host and leaves this with the feces.

Other features

A curious feature shared by both larva and adult is the large size of many of the cells, e.g. the nerve cells and cells forming the uterine bell. Polyploidy is common, with up to 343n having been recorded in some species. The acanthocephalans lack an excretory system, although some species have been shown to possess flame cells (protonephridia).

History

The earliest recognisable description of Acanthocephala - a worm with a proboscis armed with hooks - was made by Italian author Francesco Redi (1684). In 1771 Koelreuther proposed the name Acanthocephala. Muller independetly called them Echinorhynchus in 1776. Rudolphi in 1809 formally named them Acanthocephala.

Currently the phylum is divided into four classes - Palaeacanthocephala, Archiacanthocephala, Polyacanthocephala and Eoacanthocephala.

Life cycles

Adult Pomphorhynchus in a bluefish

General patterns

Acanthocephalans have complex life cycles, involving a number of hosts, for both developmental and resting stages. Complete life cycles have been worked out for only 25 species. Having been expelled by the female, the acanthocephalan embryo is released along with the feces of the host. For development to occur, the embryo needs to be ingested by an invertebrate, almost always a crustacean (there is one known life cycle which uses a mollusc as a first intermediate host). Inside the intermediate host, the acanthocephalan penetrates the gut wall, moves into the body cavity, encysts, and begins transformation into the infective cystacanth stage. This form has all the organs of the adult save the reproductive ones. The parasite is released when the first intermediate host is ingested. This can be by a suitable final host, in which case the cystacanth develops into a mature adult, or by a paratenic host, in which the parasite again forms a cyst. When consumed by a suitable final host, the cycstacant excysts, everts its proboscis and pierces the gut wall. It then feeds, grows and develops its sexual organs. Adult worms then mate. The male uses the excretions of its cement glands to plug the vagina of the female, preventing subsequent matings from occurring. Embryos develop inside the female, and the life cycle repeats.

An example - Polymorphus spp.

A diagram of the life cycle of Polymorphus spp.

Polymorphus spp. are parasites of seabirds, particularly the Eider Duck (Somateria mollissima). Heavy infections of up to 750 parasites per bird are common, causing ulceration to the gut, disease and seasonal mortality. Recent research has suggested that there is no evidence of pathogenicity of Polymorphus spp. to intermediate crab hosts. The cystacanth stage is long lived and probably remains infective throughout the life of the crab.

The life cycle of Polymorphus spp. normally occurs between sea ducks (e.g. eiders and scoters) and small crabs. Infections found in commercial-sized lobsters in Canada were probably acquired from crabs that form an important dietary item of lobsters. Cystacanths occurring in lobsters can cause economic loss to fishermen. There are no known methods of prevention or control.

See also

Wikispecies has information related to: Acanthocephala

• Cestoda
• Digenea
• Monogenea

References

This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate. (April 2009)

Wikisource has the text of the 1911 Encyclopædia Britannica article Acanthocephala.

1. ^ Shimek, Ronald Ph.D (January 2006). "Nano-Animals, Part I: Rotifaers". Reefkeeping.com. http://reefkeeping.com/issues/2006-01/rs/index.php. Retrieved 2008-07-27. 

• Lühe, M. (1904). 'Geschichte und Ergebnisse der Echinorhynchen-Forschung bis auf Westrumb (1821)', Zoologische Ann.... Zeitschift, 1, 139-250.
• Amin, O. M. (1987). Key to the families and subfamilies of Acanthocephala, with erection of a new class (Polyacanthocephala) and a new order (Polyacanthorhynchida). Journal of Parasitology, 73, 1216-1219.
• Zimmer, C. Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures 92. IBSN-13: 978-0-7432-0011-0 ISBN 0-7432-0011-X.
• Helluy & Thomas 2002 Proc. Royal.
• Tain, L, et al. "Altered Host Behavior and Brain Serotonergic Activity Caused by Acanthocephalans; Evidence for Specificity." The Royal Society, 2006.

• List of published articles about different species in international journals [2]

External links

Wikimedia Commons has media related to: Acanthocephala

Wikisource has the text of a 1911 Encyclopædia Britannica article about Acanthocephala.

• Fishdisease.net
• Review
• Review
• Images
• Parasites World

v • d • e Opisthokonta: Extant phyla of kingdom Animalia by subkingdom Parazoa Porifera (Calcarea, Demospongiae, Hexactinellida) · Placozoa (Trichoplax) Mesozoa Orthonectida · Rhombozoa Eumetazoa Radiata Ctenophora · Cnidaria (Anthozoa, Hydrozoa, Scyphozoa, Cubozoa, Staurozoa, Myxozoa) Bilateria Protostomia Ecdysozoa Cycloneuralia: Scalidophora (Kinorhyncha, Loricifera, Priapulida) · Nematoida (Nematoda, Nematomorpha) Panarthropoda: Onychophora · Tardigrada · Arthropoda Spiralia Platyzoa Platyhelminthes · Gastrotricha Gnathifera: Rotifera · Acanthocephala · Gnathostomulida · Micrognathozoa · Cycliophora Lophotrochozoa Trochozoa (Sipuncula, Nemertea, Mollusca, Annelida, Echiura) Lophophorata (Bryozoa, Entoprocta, Phoronida, Brachiopoda) Deuterostomia Ambulacraria Hemichordata · Echinodermata · Xenoturbellida Chordata Craniata (Vertebrata, Hyperotreti) · Cephalochordata · Tunicata Basal/disputed Acoelomorpha (Acoela, Nemertodermatida) · Chaetognatha

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)