The endohelminth component communities of creek chub (Semotilus atromaculatus) were studied in southeastern Nebraska to determine whether parasite community similarity corresponded to drainage identity. Creek chub were sampled from 12 sites on 3 drainages of the Big Nemaha River system during 4 periods from summer 2003 to summer 2005. Analysis of similarity, cluster analyses, and ordination suggested that community similarity was more similar among sites within drainages than among drainages. Vector analysis and indicator species analysis demonstrated that the distributions of 2 of the parasite species, Paulisentis missouriensis (Acanthocephala) and Rhabdochona canadensis (Nematoda), were highly aggregated among drainages. Allocreadium lobatum (Trematoda) and Proteocephalus sp. (Cestoda) occurred more uniformly among sites and drainages. Procrustean analyses suggested that drainage-level differences in species composition better explained the spatial pattern of community similarity than did physical distance. These results suggest that there are predictable differences in component communities among drainages.

We investigated the effects of helminth endoparasite load on the physiological performance of 2 sympatric fishes, Lepomis macrochirus and Lepomis megalotis (Centrarchidae). Species-specific swimming endurance and thermal tolerance were used as measures of physiological performance. A discriminant function analysis for endurance indicated that only kidney parasite load significantly correlated with the first discriminant function. However, overall increases in parasite load within the mesentery, heart, liver, and small intestine were each associated with observed decreases in endurance for both species. A discriminant function analysis also indicated that increases in mesentery and liver parasite load were significantly correlated with decreases in thermal tolerance. An overall increase in parasite load within the mesentery, heart, liver, small intestine, and spleen was also correlated with decreased thermal tolerance. Thus, our results suggest that helminth endoparasite load may play an important role in the physiological performance of these sympatric fishes. Differences in microhabitat utilization and partitioning of L. macrochirus and L. megalotis correlate with species-specific physiological performance. For example, microhabitats with greater current velocities are used by L. megalotis because of the greater capacity of this species for endurance. However, parasite loads that significantly reduce endurance would force changes in habitat utilization causing direct competition among species normally partitioned. We offer a theoretical discussion of how parasite load may create opportunities for interaction and competition among individuals and species usually partitioned by physiologically based preferences in microhabitat utilization.

Ictalurid catfishes represent a family of freshwater fishes exclusively North American in distribution. The Balsas catfish, Ictalurus balsanus, is endemic to the Balsas River drainage in central Mexico, which flows to the Pacific Ocean. In this article we present the helminth fauna of this catfish through a survey along its distributional range in the Balsas River basin. Between December 2003 and May 2006, 148 specimens of I. balsanus were collected from 10 localities in the Balsas River drainage. In total, 10 species of helminths were found, including 2 digeneans, 2 cestodes, and 6 nematodes. These parasites correspond to 4 larval forms (Eustrongylides sp., Contracaecum sp., Serpinema trispinosum, and Clinostomum complanatum) and 6 adults (Creptotrema agonostomi, Rhabdochona canadensis, Dichelyne (Dichelyne) mexicanus, Raillietnema kritscheri, Megathylacoides lamothei, and Monticellidae gen. sp.). The results are used to address some biogeographical aspects, particularly the concept of core parasite faunas and parasite faunal exchange in a transitional area.

Thelastoma krausi n. sp. is described based on specimens from the hindgut of Euryurus leachii (Gray, 1832) collected in central Ohio, U.S.A. Females of this species have the excretory pore located at the point of the esophageal bulb and have a longer tail than that of several other species. In comparison to species that also share these characters, no other species shares similar anatomical dimensions. In most similar species, the female esophageal length is longer than that of T. krausi n. sp. The female tail length is also longer than that of many similar species. The males of T. krausi n. sp. lack lateral alae and have an arrangement of papillae around the genital cone, including only a single postcloacal papilla, which varies from that of other described species.

Parachristianella parva sp. nov. is described from the spiral valve of Urobatis maculatus Garman, 1913 from the Gulf of California, Mexico. The new species is distinguished by its small size and small number of testes per segment (8–10). Parachristianella trygonis Dollfus, 1946 is reported from the spiral valve of Mobula munkiana Notarbartolo di Sciari, 1987 and from Dasyatis brevis (Garman, 1880), whereas the adult of Parachristianella dimegacantha Kruse, 1959 is described for the first time from the spiral valves of Urotrygon simulatrix Miyake and McEachran, 1988; Sphyrna zygaena (Linnaeus, 1758); and Dasyatis longus (Garman, 1880), all from the Gulf of California.

Cetitrema meadi sp. n. (Trematoda: Nasitrematinae), a liver fluke from Gervais' beaked whale (Mesoplodon europaeus), is described. This species is easily distinguished from the one other member of the genus by the size and shape of body and testes. Lecithodesmus spinosus, Margolis and Pike, 1955, described from the bile ducts of Balaenoptera physalus, is transferred to the genus Brachycladium, e.g., Brachycladium spinosus (Margolis and Pike, 1955) n. comb., and is reported as a new host record from the sperm whale (Physeter macrocephalus Linnaeus, 1758). Additional new host and distribution records are reported for the liver flukes, Oschmarinella sobolevi Skrjabin, 1947, Brachycladium pacificum (Dailey and Perrin, 1973) Gibson, 2005, and Brachycladium sp., from 3 species of cetaceans, Mesoplodon europeaeus, Globicephala macrorhynchus, and Ziphius cavirostris, respectively.

Hippocrepis myocastoris Babero, Cabello et Kinoed, 1979 is redescribed from a naturally infected Myocastor coypus Molina (Rodentia: Myocastoridae) captured in the Negro River (40°07′S; 64°27′W) from Patagonia, Argentina. A total of 31 ovigerous specimens were stained and measured. These specimens of H. myocastoris were similar to paratype in morphology and morphometric characteristics, did not have ventral gland, and mature eggs presented 4 polar filaments on opercular pole. This is the first record of a notocotylid parasitizing aquatic rodents in Argentinean Patagonia.

In a survey of mammals from Paraguay, 3 species, Artibeus lituratus, the great fruit-eating bat, Tolypeutes matacus, the southern 3-banded armadillo, and a Tolypeutes sp. were found to be infected with oligacanthorhynchid acanthocephalans. Artibeus lituratus harbored Neoncicola artibei n. sp., which differs from its congeners in the number and morphology of the hooks of the proboscis armature. The generic diagnosis of Neoncicola has been emended accordingly. Oligacanthorhynchus carinii Travassos, 1916 was found in T. matacus and an oligacanthorhynchid cystacanth in Tolypeutes sp. Previous arguments that the concept of Oligacanthorhynchus should be restricted to species from bird hosts and the concept of Hammaniella be reinstated for species infecting mammals could not be addressed using the data presently available.

Six species of acanthocephalans were collected from 30 of 62 surveyed species of fish in Lake Biwa, the most ancient lake in Japan, and from various water bodies in the lake's drainage basin including the Seta and Daido Rivers. The 3 most common species were Acanthocephalus opsariichthydis Yamaguti, 1935 (8 new host records), Echinorhynchus cotti Yamaguti, 1935 (7 new host records), and Pseudorhadinorhynchus samegaiensis Nakajima and Egusa, 1975 (7 new host records; perhaps endemic to Lake Biwa and its basin). The latter 2 species were found only in the spring. Specimens of both species were also found in Gymnogobius isaza (Tanaka, 1916) in the autumn. Gravid females of all 3 species were found in the spring. Developed cystacanths of Southwellina hispida (Van Cleave, 1925) Witenberg, 1932 were also collected (5 new host records). Anatomical similarities between these species and the original descriptions are clearly evident, but differences in certain key characteristics are noted. Two recently described species of Acanthogyrus (Acanthosentis) Verma and Datta, 1929, Acanthogyrus (Acanthosentis) alternatspinus Amin, 2005, and Acanthogyrus (Acanthosentis) parareceptaclis Amin, 2005 were also first collected in the course of this survey. Three species previously recorded in the 1920s and 1930s from Lake Biwa were not found in the present survey: Acanthocephalus aculeatus Van Cleave, 1931, Acanthocephalus gotoi Van Cleave, 1925, and Echinorhynchus parasiluri Fukui, 1929.

Hemidactylus frenatus is reported as a host for the pentastome parasites Raillietiella frenatus and Waddycephalus sp. in Australia for the first time. Both adult and nymphal pentastomes were found to infect H. frenatus collected in the Northern Territory and surrounding islands but were absent in North Queensland. Raillietiella frenatus, reported from H. frenatus throughout Southeast Asia and the Pacific Islands, is also reported in Australia for the first time. A single specimen of a female Raillietiella sp., corresponding to the measurements for R. frenatus, is reported from the native gecko Gehyra australis. Raillietiella frenatus has been reported transferring between host species in other locations where H. frenatus has been introduced. The need for further study of the pentastome parasites of geckoes in northern Australia to determine the spread of R. frenatus is emphasized.

Xenentocleidus n. g. (Monogenoidea: Dactylogyridae) is proposed for Xenentocleidus xenentodoni (Jain, 1961) n. comb. (jr syn. Urocleidus xenentodoni Jain, 1961) collected from the gills of a freshwater garfish, Xenentodon cancila (Hamilton, 1822), in the River Gomti and Sai, Lucknow, Uttar Pradesh, India. The new genus is characterized by species with a dextroventral vagina with distally lightly sclerotized funnel-shaped vestibule and proximally highly sclerotized tube, a coiled copulatory tube with counterclockwise ring(s), a grooved, sheathlike accessory piece, rod-shaped haptoral bars, and a ventrally striated tegument at the region of copulatory complex. Xenentocleidus appear to be a sister group of Sclerocleidoides Agarwal, Yadav and Kritsky, 2001 on the basis of the following: a coiled male copulatory tube with counterclockwise coil(s), a ventral vaginal pore, and a subhexagonal haptor, armed with dorsal and ventral anchor/bar complexes, and 7 pairs of hooks.

Sixteen species of both native and alien fish were collected and examined for monogenoids from September 2001 to March 2004 in bodies of water located within fishing areas of the Po River (northern Italy). A checklist of monogenoids was compiled and integrated with literature reports of Italian monogenoids, updating the number of known Italian freshwater monogenoids to 35, with 15 new host or locality records (or both). Parasitological data of monogenoids on native and alien demonstrate the ability of alien monogenoids to colonize native hosts. The process of invasion of nonnative monogenoids in Italy started about 30 yr ago and is still ongoing: 17 of the 35 monogenoids now present in Italian freshwaters are considered alien (5 species of monogenoids arrived in Italy from America, 11 from Central Europe, and 1 from Eurasia), 2 are considered native, and the remaining 16 are considered of unknown origin because of our limited knowledge concerning the original distribution of monogenoids.

Geneiorhynchus manifestus n. sp. (Apicomplexa: Eugregarinida) is described from the naiads of Anax junius (Odonata: Aeshnidae) collected from the Big Sandy Creek Unit of the Big Thicket National Preserve, Polk County, Texas, U.S.A. The genus Geneiorhynchus is revised and its constituent species reviewed. Descriptions are provided for 2 previously named species, Geneiorhynchus monnieri from naiads of Libellula depressa (Odonata: Libellulidae) collected from Bayreuth, Germany and Roscoff, France and Geneiorhynchus aeshnae from naiads of Aeshna constricta and Aeshna sp. (Odonata: Aeshnidae) collected from Pennsylvania, U.S.A., and Cheboygan County, Michigan, U.S.A.; and 3 previously reported taxa recognized as new species: Geneiorhynchus desportesi n. sp. from naiads of Aeshna cyanea (Odonata: Aeshnidae) collected from Montpellier, France, Geneiorhynchus baudoini n. sp. from naiads of Aeschna grandis (Odonata: Aeshnidae) collected from Vincennes and Besse-et-Saint Anastaise, France, and Geneiorhynchus shteini n. sp. from naiads of Aeshna cyanea and Aeshna sp. (Odonata: Aeshnidae) collected from Lakes Pert and Svyat, Karelian Republic, Russian Federation and both Hersbruck and Bamberg, Germany.

Nubenocephalus secundus n. sp. (Apicomplexa: Eugregarinida) is described from adults of Argia sedula (Odonata: Zygoptera: Coenagrionidae) collected from Harmon Creek, Sam Houston State University Center for Biological Field Studies, Walker County, Texas, U.S.A. This is the second species described in the genus and confirms the generic hypothesis of Nubenocephalus. The generic diagnosis of Nubenocephalus is revised to reflect common characters of its constituent species and a previously described Asian gregarine, Nubenocephalus mutabilis n. comb. (=Ancyrophora mutabilis) is recognized as a member of the genus.

During the summers of 2000, 2001, and 2002, 1,950 fecal samples from 4 families, 10 genera, and 16 species of rodents in Alaska, U.S.A. (N = 1,711), and Siberia, Russia (N = 239) were examined for coccidia (Apicomplexa: Eimeriidae). The 4 families sampled were Dipodidae (jumping mice), Erethizontidae (New World porcupines), Muridae (mice, rats), and Cricetidae (voles, lemmings). Nineteen oocyst morphotypes were observed, of which 10 were consistent with descriptions of known coccidia species from murid hosts, 8 were similar to oocysts described previously from other genera than those in which they are found here (and are called Eimeria species 1–8), and 1 is described as new. In the Dipodidae, all from Alaska, 0/15 Zapus hudsonius had coccidian oocysts in their feces when examined. In the Erethizontidae, all from Alaska, 0/5 Erethizon dorsatum had oocysts when examined. In the Muridae, all from Russia, 0/5 Apodemus peninsulae had oocysts when examined. In the Cricetidae from Alaska, we found the following infections: 15/72 (21%) Lemmus trimucronatus (Eimeria spp. 3, 4, 5); 10/29 (34%) Microtus longicaudus (Eimeria saxei, Eimeria wenrichi); 41/88 (47%) Microtus miurus (Eimeria coahiliensis, Eimeria ochrogasteri, Eimeria saxei, Eimeria wenrichi); 278/405 (68%) Microtus oeconomus (E. ochrogasteri, E. saxei, E. wenrichi); 116/159 (73%) Microtus pennsylvanicus (E. saxei, E. wenrichi); 9/52 (17%) Microtus xanthognathus (E. wenrichi); 218/699 (31%) Myodes rutilus (Eimeria cernae, Eimeria gallati, Eimeria marconii, Isospora clethrionomydis, Isospora clethrionomysis, and a new Eimeria species); 34/187 (18%) Synaptomys borealis (Eimeria spp. 6, 7, 8, Eimeria synaptomys). In the Cricetidae from Siberia, we found the following infections: 5/24 (21%) Alticola macrotis (Eimeria spp.1, 2); 0/5 Dicrostonyx torquatus; 1/11 (9%) Lemmus lemmus (Eimeria sp. 3); 30/48 (52%) Mi.oeconomus (E. saxei, E. wenrichi); 5/53 (9%) Myodes rufocanus (E. cernae, E. gallati, I. clethrionomydis, the new Eimeria sp.); 21/85 (25%) Myodes rutilus (E. cernae, E. gallati, E. marconii, the new Eimeria sp.); 0/8 Myopus schisticolor. Oocysts of

During the spring, summer, and fall of 2003 and 2004, 947 and 1,970 Planorbella trivolvis (=Helisoma trivolvis) collected from 1 site in Portage County, Wisconsin, U.S.A., were measured and examined for larval trematodes. Cercarial morphology was used to identify trematode larvae, and the prevalence of each larval type was determined. Totals of 292 and 618 larval trematode infections, including 140 and 191 identified as Ribeiroia ondatrae, were observed in 2003 and 2004, respectively. In addition to R. ondatrae, collections yielded 8 morphologically distinct larvae: echinostome, armatae, magnacauda, amphistome, cystophorous, longifurcate-pharyngeate/strigea, brevifurcate-pharyngeate/clinostomoid, and brevifurcate-apharyngeate. Ribeiroia ondatrae and echinostome larvae contributed 30.9% and 25.2%, respectively, of the overall trematode prevalence observed in 2004, whereas magnacauda, cystophorous, longifurcate-pharyngeate, brevifurcate-pharyngeate, and brevifurcate-apharyngeate infections were only infrequently encountered. Because the prevalence of R. ondatrae might have implications for the genesis of amphibian malformations in the field, the focus of this study was to determine how the prevalence of R. ondatrae fluctuates with time. In both 2003 and 2004, the total intramolluscan trematode prevalence, as well as that of R. ondatrae and echinostome larvae, increased significantly from spring to fall. These results were reaffirmed in an analysis of snail size and trematode prevalence, which showed that intramolluscan prevalence increased from spring to fall within all size classes. However, unlike the prevalence of echinostome larvae, the prevalence of R. ondatrae exhibited a midsummer decline before rising rapidly in late September and October.

Boron compounds are increasingly recognized as important industrial pollutants. We examined whether elevated concentrations of boron would exert toxic effects on different life cycle stages of the rodent gastrointestinal nematode Heligmosomoides bakeri and established toxicity in feeding and nonfeeding stages. All stages except eggs responded in a dose-dependent manner to boron. Reduced motility of first-stage larvae immediately after hatching and of the larvae exposed to boron only at the third larval stage were observed. Moreover, exposure of third-stage larvae to high concentrations of boron reduced their infectivity to mice. Survival of first- and second-stage larvae and of fourth-stage larvae and adults cultured in vitro in boron was impaired. Interestingly, adult males were more sensitive to boron than adult females. Finally, per capita fecundity of females cultured in vitro decreased with increasing boron concentration. Together, these results show that high boron concentrations are harmful to free-living stages and to parasitic stages in vitro and support our hypothesis that nonfeeding stages (eggs and third-stage larvae) are more resistant to boron than feeding stages (first-, second-, and fourth-stage larvae and adult worms).

Forty-three frogs representing 6 species (Dendropsophus cachimbo, Scinax fuscomarginatus, Leptodactylus fuscus, Leptodactylus martinezi, Leptodactylus mystaceus, and Leptodactylus rhodomystax) and 35 lizards representing 3 species (Kentropyx calcarata, Leposoma osvaldoi, and Potamites ecpleopus) collected in the Brazilian state of Pará were examined for helminths. One species of Trematoda, Brachycoelium salamandrae, and 12 species of Nematoda, adults of Capillaria recondita, Cosmocerca brasiliense, Cosmocerca podicipinus, Falcaustra belemensis, Falcaustra maculata, Kentropyxia sauria, Oswaldocruzia vaucheri, Physaloptera retusa, Schrankiana formulosa, Schrankiana fuscus, Schrankiana schranki, and juveniles of Acuariidae gen. sp., were found. Only B. salamandrae occurred in both frogs and lizards. There were 1.53 ± 0.13 (x ± 1 SE) helminth species/infected frogs and 28.52 ± 11.7 helminth individuals/infected frogs and 1.12 ± 0.08 helminth species/infected lizards and 6.47 ± 1.58 helminth individuals/infected lizards. Thirteen new host records and 2 new locality records are reported.

Twenty-one grass snakes, Natrix natrix, and 24 dice snakes, Natrix tessellata, from Turkey were examined for helminths. Natrix natrix harbored 5 species of Digenea: Astiotrema monticelli, Encyclometra colubrimurorum, Macrodera longicollis, Paralepoderma cloacicola, and Telorchis assula; 2 species of Cestoda: Ophiotaenia europaea and Spirometra erinaceieuropae; and 2 species of Nematoda: Rhabdias fuscovenosa and larvae of Eustrongylides excisus. Natrix tessellata snakes harbored 1 species of Digenea, Telorchis assula; 1 species of Cestoda, Ophiotaenia europaea; and 2 species of Nematoda, Rhabdias fuscovenosa and larvae of Eustrongylides excisus. Turkey is a new locality record for A. monticelli, P. cloacicola, T. assula, O. europaea, S. erinaceieuropae, larvae of E. excisus and R. fuscovenosa.

Microhabitat specificity of Paulisentis missouriensis (Acanthocephala) in the intestine of creek chub (Semotilus atromaculatus) was studied. Data from 64 naturally infected fish harboring only P. missouriensis were utilized to determine if site specificity of worms varied by sex, size, and reproductive maturity, and to test the hypothesis that the first flexure of the intestine of creek chub is the preferred microhabitat, as reported in the literature. Location of worms within the intestine did not differ among size classes of either female or male worms. However, gravid female worms occupied intestinal segments around the first flexure of the intestine, whereas nongravid females were concentrated in the posterior part of the intestine around the second flexure. The distribution of males coincided with that of gravid females. These data suggest that P. missouriensis initially establishes in the posterior regions of the intestine of creek chub, after which they move anteriorly, mate, and come to occupy positions centered around the first flexure of the intestine.

Eleven species of helminths (7 trematodes, 3 cestodes, and 1 acanthocephalan) were recovered from 12 spotted sandpipers, Actitis macularius (Linnaeus, 1766), collected from marine habitats in New Brunswick, Canada, during fall migration in August of 2003. All 12 sandpipers were infected, with the numbers of helminths ranging from 2 to 942 individuals; species richness ranged from 2 to 7. The cestode Anomotaenia hypoleuci was the most prevalent helminth and is designated a host specialist. The trematodes Microphallus papillorobustus and Maritrema subdolum were the most abundant helminths. Adult birds tended to have fewer parasites than juveniles, but the data are inconclusive. Each of the helminth species represents a new host record. A checklist of helminth parasites reported from the spotted sandpiper in North and South America is included.

Nine species of helminths (5 trematodes and 4 cestodes) were recovered from 10 (3 adults, 7 juveniles) ruddy turnstones, Arenaria interpres, collected from a marine habitat on Miscou Island in New Brunswick, Canada, during fall migration in August of 2003. The number of helminths per bird ranged from 24 to 36,217 individuals; the number of helminth species per bird ranged from 3 to 6. The parasite taxa were typically distributed, with 2 or 3 species predominant and the remaining species making up a relatively small proportion of the total. The cestode Anomotaenia clavigera was the most prevalent helminth; the trematodes Microphallus papillorobustus and Maritrema subdolum were the most abundant helminths, together accounting for 94.6% of all helminths recovered. This study is the first to examine the helminth parasites of turnstones during fall migration. A checklist of helminth parasites previously reported from the ruddy turnstone is included.

A survey collection of arthropods associated with bats documents new distributional records of Bolivian ectoparasites. New species records include Acari: Mesostigmata: Spinturnicidae—Periglischrus caligus Kolenati, Periglischrus iheringi Oudemans, Periglischrus ojasti Machado-Allison; Macronyssidae—Radfordiella oudemansi Fonseca; Metastigmata: Argasidae—Ornithodoros hasei (Schulze); Insecta: Diptera: Streblidae—Anastrebla caudiferae Wenzel, Anastrebla modestini Wenzel, Anatrichobius scorzai Wenzel, Exastinion deceptivum Wenzel, Megistopoda theodori Wenzel, Neotrichobius delicatus (Machado-Allison), Paradyschiria fusca Speiser, Paraeuctenodes similis Wenzel, Strebla curvata Wenzel, Strebla guajiro (García & Casal), Trichobius petersoni Wenzel, and Trichobius tiptoni Wenzel.

A new host record is reported for the ixodid tick Bothriocroton hydrosauri from near Burra in South Australia. The tick was recovered from an adult male of the scincid lizard Tiliqua adelaidensis, the pygmy bluetongue lizard. The low prevalence (1 record in >300 lizards examined) suggests this small lizard is not usually infested.

The tapeworm Alcataenia larina (Cestoda: Cyclophyllidea: Dilepididae) is a parasite of gulls (Laridae) with a Holarctic distribution in oceanic and littoral habitats. Two subspecies Alcataenia larina pacifica and Alcataenia larina larina are recognized with the former occurring in the North Pacific basin and the latter in the North Atlantic. Alcids serve as incidental hosts for both species and infections are generally rare, usually involving few specimens. We report A. l. larina in Atlantic puffins (Fratercula arctica) collected from the Bay of Exploits, Newfoundland. The 14 strobilate and early gravid specimens were clearly distinguishable from the closely related Alcataenia cerorhincae and Alcataenia fraterculae by the smaller dimensions of the rostellar hooks and cirrus sac. Increasing numbers of gulls around seabird colonies in Newfoundland may result in more frequent contact between gulls and alcids, such as puffins (during foraging), promoting cross infections of A. l. larina.

The para-receptacle structure (PRS) was first described in Neoechinorhynchus (Neoechinorhynchus) qatarensis Amin, Saoud, and Alkuwari, 2002 (Neoechinorhynchidae), as a prominent vesicle connected proximally to the anterior body wall and distally to the posterior wall of the proboscis receptacle then extending into the body cavity of males and females as a posterior conduit tube. The PRS has since been observed in Neoechinorhynchus (Neoechinorhynchus) golvani Salgado-Maldonado, 1978 (a new subgeneric diagnosis), and described in a member of another eoacanthocephalan family, Acanthogyrus (Acanthosentis) parareceptaclis Amin, 2005 (Quadrigyridae). In the latter species, a similar structure was also observed at the posterior end of the trunk. Our optical and transmission electron microscopy (TEM) observations in specimens of N. qatarensis show the PRS as a tandemly arranged set of nucleated cells delimited by a double-walled membrane and a muscular wall. It appears to be contractile with a secretory function related to changes in the hydrostatic pressure that may be associated with the extrusion and retraction of the proboscis in worms with weakly developed proboscis receptacle musculature. This is the first detailed study of the PRS and of its proposed function in the only 3 acanthocephalan species from which it has been identified to date. It is considered as an archaic structure present only in a few representatives of some primitive taxa having only a single-walled proboscis receptacle wall.

Using energy-dispersive x-ray analysis (EDXA) in conjunction with a scanning electron microscope, high levels of sulfur were recorded in proboscis hooks of 5 species of Acanthocephala: Neoechinorhynchus qatarensis Amin, Saoud, and Alkuwari, 2002; Acanthocephalus dirus (Van cleave, 1931); Neoechinorhynchus idahoensis Amin and Heckmann, 1992, Echinorhynchus salmonis (Müller, 1784); and Pseudoacanthocephalus sp. Petrochenko, 1956. Sulfur was also present in eggs of N. qatarensis. No sulfur was recorded in the body of worms. The 5 species of Acanthocephala were obtained from several fish hosts and 1 toad species from 7 geographical locations. Sulfur ions are probably present in disulphide bonds characteristic of 2 amino acids, cystine and cysteine, which are common amino acids in the protein of mammalian hair and horns and are probably associated with the hardness of acanthocephalan proboscis hooks and egg shells.