Pachysentis is a genus of Acanthocephala (thorny-headed worms, also known as spiny-headed worms) that parasitize carnivourous mammals 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. Pachysentis species are distributed across Africa and the Americas.
Phylogenetic analysis has been conducted on one of the eleven species in the genus, P. canicola, using the gene for 18S ribosomal RNA and ITS1-5.8-ITS2 region of ribosomal RNA, 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][2]
Archiacanthocephala Archiacanthocephala Oligacanthorhynchidae Moniliformidae Gigantorhynchida Phylogenetic reconstruction for select species in the class Archiacanthocephala[4][6][3]Pachysentis look identical to the closely related Oncicola apart from the number of hooks on the proboscis. Species of Oncicola have 36 or less 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.[7][8] 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.[2]
The genus Pachysentis Meyer, 1931 contains eleven species although P. septemserialis has an uncertain taxonomic status.[2][9][d]
P. angolensis was found infesting the side-striped jackal (Canis adustus). This species is named after Angola, the site 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).[10] The eight cement glands are organized in pairs.[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.[1] The species name canicola is derived from the Latin word for canine which is the type of creature (family Canidae) that this species infests.[1]
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.[2] 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.[2] It is synonymous with Prosthenorchis spirula Travassos 1917.[17] It is named after the parasitologist Robert-Philippe Dollfus.[16]
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 hooks each followed by six rows of eight hooks each.[2] 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[1] or the reexamination of original specimens by Gomes et al. in 2019.[2] 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]
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.[2] The species is named after Dr. Geth Jansen.[16]
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.[2] The species is named after Lauro Travassos, a parasitologist who studied Brazilian Acanthocephala.[2]
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.[2] It is named after Herman Lent, a Brazilian parasitologist.[16]
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. [2] The species name is a form of the Latin for "procumbent", meaning "lying prostrate".[20]
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.[2] 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]
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. [2] The species name rugosus is Latin for wrinkled.
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.[2]
Pachysentis species exclusively parasitize carnivourous mammals as their primary host. Reptilian intermediate hosts have been found for P. ehrenbergi and P. canicola.
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The Side-striped jackal is one of the hosts of P. angolensis
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The red fox is one of the hosts of P. canicola and P. procumbens
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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
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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 an intermediate hosts of P. canicola
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The Egyptian cobra is an intermediate hosts of P. ehrenbergi
Pachysentis is a genus of Acanthocephala (thorny-headed worms, also known as spiny-headed worms) that parasitize carnivourous mammals 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. Pachysentis species are distributed across Africa and the Americas.
