Pachysentis Procumbens

''Pachysentis'' is a genus in Acanthocephala (thorny-headed worms, also known as spiny-headed worms) that parasitize primates and carnivorans. They are distributed across Africa, the Middle East, and the Americas. ''Pachysentis'' species attach themselves to the inner lining of the gastrointestinal tract of their hosts using their hook-covered proboscis. Their life cycle includes an egg stage found in host feces, a cystacanth (larval) stage in an intermediate host such as the Egyptian cobra, and an adult stage where cystacanths mature in the intestines of the host. This genus appears identical to the closely related '' Oncicola'' apart from a greater number of hooks on the proboscis. There are eleven species assigned to this genus, although ''P. septemserialis'' is of uncertain taxonomic status. The female worms range from long and wide in ''P. lauroi'' to long and wide in ''P. dollfusi''. Virtually all of the length is the trunk, with a short proboscis. There is pronounced sexual dimorphism in this species as females are around twice the size of the males.

Taxonomy

Phylogenetic analysis has been conducted on one of the eleven species in the genus, ''P. canicola''. Sequences of the molecular marker 18S rDNA
gene were compared to the same sequences in related species and it was concluded that ''P. canicola'' samples formed a well-supported group with other species in the family Oligacanthorhynchidae. Phylogenetic analyses have also been conducted on ''Oncicola'', a genus morphologically nearly identical to ''Pachysentis'' apart from the number of hooks on the proboscis, and have also placed it in the family Oligacanthorhynchidae. The type species for ''Pachysentis'' is ''P. canicola''. In 1972, Schmidt reclassified six species from the ''Prosthenorchis'' genus and one species from the ''Oncicola'' genus into the genus Pachysentis''.

Description

''Pachysentis'' looks identical to the closely related ''Oncicola'' apart from the number of hooks on the proboscis. Species of ''Oncicola'' have 36 or fewer hooks whereas species of ''Pachysentis'' have more. The probosces of ''Pachysentis'' species are not quite spherical and contain 42 to 102 hooks arranged into 12 longitudinal rows of 3 to 12 hooks each. Depending on the species, the rows may be regularly or irregularly alternating and straight or crooked. Hooks have tips with or without barbs, and the larger hooks with complex heads (manubria) and roots with the remaining spines being rootless. The trunk is around twice as long as wide with the anterior half usually wider than the posterior half. The testes are in tandem with at least one located before the middle of the worm. There are eight cement glands compactly arranged each with a single giant nucleus used to temporarily close the posterior end of the female after copulation. The eggs have a sculptured outer membrane. Species can be distinguished based on the number and arrangements of proboscis hooks, whether these hooks are barbed, the arrangement of the cement glands, host, and the length of lemnisci (bundles of sensory nerve fibers).

Species

The genus ''Pachysentis'' Meyer, 1931 contains eleven species, although ''P. septemserialis'' is of uncertain taxonomic status.

*''Pachysentis angolensis'' (Golvan, 1957)

''P. angolensis'' was found infesting the side-striped jackal (''Canis adustus''). The proboscis has a total of 42 hooks without barbs in 12 regularly alternating rows of three and four hooks (six rows of each). The eight cement glands are organized in pairs. This species is named after Angola, the country where it was first discovered.

*''Pachysentis canicola'' Meyer, 1931

''P. canicola'' was found infesting the red fox (''Vulpes vulpes'') in Bushehr, Bushehr Province, Iran, the golden jackal (''Canis aureus'') also in Iran, captive maned wolves (''Chrysocyon brachyurus'') in a zoo in Texas, and the striped skunk (''Mephitis mephitis'') found nearby. It was also found infesting the western diamondback rattlesnake (''Crotalus atrox''). It is the type species of the genus ''Pachysentis''. The species name '' canicola'' is derived from the Latin word for canine which is the type of creature (family Canidae) that this species infests.

*''Pachysentis dollfusi'' (Machado-Filho, 1950)

''P. dollfusi'' was found infesting the intestines of the common brown lemur (''Eulemur fulvus'') in a Brazilian zoo but originally from the island of Madagascar. It is thus unknown if the worm originates from Brazil or Madagascar. The proboscis has 48 barbed hooks arranged into six rows of four hooks each followed by another six rows of four hooks each. The cement glands are in uniform pairs. It is synonymous with ''Prosthenorchis spirula'' Travassos 1917. It is named after the parasitologist Robert-Philippe Dollfus.

*''Pachysentis ehrenbergi'' Meyer, 1931

''P. ehrenbergi'' was found infesting the red fox (''Vulpes vulpes'') in Egypt and in an intermediate host, the Egyptian cobra (''Naja haje''). The proboscis is armed with 102 barbed hooks arranged into six rows of nine each followed by six rows of eight hooks each. ''P. ehrenbergi'' was reported infesting the body cavity of 5.4% of a sample of African five-lined skinks (''Trachylepis quinquetaeniata'') in the Qena Governorate of Egypt, however the measurements and morphological description do not match either the original description by Meyer in 1931 or the reexamination of original specimens by Gomes and colleagues in 2019. Juvenile ''P. ehrenbergi'' have been reported infesting the long-eared hedgehog (''Hemiechinus auritus'') in the Faran Oasis, South Sinai, Egypt. Juvenile trunk length is reported to be 3.22–4.16 mm by 0.87–1.04 mm, the proboscis length to be 0.42–0.60 mm in length by 0.45–0.68 mm in width, the proboscis sheath to be 0.79–1.0 mm by 0.37–0.52 mm (whereas the measurements given by Meyer in the original 1931 description is larger, at 1.3 mm in length and the proboscis measuring 0.8 mm in length by 0.9 mm in width). The anterior proboscis hooks in the juveniles are reported to be large, from 0.078–0.086 mm long, and the posterior hooks smaller, from 0.052–0.062 mm.

*''Pachysentis gethi'' (Machado-Filho, 1950)

''P. gethi'' was originally described in 1950 by Machado-Filho infesting tayra (''Eira barbara'') in Pará and Rio de Janeiro, Brazil but this remained the only record until it was rediscovered in 2016 infesting the wild lesser grison (''Galictis cuja''), also in Rio de Janeiro, with different measurements. The proboscis has 42 hooks without barbs arranged into six rows of four hooks followed by six rows of three hooks. The eight cement glands occur in pairs. The species is named after Dr. Geth Jansen.

*''Pachysentis lauroi'' Gomes, Amin, Olifiers, Bianchi, Souza, Barbosa & Maldonado, 2019

''P. lauroi'' has been found infesting the South American coati (''Nasua nasua'') in Mato Grosso do Sul, Brazil. The proboscis has 48 barbed hooks arranged into six rows of four hooks followed by six rows of four hooks. The eight cement glands are clustered. It was found in the small intestine. The species is named after , a parasitologist who studied Brazilian Acanthocephala.

*''Pachysentis lenti'' (Machado-Filho, 1950)

''P. lenti'' has been found infesting the white-headed marmoset (''Callithrix geoffroyi'') in Espírito Santo, Brazil. The proboscis has 48 hooks without barbs arranged into six rows of four hooks followed by six rows of four hooks. It is named after , a Brazilian parasitologist.

*''Pachysentis procumbens'' Meyer, 1931

''P. procumbens'' has been found infesting the red fox (''Vulpes vulpes'') in Argo, Egypt. The proboscis has 90 hooks without barbs arranged into six rows of seven hooks followed by six rows of eight hooks. The species name is from the Latin ''procumbent'', meaning "lying prostrate".

*''Pachysentis procyonis'' (Machado-Filho, 1950)

''P. procyonis'' was found infesting the intestines of a crab-eating raccoon (''Procyon cancrivorus'') in Rio de Janeiro, Brazil. The proboscis has 42 hooks without barbs arranged into six rows of four hooks followed by six rows of three hooks. Distinguishing features include eight clustered cement glands and very short lemnisci that do not reach the anterior testis. The species is named after the genus of the host (''Procyon'') it was found infesting. It is the only known parasite of the crab-eating racoon in Brazil.

*''Pachysentis rugosus'' (Machado-Filho, 1950)

''P. rugosus'' has been found to infest the large intestine of Azaras's capuchin (''Sapajus cay'') in Rio de Janeiro, Brazil, and the tufted capuchin (''Sapajus apella''), also in Brazil. The proboscis is armed with 42 hooks without barbs arranged into six rows of four hooks each followed by six rows of three hooks each. This species can be identified by its clustered cement glands and long leminisci that reach the anterior testis. The species name ''rugosus'' is Latin for 'wrinkled'.

*''Pachysentis septemserialis'' (Machado-Filho, 1950)

''P. septemserialis'' is considered by Gomes ''et al.'' in 2019 to have an uncertain taxonomic status due to differences between the paratypes morphological characteristics and the original description, the similarity in hosts (primates of the family Callitrichidae including the black tamarin (''Saguinus niger''), and the absence of samples or measurements of adult males. Morphologically, new observations by Gomes ''et al.'' in 2019 suggest it is synonymous with ''P. lenti''. Specifically, the original description of one paratype described the lack of a collar at the base of the proboscis whereas a collar was observed in the paratype by Gomes ''et al.'' in 2019 (suggesting affiliation with the genus '' Prosthenorchis''). A second discrepancy from another paratype is the number of hooks; 12 longitudinal rows of four hooks with total of 48 hooks were observed by Gomes ''et al.'' in 2019 but contradicts the seven rows of seven hooks with a total of 49 hooks given in the original description by Machado-Filho in 1950. The name ''septemserialis'' refers to the seven rows in series.

Distribution

The distribution of ''Pachysentis'' species is determined by that of its hosts. ''Pachysentis'' species have been found in South America (Brazil), Africa (Egypt and Angola), Asia (Egypt and Iran).

Hosts

The life cycle of an acanthocephalan consists of three stages beginning when an infective acanthor (development of an egg) is released from the intestines of the definitive host and then ingested by an arthropod, the intermediate host. The intermediate hosts of most ''Pachysentis'' species are not known. When the acanthor molts, the second stage called the acanthella begins. This stage involves penetrating the wall of the mesenteron or the intestine of the intermediate host and growing. The final stage is the infective cystacanth which is the larval or juvenile state of an Acanthocephalan, differing from the adult only in size and stage of sexual development. The cystacanths within the intermediate hosts are consumed by the definitive host, usually attaching to the walls of the intestines, and as adults they reproduce sexually in the intestines. The acanthor is passed in the feces of the definitive host and the cycle repeats.

''Pachysentis'' species exclusively parasitize primates and carnivorans as their primary host. Paratenic hosts (hosts where parasites infest but do not undergo larval development or sexual reproduction) for ''Pachysentis'' have been found for ''P. ehrenbergi'' (Egyptian cobra, ''Naja haje'') and ''P. canicola'' (western diamondback rattlesnake, ''Crotalus atrox''). There are no reported cases of any ''Pachysentis'' species infesting humans in the English language medical literature.

File:Side-striped Jackal (Canis adustus)- rare sighting of this nocturnal animal ... (13799300905).jpg, alt=A side-striped jackal walking in front of grass, The side-striped jackal is one of the hosts of ''P. angolensis''
File:Fox - British Wildlife Centre (17429406401).jpg, alt=A red fox walking on grass, The red fox is one of the hosts of ''P. canicola'' and ''P. procumbens''
File:Common brown lemur (Eulemur fulvus) male.jpg, alt=A Common brown lemur on the side of a tree branch, The common brown lemur is one of the hosts of ''P. dollfusi''
File:Tayra - Male, Brazil.jpg, alt=A Tayra on a grassy field, The tayra is one of the hosts of ''P. gethi''
File:Nasenbaer Nasua nasua Zoo Augsburg-04.jpg, alt=A South American coati on a branch in a forest, The South American coati is one of the hosts of ''P. louroi''
File:Geoffroy's Marmoset 1.jpg, alt=A White-headed marmoset on a tree, The white-headed marmoset is one of the hosts of ''P. lenti ''
File:CostaRica ManuelAntonioNationalPark Racoon (pixinn.net).jpg, alt=A crab-eating racoon eating a fruit on a beach, The crab-eating raccoon is one of the hosts of ''P. procyonis''
File:Sapajus libidinosus paraguayanus.jpg, alt=Azaras's capuchin on a branch in a forest, The Azaras's capuchin is one of the hosts of ''P. rugosus''
File:Crotalus atrox USFWS.jpg, alt=Western diamondback rattlesnake in grass in a threatening pose, The western diamondback rattlesnake is a paratenic host of ''P. canicola''
File:Naja haje (1).jpg, alt=Head of the Egyptian cobra, The Egyptian cobra is a paratenic host of ''P. ehrenbergi''

Notes

References

{{Taxonbar, from=Q3825715

Archiacanthocephala
Acanthocephala genera