Pachysentis
Proboscis of P. lenti[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Acanthocephala
Class:	Archiacanthocephala
Order:	Oligacanthorhynchida
Family:	Oligacanthorhynchidae
Genus:	Pachysentis Meyer, 1931[2]
Type species
Pachysentis canicola Meyer, 1931
Other species
Pachysentis angolensis Pachysentis dollfusi Pachysentis ehrenbergi Pachysentis gethi Pachysentis lauroi Pachysentis lenti Pachysentis procumbens Pachysentis procyonis Pachysentis rugosus Pachysentis septemserialis?

Pachysentis is a genus in Acanthocephala (thorny-headed worms, also known as spiny-headed worms) that parasitize primates and carnivorans by attaching themselves to the intestines 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 has an uncertain taxonomic status. The female worms range from 12 millimetres (0.47 in) long and 1.6 millimetres (0.063 in) wide in P. lauroi to 50 millimetres (2.0 in) long and 4 millimetres (0.16 in) wide in P. dollfusi. Virtually all of the length is the trunk with a short proboscis covered in hooks used to attach to the inner lining of the gastrointestinal tract of their hosts. There is pronounced sexual dimorphism in this species as females are around twice the size of the males. Pachysentis species are distributed across Africa, the Middle East, and the Americas.

Taxonomy

Phylogenetic analysis has been conducted on one of the eleven species in the genus, P. canicola, and confirms that this species forms an independent group in the family Oligacanthorhynchidae.^[3] 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 placed it in the family Oligacanthorhynchidae.^[4] The type species for Pachysentis is P. canicola.^[5][1] In 1972, Schmidt reclassified six species from the Prosthenorchis genus and one species from the Oncicola genus into the genus Pachysentis.^[6]

Description

Pachysentis look 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 contains 42 to 102 hooks arranged into 12 longitudinal rows of 3 to 12 hooks each. 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 fairly wide relative to the length 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.^[8][9] 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.^[1]

Species

The genus Pachysentis Meyer, 1931 contains eleven species although P. septemserialis has an uncertain taxonomic status.^{[1][10][lower-alpha 4]}

• Pachysentis angolensis (Golvan, 1957)^{[11][lower-alpha 5]}

P. angolensis was found infesting the side-striped jackal (Canis adustus). This species is named after Angola, the country where it was first discovered. The proboscis has a total of 42 hooks without barbs in 12 regularly alternating rows of three and four hooks (six rows of each).^[11] The eight cement glands are organized in pairs.^[1]

• Pachysentis canicola Meyer, 1931^[2]

P. canicola was found infesting the red fox (Vulpes vulpes) in Bushehr, Bushehr Province, Iran,^[12] the golden jackal (Canis aureus) also in Iran,^[13] the maned wolf (Chrysocyon brachyurus) in Texas, and the striped skunk (Mephitis mephitis), also in Texas.^[3] It was also found infesting the western diamondback rattlesnake (Crotalus atrox).^[14][15] It is the type species of the genus Pachysentis.^[2] The species name canicola is derived from the Latin word for canine which is the type of creature (family Canidae) that this species infests.^[2]

• Pachysentis dollfusi (Machado-Filho, 1950)^{[16][lower-alpha 6]}

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.^[16] It is thus unknown if the worm originates from Brazil or Madagascar.^[1] The proboscis has 48 barbed hooks arranged into six rows of four hooks each followed by six rows of four hooks each. The cement glands are in uniform pairs.^[1] It is synonymous with Prosthenorchis spirula Travassos 1917.^[17] It is named after the parasitologist Robert-Philippe Dollfus.^[16]

• Pachysentis ehrenbergi Meyer, 1931^[2]

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.^[1] 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^[2] or the reexamination of original specimens by Gomes et al. in 2019.^[1] 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.^[18]

• Pachysentis gethi (Machado-Filho, 1950)^{[16][lower-alpha 7]}

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.^[19] 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.^[1] The species is named after Dr. Geth Jansen.^[16]

• Pachysentis lauroi Gomes, Amin, Olifiers, Bianchi, Souza, Barbosa & Maldonado, 2019^[1]

Diagram of a male P. lauroi showing the anterior and posterior testes, and eight cements glands in a clustered arrangement.^[1]

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.^[1] The species is named after Lauro Travassos, a parasitologist who studied Brazilian Acanthocephala.^[1]

• Pachysentis lenti (Machado-Filho, 1950)^{[16][lower-alpha 8]}

P. lenti has been found infesting the white-headed marmoset (Callithrix geoffroyi) in Espirito Santo, Brazil. The proboscis has 48 hooks without barbs arranged into six rows of four hooks followed by six rows of four hooks.^[1] It is named after Herman Lent, a Brazilian parasitologist.^[16]

• Pachysentis procumbens Meyer, 1931^[2]

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. ^[1] The species name is a form of the Latin for "procumbent", meaning "lying prostrate".^[20]

• Pachysentis procyonis (Machado-Filho, 1950)^{[16][lower-alpha 9]}

P. procyonis was found infesting the intestines of a crab-eating raccoon (Procyon cancrivorus) in Rio de Janeiro, Brazil.^[21] 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.^[1] The species is named after the genus of the host (Procyon) it was found infesting.^[16] It is the only known parasite of the crab-eating racoon in Brazil.^[22]

• Pachysentis rugosus (Machado-Filho, 1950)^{[16][lower-alpha 10]}

P. rugosus have been found infesting the large intestines of Azaras's capuchin (Sapajus cay) in Rio de Janeiro, Brazil, and the tufted capuchin (Sapajus apella), also in Brazil.^[23] 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 their clustered cement glands and long leminisci that reach the anterior testis. ^[1] The species name rugosus is Latin for 'wrinkled'.

• Pachysentis septemserialis (Machado-Filho, 1950)^{[16][lower-alpha 11]}

P. septemserialis is considered to have uncertain taxonomic status by Gomes (2019) due to the differences between the paratypes morphological characteristics and those of the original description, the similarity in hosts (primates of the family Callitrichidae including the black tamarin (Saguinus niger),^[24] and the absence of samples or measurements of adult males. Specifically, the original description of one paratype described the lack of a collar at the base of the proboscis whereas a collar was observed (suggesting affiliation with the genus Prosthenorchis). A second discrepancy from another paratype is the incorrect number of hooks; 12 longitudinal rows of four hooks with total of 48 hooks were observed but contradicts the seven rows of seven hooks with a total of 49 hooks given in the original description. The name septemserialis refers to the seven rows in series.^[16] Morphologically, new observations suggests it is synonymous with P. lenti.^[1]

Distribution

P. angolensis

P. canicola

P. canicola

P. dollfusi?

P. dollfusi?

P. ehrenbergi

P. gethi

P. gethi, P. procyonis, P. rugosus

P. lauroi

P. lenti

P. procumbens

Worldwide distribution of Pachysentis samples collected in the field. It is thus unknown if P. dollfusi originates from Brazil or Madagascar as it was discovered in a Brazilian zoo in a lemur from Madagascar.^[1]

The distribution of Pachysentis species is determined by that of its hosts. Pachysentis species have been found in North America (Texas), South America (Brazil), Africa (Egypt and Angola), Asia (Egypt and Iran).^[1]

Hosts

Life cycle of Acanthocephala.^{[25][lower-alpha 12]}

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 are passed in the feces of the definitive host and the cycle repeats.^[27]

Pachysentis species exclusively parasitize primates and carnivorous mammals as their primary host.^[1] Paratenic hosts (hosts where parasites infest but do not undergo larval development or sexual reproduction) for Pachysentishave been found for P. ehrenbergi (Egyptian cobra, Naja haje)^[18] and P. canicola (western diamondback rattlesnake, Crotalus atrox).^[15] Pachysentis species are distributed in Africa and North, Central and South America.^[1] There are no reported cases of any Pachysentis species infesting humans in the English language medical literature.^[26]

• Hosts for Pachysentis species
• 
  The side-striped jackal is one of the hosts of P. angolensis
• 
  The red fox is one of the hosts of P. canicola and P. procumbens
• 
  The common brown lemur is one of the hosts of P. dollfusi
• 
  The tayra is one of the hosts of P. gethi
• 
  The South American coati is one of the hosts of P. louroi
• 
  The white-headed marmoset is one of the hosts of P. lenti
• 
  The crab-eating raccoon is one of the hosts of P. procyonis
• 
  The Azaras's capuchin is one of the hosts of P. rugosus
• 
  The western diamondback rattlesnake is a paratenic host of P. canicola
• 
  The Egyptian cobra is a paratenic host of P. ehrenbergi

Notes

References