J. Riley

The biology of pentastomids.

Publisher Summary This chapter describes the biology of pentastomids and several of the most important deficiencies are outlined. Pentastomids, otherwise known as linguatulids or tongueworms, are a relatively neglected and poorly understood class of endoparasites, which occupy a unique position among invertebrates in that, as adults, they are entirely restricted to the respiratory tract of vertebrates: the majority of species grow to maturity in the lungs. About 90% of species infect reptiles, and it is probable that they have been associated with these hosts since the Mesozoic. Despite this long period for potential adaptive radiation, the basic body design is remarkably conservative, and pentastomids comprise a homogeneous and distinctive systematic assemblage of about 100 species. All possess a vermiform, often conspicuously annulated abdomen, usually strongly united with a rounded cephalothorax, which bears, on its ventral surface, a small sucking mouth flanked by two pairs of hooks. Pentastomids, in common with other parasites, are regulators of host populations and many of the species recovered from zoo autopsies. In some cases, host death is directly or indirectly attributable to a pentastomid infection.

A revision of the taxonomy of the blunt-hooked Raillietiella, pentastomid parasites of African, South-East-Asian and Indonesian lizards, with a description of a new species

SummaryThree species of Raillietiella with blunt tips to the posterior hooks have been described from south-east Asia and Indonesia. However, we have established that two other species. R. hemidactyli from an Indian agamid lizard and R. mabuiae from an African skink, also possess blunt hooks but this fact is unaccountably not mentioned in early descriptions. The various species are distinguished by differences in body-length, or number of abdominal annuli and/or host and geographical distribution. Certain of the morphological characters overlap and some authors have considered the complex a single species. We have examined preserved material from a variety of sources, including type specimens, and by using comparative hook data and a standardized annulus counting procedure we show that at least three of the earlier described species are valid. A new species, R. frenatus, is described. An attempt is made to correct the various errors in identification that have crept into the more recent literature. ac]19801204

On the systematics and life-cycle of the pentastomid genus Kiricephalus Sambon, 1922 with descriptions of three new species

SummaryThe three previously described Kiricephalus spp. are considered distinct because of differences in the number of abdominal annuli and differences in geographical and host distribution. Observations of a large number of specimens have confirmed the validity, and considerably extended the host list, of the two most common species, K. pattoni (Stephens, 1908), Sambon, 1922 and K. coarctatus (Diesing, 1850), Sambon, 1910. Generally annulus number is a satisfactory and reliable criterion upon which to separate species and three new species are described. One, K. constrictor, has an overlapping geographical distribution and annulus count with K. coarctatus, but comparative hook data reveals that they are unrelated. The life-cycles of the genus, reappraised in the light of the present findings, are shown to involve three vertebrate hosts. Eggs are only infective to amphibians, saurians or mammals, and snakes are second intermediate and definitive hosts, the final infection being acquired through ophiophagy. ac]19790725

Experimental life-cycle studies of Raillietiella gehyrae Bovien, 1927 and Raillietiella frenatus Ali, Riley and Self, 1981: pentastomid parasites of geckos utilizing insects as intermediate hosts

The life-cycles of two closely related cephalobaenid pentastomids, Raillietiella gehyrae and Raillietiella frenatus, which utilize geckos as definitive hosts and cockroaches as intermediate hosts, have been investigated in detail. Early development in the fat-body of cockroaches involves 2 moults to an infective, 3rd-stage larva which appears from 42–44 days post-infection. Complete development in geckos involves a further 5 moults in the case of males and 6 for females. Males mature precociously and copulation is a once-in-a-lifetime event which occurs around day 80 post-infection when both sexes are the same size but the uterus of the female is undeveloped. Sperm, stored in the spermathecae, is used to fertilize oocytes which slowly accumulate in the developing saccate uterus. Patency commences when the uterus carries approximately 4000–5500 eggs but only 25–36 % of these contain fully developed primary larvae. Since only mature eggs are deposited, we postulate that the vagina (?) of the female must be equipped with a selective filter that allows through large eggs but retains smaller, immature eggs. Thus the only limit on fecundity is the total number of sperms in the spermathecae and this is precisely the same factor that constrains egg production in the advanced order Porocephalida.

The phylogenetic relationships of the pentastomida: The case for their inclusion within the crustacea

Abstract Pentastomids are a distinct systematic assemblage of worm-like animals which, as adults, are parasitic in the respiratory tracts of vertebrates. Recent evidence regarding the phylogenetic affinities of the group is assessed. Evidence favouring a descent from annelids, or from an annelid-like ancestor of the arthropods, is dismissed because it is based on gross comparative anatomy and fails to take into account the many adaptive features of these highly specialised endoparasites. Theories according pentastomids the status of an independent phylum, sharing a similar rank with tardigrades and onychophorans are dismissed similarly. Three crucial items of evidence, embryogenesis, the structure of the integument, and gametogenesis are considered to confirm previous hypotheses of genuine arthropod homologies. Spermatogenesis particularly, clearly establishes pentastomids as a crustacean sub-class, closely allied to the Branchiura. We postulate that the pentastomid progenitor was originally a parasite of fish which subsequently became adapted to an endoparasitic existence in aquatic reptiles through predation.

On the systematics of the pentastomid genus Porocephalus (Humboldt, 1811) with descriptions of two new species

SummaryBy using comparative hook measurements and a standardized annulus counting procedure we have shown that the three previously described American species of Porocephalus are distinct. However there is little to relate these to the two African species since they differ in several aspects of their morphology and life-cycles. Two new species are described from North and Central American rattlesnakes and these are distinguished from P. crotali (Humboldt, 1808) by their size and hooks. P. stilesi (Sambon, 1910) is specific to snakes of the genus Lachesis. Another possible new species, closely related to P. clavatus (Wyman, 1847) infects snakes of the genus Bothrops: it is not P. stilesi as previously supposed. The life-cycles of Porocephalus spp. are discussed.

An experimental investigation of a direct life-cycle in Reighardia sternae (Diesing, 1864), a pentastomid parasite of the herring gull ( Larus argentatus )

A direct life-cycle in Reighardia sternae, a cephalobaenid pentastomid of gulls was investigated: the work was prompted by a report of eggs and larvae recovered from the stomach and intestine of a naturally infected gull. Infective pentastomid eggs were obtained by surgically transplanting maturing female Reighardia, taken from freshly shot wild gulls, into captive recipients. Faecal material from birds thus artificially infected was collected daily and examined for eggs. Eggs were force fed to 33 hand-reared (from eggs or nestlings) juvenile gulls which were selected at random and sacrificed at intervals thereafter and examined for pentastomids. One hour after infection, primary larvae appear in the body cavity where they moult immediately. They grow steadily and by 27-35 days are sexually differentiated, and by 66 days have copulated. Fertilized females take a further 116 days to produce eggs by which time they are 7-6 cm long. The complex migrations undertaken by developing larvae in the gull, and the problems of the mechanism of direct transmission, are discussed.

A revision of the taxonomy of pentastomid parasites (genusRaillietiella Sambon, 1910) from American snakes and amphisbaenians

SummaryTwo species of pentastomid belonging to the genusRaillietiella Sambon, 1910 have been described from American snakes although their characters overlap and they are only differentiated on criteria now known to be unreliable (Self, 1969). We show that the species can be readily distinguished on the sole criterion of the form of the male copulatory spicule. There is confusion in many of the early records about hosts. After untangling these records, as far as possible, we postulate that the two species have allopatric distributions, one being Neotropical and the other Nearctic. A new species,R. crotali, is described, which is close to the Neotropical speciesR. furcocera, but it has much smaller hooks. Closely related species from the Old World utilize vertebrates as intermediate hosts and this is almost certainly true of the species described here. Given this, the very considerable differences in dietary regimen of the various hosts harbouring ‘R. furcocerca’, strongly suggest that there may be more than one species involved. R. gigliolii from the South American amphisbaenianAmphisbaena alba is also described since, historically, it has been confused withR. furcocerca. The systematics of these snake and amphisbaenian raillietiellids is discussed. ac]19821203

An experimental investigation of the development of Porocephalus crotali (Pentastomida : Porocephalida) in the western diamondback rattlesnake (Crotalus atrox)

Abstract The development of Porocephalus crotali in the rattlesnake definitive host ( Crotalus atrox ) is described. Infective nymphs excyst, penetrate the body cavity by boring through the stomach mucosa, and, in as little as 12 days, enter the lung where they grow to maturity. Copulation, which was observed at 75 and 86 days post-infection, is followed by prolonged sperm storage in spermathecae. This heralds a long prepatent period. Egg production, commencing 230–250 days after infection, is massive and continuous over a lifetime of several years. Hook data indicates that at least three moults separate the infective nymph and the adult female making a minimum of nine for the complete development from the primary larva. There was little evidence of pathological symptoms.

Observations on the osmoregulatory system of pentastomids: The tegumental chloride cells

Abstract The chitinous procuticle of pentastomids is permeated by small pores which communicate with specialized epidermal cells previously termed cuticular cells. Ultrastructural evidence is presented which suggests that these cells are concerned with the regulation of the hydromineral balance of the haemolymph. Probably all pentastomids regulate hypo-osmotically: that is they maintain a blood concentration which is lower than that of their host. Since pentastomids feed on host blood or lymph which is rich in sodium and chloride, it suggested that chloride cells secrete excess ions. The extent to which chloride cells must concentrate ions depends upon the nature of the food, the rate of exosmosis and the rate of salt gain by diffusion.