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PENTASTOMIDA, or LINGUATULINA
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See also:PENTASTOMIDA, or LINGUATULINA , vermiform entoparasitic animals, of which the exact zoological position is unknown, although they are usually regarded as highly modified degenerate See also:Arachnida of the See also:order Acari. The See also:body is sub-cylindrical or somewhat See also:convex above, flatter below, broad and See also:oval in front and narrowed and elongate behind. Its integument is marked by a large number of transverse grooves simulating the segmentation of Annelids, and near the anterior extremity See also:close to the mouth are two pairs of recurved chitinous hooks. The alimentary See also:canal is a See also:simple See also:tube traversing the body from end to end, the anus opening at the extremity of its narrowed tail-like termination. The See also:nervous See also:system is represented by an oesophageal See also:collar and a suboesophageal ganglion, whence paired nerves pass outwards to innervate the anterior extremity and backwards towards its posterior end. No See also:respiratory or circulatory See also:organs are known. The sexes are distinct but dissimilar in See also:size, the See also:female being usually much larger than the male. The generative organs occupy a large See also:part of the body cavity. In the female the ovary is a large unpaired See also:organ from the anterior end of. which arise two oviducts, and connected with the latter are a pair of large so-called copulatory pouches, which perhaps See also:act as receptacula seminis. These and the oviducts See also:lie on the anterior See also:half of the body; but the oviducts themselves soon unite to See also:form a single tube of See also:great length, which runs backwards to its posterior extremity, terminating in the genital orifice close to the anus. In the male, on the contrary, this orifice is situated in the anterior half of the body, not far behind the mouth. The orifice leads into a large pouch lodging a pair of very See also:long penes, which are coiled up when not in use. The two testicles, which extend far back into the posterior part of the body, are long and tubular. Anteriorly their See also:vasa deferentia soon unite into a See also:common duct, which opens into the pouch containing the penes. Also communicating with this pouch is a pair of long slender flagelliform tubes, of which the See also:function is unknown. The structure of the adult Linguatula or Pentastomum, above described, does not See also:supply convincing See also:evidence of relationship with the Acari. At the same See also:time some Acari, like Eriophyes (Phytoptus) and Demodex, have the body elongated and annulated, but In these See also:groups the See also:elongation of the body is caudal or See also:post-anal, as is attested by the position of the anus far forwards on its ventral See also:surface. Again, the adult Pentastomum shows no trace of appendages, unless the two pairs of chitinous hooks are to be regarded as the vestiges of jaws or See also:ambulatory limbs. In the embryo, however, what have been regarded as remnants of limbs may be seen. In the mature See also:stage Pentastomida live in the respiratory passages of See also:mammalia, principally in the nasal cavities. The remarkable See also:life-See also:history of one See also:species, Linguatula taenioides, has been worked out in detail and presents a close See also:analogy to that of some Cestodes. The adults live in the See also:nose of See also:dogs, where they have been known to survive over fifteen months. Each female See also:lays a vast number of eggs, about 500,00o being the estimated amount. These are expelled along with mucus by the See also:sneezing of the See also:host. If they fall on pasture See also:land or See also:fodder of any See also:kind and are eaten by any herbivorous See also:animal, such as a See also:hare, See also:rabbit, See also:horse, See also:sheep or ox, the active embryos or larvae are set See also:free in the alimentary canal of the new host. These larvae are See also:minute oval creatures with a comparatively See also:short apically fringed caudal prolongation and furnished with two pairs of short two-clawed processes, which may represent the limbs of anthropods and possibly the two pairs of legs found in Acari of the See also:family Eriophyidae. The larva is also armed anteriorly with a median piercing probe and a pair of See also:sharp hooks by means of which it perforates the walls of the alimentary See also:tract and makes its way into the body cavity, lungs or See also:liver. Here it becomes encysted, and losing its See also:boring apparatus and claw-bearing processes remains for a time quiescent. After a See also:series of moults it passes into the second larval stage, somewhat like the See also:parent but differing in having each integumental See also:ring armed with a fringe of backwardly directed short bristles. This sexually immature stage, regarded at one time as representing a distinct species and named Linguatula denticulata, is reached in about six or seven months and See also:measures from 6 to 8 mm. in length. In the event of the host escaping being killed and eaten it is believed that some of these larvae wander about or ultimately make their way to the exterior, possibly through the bronchi; nevertheless it seems to be certain that they can only reach sexual maturity in the nasal passages of some carnivorous animal, and the See also:chance of attaining this environment is afforded when the viscera of the host are devoured by some flesh-eating mammal. The adult female of L. taenioides measures about 4 in. long and the male barely one-See also:fourth of that. The adult and immature stages are, however, by no means confined respectively to carnivorous and herbivorous species of mammals. The adult stage, for example, has been found in the nasal passages of sheep, goats,horses and even of See also:man, and the larval stage in the pleural and peritoneal cavities of dogs and See also:cats. (R. I. Additional information and CommentsThere are no comments yet for this article.
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