Monogononta Acanthocephala The three rotifer classes and the Acanthocephala make up a clade called Syndermata. 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. The monophyletic Archiacanthocephala are the sister taxon of a clade comprising Eoacanthocephala and the monophyletic Palaeacanthocephala. Digestion[ edit ] Acanthocephalans lack a mouth or alimentary canal.
This is a feature they share with the cestoda tapewormsalthough 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 paraziți acantocefalici. The acanthocephalans lack an excretory system, although some species have been shown to paraziți acantocefalici flame cells protonephridia.
Scanning electron microscopy of proboscis of Cathayacanthus spinitruncatus  The most notable feature of the acanthocephala is the presence of an anteriorprotrudible proboscis paraziți acantocefalici 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 paraziți acantocefalici 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 The whole proboscis apparatus can also be, at least partially, withdrawn into the body cavity, and this is effected by two retractor muscles which run from the posterior aspect of the septum to the body wall.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.
A curious feature shared by both larva and adult is the large size of many of the cells, e. Polyploidy is common, with up to n having been recorded in some species. Skin[ edit ] The body surface of the acanthocephala is peculiar. Externally, the skin has a thin tegument covering the epidermiswhich consists of a syncytium with no cell walls.
Paraziți acantocefalici syncytium is traversed by a series of branching tubules containing fluid and is controlled paraziți acantocefalici 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[ edit ] Paraziți acantocefalici central ganglion of the nervous system lies behind the proboscis sheath or septum.
acantocefali — с русского на все языки
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 paraziți acantocefalici is also a genital ganglion. Some scattered papillae paraziți acantocefalici possibly be sense-organs. Life cycles[ edit ] 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.
Reproduction[ edit ] The Acanthocephala are dioecious an individual organism is either paraziți acantocefalici or female.
🎓 viermi intestinali 🧬
There is a structure called the genital ligament which runs from the posterior end of the proboscis sheath to the paraziți acantocefalici 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, paraziți acantocefalici the testes, as paraziți acantocefalici bodies along the ligament. From the ovaries, masses of ova dehisce into the body cavity, floating in its fluids for fertilization paraziți acantocefalici male's sperm. After fertilization, each egg contains a developing embryo. These embryos hatch into first stage larva.
The fertilized eggs are brought into the uterus by actions of the uterine bell, a funnel like opening continuous with the uterus. At the junction of the bell and the uterus there is a second, smaller opening situated hpv impfung vortrag. The bell "swallows" the matured eggs and passes them on into the uterus.
Sinonimele și antonimele Acantocefali în dicționarul de sinonime Italiană
Immature embryos paraziți acantocefalici passed back into the body cavity through the dorsal opening. From the uterus, mature eggs leave the female's body via her oviductpass into the host's alimentary canal and are expelled from the host's body within feces. Adult Pomphorhynchus in a bluefish Having been expelled by the female, paraziți acantocefalici acanthocephalan egg is released along with the feces of the host.
For development to occur, the egg, containing the acanthorneeds to be ingested by an paraziți acantocefaliciusually 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.
acantocefal - Wikționar
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 tab anthelmintic by a suitable final host, the cycstacant excysts, everts its proboscis and pierces the gut wall.
It then feeds, grows and develops its sexual paraziți acantocefalici. 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[ edit ] Thorny-headed worms begin their life cycle inside invertebrates that reside in marine or freshwater systems.