Acanthocephala

Source: Wikipedia, the free encyclopedia.
For other uses, see Acanthocephala (disambiguation).

Acanthocephala
Temporal range: Late Cretaceous–Recent
Corynosoma wegeneri
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Clade: Bilateria
Clade: Nephrozoa
(unranked): Protostomia
(unranked): Spiralia
Clade: Gnathifera
Phylum: Acanthocephala
Koelreuter, 1771[1][2]
Classes

Acanthocephala

complex life cycles, involving at least two hosts, which may include invertebrates, fish, amphibians, birds, and mammals.[4][5][6][7] About 1420 species have been described.[8][9]

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.[10] This unified taxon is known as Syndermata
.

History

The earliest recognisable description of Acanthocephala – a worm with a proboscis armed with hooks – was made by Italian author

Joseph Koelreuter proposed the name Acanthocephala.[1] Philipp Ludwig Statius Müller independently called them Echinorhynchus in 1776.[1] Karl Rudolphi
in 1809 formally named them Acanthocephala.

Evolutionary history

The oldest known remains of acanthocephalans are eggs found in a coprolite from the Late Cretaceous Bauru Group of Brazil, around 70-80 million years old, likely from a crocodyliform. The group may have originated substantially earlier.[11]

Phylogeny

See also:
List of bilateral animal orders

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.

Seisonidea, producing the names and relationships shown in the cladogram
below.

Syndermata

Seisonida

The three rotifer classes and the Acanthocephala make up a clade called Syndermata.[12][4] This clade is placed in the Platyzoa.

A study of the gene order in the mitochondria suggests that Seisonidea and Acanthocephala are sister clades and that the Bdelloidea are the sister clade to this group.[13]

Currently the phylum is divided into four classes –

Polyacanthocephala and Eoacanthocephala. The monophyletic Archiacanthocephala are the sister taxon of a clade comprising Eoacanthocephala and the monophyletic Palaeacanthocephala.[14][4]

Morphology

Diagram of Acanthocephalan morphology
Some key features of acanthocephalan morphology

Several morphological characteristics distinguish acanthocephalans from other phyla of parasitic worms.

Digestion

Acanthocephalans lack a mouth or

intestines of their host and uptake nutrients which have been digested by the host, directly, through their body surface. The acanthocephalans lack an excretory system, although some species have been shown to possess flame cells
(protonephridia).

Proboscis

Cathayacanthus spinitruncatus[15]

The most notable feature of the acanthocephala is the presence of an

anterior, protrudable proboscis
that is usually covered with spiny hooks (hence the common name: thorny or spiny 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.[16]

Size

The size of these animals varies greatly, some are measured to be a few millimetres in length to

Polyploidy
is common, with up to 343n having been recorded in some species.

Skin

The body surface of the acanthocephala is peculiar. Externally, the skin has a thin

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.

Life cycles

A diagram of the life cycle of Polymorphus spp.

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.[4]

Reproduction

The Acanthocephala are

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

dorsally. The bell "swallows" the matured eggs and passes them on into the uterus. (Immature embryos are passed back into the body cavity through the dorsal opening.) From the uterus, mature eggs leave the female's body via her oviduct, pass into the host's alimentary canal and are expelled from the host's body within feces
.

Release

Adult Pomphorhynchus in a bluefish

Having been expelled by the female, the acanthocephalan egg is released along with the feces of the host. For development to occur, the egg, containing the acanthor, needs to be ingested by an arthropod, usually a crustacean (there is one known life cycle which uses a mollusc as a first intermediate host). Inside the intermediate host, the acanthor is released from the egg and develops into an acanthella. It then 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.

Host control

Thorny-headed worms begin their life cycle inside invertebrates that reside in marine or freshwater systems. Gammarus lacustris, a small crustacean that inhabits ponds and rivers, is one invertebrate that the thorny-headed worm may occupy. In recent years the occurrence of infections from these parasites have been increasing in Asian aquaculture practices.[17] This crustacean is preyed on 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 swims to the surface. 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 the bird, its final host.

Examples of this behaviour include the

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.[18]

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.

Human infections

In humans, it causes the disease

Macracanthorhynchus hirudinaceus from a child in Prague. Lindemann in 1865 reported that this organism was commonly isolated in Russia. The reason for this was discovered by Schneider in 1871 when he found that an intermediate host, the scarabaeid beetle grub, was commonly eaten raw.[20] The first report of clinical symptoms was by Calandruccio who in 1888 while in Italy infected himself by ingesting larvae. He reported gastrointestinal disturbances and shed eggs in two weeks. Subsequent natural infections have since been reported.[21] Eight species have been isolated from humans to date.[22] Moniliformis moniliformis is the most common isolate. Other isolates include Acanthocephalus bufonis and Corynosoma strumosum
.

See also

References

  1. ^
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  2. ^ Koelreuter, I. T. (1770). "Descriptio cyprini rutili, quem halawel russi vocant, historico-anatomica". Novi Commentarii Academiae Scientiarum Imperialis Petropolitanae. 15: 494–503.
  3. ^ "acanthocephalan". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  4. ^
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  8. ^ Freeman, Scott, Lizabeth Allison, Michael Black, Greg Podgorski, and Kim Quillin. Biological Sciences. 5th ed. Glenview, Il: Pearson, 2014. 638. Print.
  9. ^ Encyclopedia of Life, retrieved July 24, 2015
  10. ^ Shimek, Ronald (January 2006). "Nano-Animals, Part I: Rotifers". Reefkeeping.com. Retrieved July 27, 2008.
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  15. PMID 25331738. Open access icon
  16. ^ "Acanthocephalans drilling Acipenser stellatus intestine". Parasites World. Archived from the original on April 30, 2012. Retrieved August 3, 2009.
  17. S2CID 246297133
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  18. ^ Itämies, J.; Valtonen, E. T.; Fagerholm, H. P. (1980). "Polymorphus minutus (Acanthocephala) infestation in eiders and its role as a possible cause of death". Ann. Zool. Fenn. 17 (4): 285–289.
  19. S2CID 6120428
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  20. PMID 5090967
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  21. PMID 6827437
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  22. PMID 19689468
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Further reading

External links

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