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

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

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

References

  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


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

ACANTHOCEPHALA, a compact group of cylindrical, parasitic worms, with no near allies in the animal kingdom. Its members are quite devoid of any mouth or alimentary canal, but have a well-developed body cavity into which the eggs are dehisced and which communicates with the exterior by From Cambridge Natural History, vol. ii., "Worms, &c.," by permission of Macmillan& Co., Ltd.

FIG. I.

A, Five specimens of Echinorhynchus acus, Rud., attached to a piece of intestinal wall, X 4.

B, The proboscis of one still more highly magnified.

means of an oviduct. The size of the animals varies greatly, from forms a few millimetres in length to Gigantorhynchus gigas, which measures from 10 to 65 cms. The adults live in great numbers in the alimentary canal of some vertebrate, usually fish, the larvae are as a rule encysted in the body cavity of some invertebrate, most often an insect or crustacean, more rarely a small fish. The body is divisible into a proboscis and a trunk with sometimes an intervening neck region. 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. 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 (fig. 2). But 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 (fig. 3).

The skin is peculiar. Externally is a thin cuticle; this covers the epidermis, which consists of a syncytium with no cell limits. The syncytium is traversed by a series of branching tubules containing fluid and is controlled by a few wandering, amoeboid nuclei (fig. 2). Inside the syncytium is a not very regular layer of circular muscle fibres, and within this again some rather scattered longitudinal fibres; there is no endothelium. In their minute 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 latter are shut off from those of the body. The canals of the proboscis open ultimately into a circular vessel which runs round its base. From the circular canal two sac-like diverticula called the From Cambridge Natural History, vol. ii., "Worms, &c.," by permission of Macmillan & Co., Ltd.

FIG. 2. - A longitudinal section through the anterior end of Echinorhynchus haeruca, Rud. (from Hamann).

a, The proboscis not fully ex- h, One of the spaces in the sub b, Proboscis-sheath. [panded. cuticular tissue.

c, Retractor muscles of the pro- i, Longitudinal muscular layer.

d, Cerebral ganglion. [boscis. j, Circular muscular layer.

e, Retinaculum enclosing a k, Line of division between the nerve. sub-cuticular tissue of the f, One of the retractors of the trunk and that of the pro g, A lemniscus. [sheath. boscis with the lemnisci.

"lemnisci" depend into the cavity of the body (fig. 2). Each consists of a prolongation of the syncytial material of the proboscis skin, penetrated by canals and sheathed with a scanty muscular coat. They seem to act as reservoirs into which the fluid of the tense, extended proboscis can withdraw when it is retracted, and from which the fluid can be driven out when it is wished to expand the proboscis.

There are no alimentary canal or specialized organs for circulation or for respiration. Food is imbibed through the skin from the digestive juices of the host in which the Acanthocephala live.

J. Kaiser has described as kidneys two organs something like minute shrubs situated dorsally to the generative ducts into which they open. At the end of each twig is a membrane pierced by pores, and a number of cilia depend into the lumen of the tube; these cilia maintain a constant motion.

The central ganglion of the nervous system lies in the proboscissheath or -septum. It supplies the proboscis with nerves and gives off behind two stout trunks which supply the body (fig. 2). Each of these trunks is surrounded by muscles, and the complex retains the old name of "retinaculum." In the male at ea least there is also a genital ganglion. Some scattered papillae may possibly be sense-organs.

The Acanthocephala are dioecious. There is a "stay" called the "ligament" which runs from the hinder end of the proboscissheath to the posterior end of the body. In this the two testes lie (fig. 3). Each opens in a vas deferens which bears three diverticula or vesiculae seminales, and three pairs of cement glands also are found which pour their secretions through a duct into the vasa deferentia. The latter unite and end in a penis which opens posteriorly.

The ovaries arise like the testes as rounded bodies in the ligament. From these masses of ova dehisce into the body cavity and float in its fluid. Here the eggs are fertilized and here they segment so that the young embryos are formed within their mother's 9 body. The embryos escape into the uterus through the "bell," a funnellike opening continuous with the uterus. Just at the junction of the "bell" and the uterus there is a second small opening situated dorsally.

m The "bell" swallows the matured embryos and passes them on into the uterus, and thus out of the body via the oviduct, which opens at one end into the uterus and at the other on to the exterior at the posterior end of o.-- the body. But 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 and dorsal opening.

The embryo thus passes from the body of the female into the alimentary canal of the host and leaves this with the faeces. It is then, if lucky, eaten by some crustacean, or insect, more rarely by a fish. In the stomach it casts its membranes and becomes mobile, bores through the stomach walls and encysts usually in the bodycavity of its first and invertebrate host. By this time the embryo has all the organs of the adult perfected save only the reproductive; these develop only when the first host is swallowed by the second or final host, in which case the parasite attaches itself to the wall of the alimentary canal and becomes adult.

A curious feature shared by both larva and adult is the large size of many of the cells, e.g. the nerve cells and the bell.

O. Hamann has divided the group into three families, to which a fourth must be added.

(i.) Fam. Echinorhynchidae. This is by far the largest family and contains the commonest species; the larva of Echinorhynchus proteus lives in Gammarus pulex and in small fish, the adult is common in many fresh-water fish: E. polymorphus, larval host the crayfish, adult host the duck: E. angustatus occurs as a larva in Asellus aquaticus, as an adult in the perch, pike and barbel: E. moniliformis has for its larval host the larvae of the beetle Blaps mucronata, for its final host certain mice, if introduced into man it lives well: E. aces is common in whiting: E. porrigeus in the fin-whale, and E. strumosus in the seal. A species named E. hominis has been described from a boy.

Fam. Gigantorhynchidae. A small family of large forms with a ringed and flattened body. Gigantorhynchus gigas lives normally in the pig, but is not uncommon in man in South Russia, its larval host is the grub of Melolontha vulgaris, Cetonis auratus, and in America probably of Lachnosterna arcuata: G. echinodiscus lives in the intestine of ant-eaters: G. spira in that of the From Cambridge Natural History, vol. ii., "Worms &c.," by permission of Macmillan & Co., Ltd.

FIG. 4.

A, The larva of Echinorhynchus proteus from the body cavity of Phoxinus laevis, with the proboscis retracted and the whole still enclosed in a capsule.

B, A section through the same; a, the invaginated proboscis; b, proboscis sheath; c, beginning of the neck; d, lemniscus. Highly magnified (both from Hamann).

king vulture, Sarcorhampus papa, and G. taeniodes in Dicholopus cristatus, a cariama.

(iii.) Fam. Neorhynchidae. Sexually mature whilst still in the larval stage. Neorhynchus clavaeceps in Cyprinus carpio has its larval form in the larva of Sialis lutaria and in the leech Nephelis octocula: N. agilis is found in Mugil auratus and M. cephalus. (iv.) A pororhynchidae. With no proboscis. This family contains the single species Apororhynchus hemignathi, found near the anus of Hemignathus procerus, a Sandwich Island bird.

Authorities. - O. Hamann, O. Jen. Zeitschr. xxv., 1891, p. 113; Zool. Anz. xv., 1892, 195; J. Kaiser, Bibl. Zool. ii., 1893; A. E. Shipley, Quart. Journ. Micr. Sci. xxxix., 1896; ibid. xlii., 1899, p. 361; Villot, Zool. Anz. viii., 1885, p. 19.

(A. E. S.) e-


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Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

Contents

Translingual

Etymology

From Ancient Greek ἄκανθος (akanthos), acanthus) + κεφαλή (kephalē), head)

Proper noun

Acanthocephala

  1. (taxonomy) A taxonomic phylum within the superphylum Protostomiaintestinal worms, having the proboscis armed with recurved spines.
  2. (taxonomy) A taxonomic genus within the family Coreidae — leaf-footed bugs.

Hyponyms

  • (phylum):
  • Archiacanthocephala
  • Eoacanthocephala
  • Palaeacanthocephala

See also


Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Taxonavigation

Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Cladus: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Protostomia
Cladus: Spiralia
Cladus: Platyzoa
Phylum: Acanthocephala
Classes: Archiacanthocephala - Eoacanthocephala - Palaeacanthocephala - Polyacanthocephala

Name

Acanthocephala

References

  • Amin, O.M. 1987: Key to the families and subfamilies of Acanthocephala with the erection of a new class (Polyacanthocephala) and a new order (Polyacanthorhynchida). Journal of parasitology, 73: 1216–1219.
  • García-Varela, M.; Cummings, M.P.; Pérez-Ponce de León, G.; Gardner, S.L.; Laclette, J.P. 2002: Phylogenetic analysis based on 18S ribosomal RNA gene sequences supports the existence of class Polyacanthocephala (Acanthocephala). Molecular phylogenetics and evolution , 23: 288-292. PDF
  • García-Varela, M.; Pérez-Ponce de León, G.; de la Torre, P.; Cummings, M.P.; Sarma, S.S.S.; Laclette, J.P. 2000: Phylogenetic relationships of Acanthocephala based on analysis of 18S ribosomal RNA gene sequences. Journal of molecular evolution, 50: 532–540. PDF
  • Gordon, D.P. (ed.) 2009: New Zealand inventory of biodiversity. Volume 1. Kingdom Animalia. Radiata, Lophotrochozoa, Deuterostomia. Canterbury University Press, Christchurch, New Zealand.
  • Herlyn, H.; Piskurek, O.; Schmitz, J.; Ehlers, U.; Zischler, H. 2003: The syndermatan phylogeny and the evolution of acanthocephalan endoparasitism as inferred from 18S rDNA sequences. Molecular phylogenetics and evolution, 26: 155-164.
  • Near, T.J. 2002: Acanthocephalan phylogeny and the evolution of parasitism. Integrative and comparative biology, 42: 668-677. [1]
  • Near, T.J.; Garey, J.R.; Nadler, S.A. 1998: Phylogenetic relationships of the Acanthocephala inferred from 18S ribosomal DNA sequences. Molecular phylogenetics and evolution, 10: 287-298.

Vernacular names

Català: Acantocèfal
Česky: Vrtejši
Ελληνικά: Ακανθοκέφαλα
English: thorny-headed worms
Français: Acanthocéphales
Galego: Acantocéfalo
Magyar: Buzogányfejűek
Македонски: Боцкоглавци
Nederlands: haakwormen
日本語: 鉤頭動物
Polski: Kolcogłowy
Svenska: Hakmaskar
Wikimedia Commons For more multimedia, look at Acanthocephala on Wikimedia Commons.

Simple English

Acanthocephala
File:Acanthocephala
Scientific classification
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked) Bilateria
Superphylum: Platyzoa
Phylum: Acanthocephala (but see text)
Kohlreuther, 1771
Classes

Archiacanthocephala
Palaeacanthocephala
Eoacanthocephala

The Acanthocephala (Greek akanthos, thorn + kephale, head) are a group of parasitic worms. They may be called known as acanthocephales, thorny-headed worms, or spiny-headed worms. They have an evertable proboscis,[1] armed with spines, which they use to pierce and hold the gut wall of the host. Acanthocephalans have no gut and absorb nutrients directly from the host’s gut.

Acanthocephalans have complex life cycles, with various hosts, including invertebrates, fishes, amphibians, birds, and mammals. The juveniles are parasitic in crustaceans and insects. Adults live in the digestive tract of vertebrates, especially fish. About 1150 species have been described.[2]

The Acanthocephala were thought to be a separate phylum. Recent genome analysis has shown that they are closely related to rotifers. Since all parasites are derived from free-living forms, the Acanthocephalans are modified rotifers.[3] This is an example of molecular phylogenetics. In due course, spiny-headed worms will probably be placed in a taxonomic rank below phylum, such as sub-phylum or class.[4]

References

  1. This means: they keep the front part inside their body, until they push it out to pierce and hold the gut wall of their host.
  2. Ronald Shimek [1]
  3. 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. 
  4. Official ICZN website








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