PENTASTOMIDA, also called Linguatulida, a group of parasitic animals of uncertain systematic position but sometimes regarded as degenerate Arachnida (q.v.) of the order Acari. The body is worm-like, unsegmented, but superficially annulated, the alimentary canal traverses it from end to end, and close to the mouth, which is encircled by a horny ring, are two pairs of horny hooks. There are no special or gans of respiration or circulation and the nervous system con sists of a collar round the oesophagus and a pair of ventral strands. The sexes are distinct, the females are oviparous and the genera tive orifice in the males of all species and in the females of one genus, Reighardia, opens upon the ventral surface of the fore part of the body, whereas in the females of the others it is close to the anus.
There are three well marked types :—Reighardia, which has the genital orifice of both sexes opening anteriorly and the hooks be hind the mouth, is regarded as the representative of a special family, Reighardiidae. Only one species is known, namely, R. sternae, a parasite of terns and sea-gulls. Much better known are Linguatula (Pentastomum) and Porocephalus (Armillifer) as signed to the family Linguatulidae or Porocephalidae, which is characterised by the posterior position of the genital orifice in the females and the situation of the hooks nearly level with the mouth. Both these forms are of pathogenic importance to man. Lingua tula serrata (Pentastomum taenioides) is comparatively broad and flat and finely annulated. The male is less than an inch long, the
female considerably larger. When mature they live in the nasal cavities of dogs, wolves or foxes, and the ova, discharged in mucous secretion upon vegetation, may be swallowed by hares, rabbits, domesticated animals or man. The larvae, upon hatching in the stomachs of these intermediate hosts, make their way to the liver, kidneys, lungs or other visceral organs, there to remain encysted until the host is devoured by the canine carnivore into whose nasal chambers they pass to become adult and breed. The parasitic cycle is thus very like that of tape-worms.
Porocephalus (Armillifer) armillatus, larger than Linguatula, has the body cylindrical and marked by a series of upstanding, thick, rick-like ridges. The parasitic cycle is similar to that of Linguatula, but the hosts are different. The adults infest the lungs of African snakes, pythons (P. regius and P. sebae) and Puff adders (Bitis nasicornis). The eggs, disseminated by these rep tiles, are taken up in water or vegetable food by a great variety of animals, by negroes, monkeys, ungulates, hedgehogs and even lions and leopards, in whose viscera the immature forms have been found encysted. Infection of the lungs or other important inter nal organs in man by this parasite may be followed by serious pathological results. (R. I. P.)