The Pentastomida are an enigmatic group of
parasitic
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
arthropods
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
commonly known as tongue worms due to the resemblance of the species of the genus ''Linguatula'' to a vertebrate
tongue
The tongue is a muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper surfa ...
; molecular studies point to them being degenerate
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s.
About 130 species of pentastomids are known; all are
obligate parasite
An obligate parasite or holoparasite is a parasitic organism that cannot complete its life-cycle without exploiting a suitable host. If an obligate parasite cannot obtain a host it will fail to reproduce. This is opposed to a facultative parasite, ...
s with correspondingly degenerate anatomy. Adult tongue worms vary from about in length, and parasitise the
respiratory tract
The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.
Air is breathed in through the nose to th ...
s of
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s. They have five anterior
appendage
An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body.
In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...
s. One is the mouth; the others are two pairs of hooks, which they use to attach to the host. This arrangement led to their scientific name, meaning "five openings", but although the appendages are similar in some species, only one is a mouth.
Taxonomy
Historically significant accounts of tongue worm biology and systematics include early work by
Josef Aloys Frölich,
Alexander von Humboldt
Friedrich Wilhelm Heinrich Alexander von Humboldt (14 September 17696 May 1859) was a German polymath, geographer, naturalist, explorer, and proponent of Romantic philosophy and science. He was the younger brother of the Prussian minister, p ...
,
Karl Asmund Rudolphi
Karl Asmund Rudolphi (14 July 1771 – 29 November 1832) was a Swedish-born German natural history, naturalist, who is credited with being the "father of helminthology".
Life
Rudolphi was born in Stockholm to German parents. He was awarded hi ...
,
Karl Moriz Diesing
Karl (Carl) Moriz (Moritz) Diesing (16 June 1800, in Krakow – 10 January 1867, in Vienna) was an Austrian naturalist and zoologist, specializing in the study of helminthology.
He studied medicine at the University of Vienna, earning his doctor ...
and
Rudolph Leuckart
Karl Georg Friedrich Rudolf Leuckart (7 October 1822 – 22 February 1898) was a German zoologist born in Helmstedt. He was a nephew to naturalist Friedrich Sigismund Leuckart (1794–1843).
Academic career
He earned his degree from the Uni ...
.
Other important summaries have been published by
Louis Westenra Sambon
Louis Westenra Sambon (original first name Luigi, 7 November 1867 – 30 August 1931) was an Italian-English physician who played important roles in understanding the causes ( etiology) of diseases. He described many pathogenic protozoans, insect ...
,
Richard Heymons and John Riley, and a review of their evolutionary relationships with a bibliography up to 1969 was published by J. T. Self.
Affinities
The affinities of tongue worms have long proved controversial. Historically, they were initially compared to various groups of parasitic worms. Once the arthropod-like nature of their cuticle was recognised, similarities were drawn with mites, particularly gall mites (
Eriophyidae
Eriophyidae is a family of more than 200 genera of mites, which live as plant parasites, commonly causing galls or other damage to the plant tissues and hence known as gall mites. About 3,600 species have been described, but this is probably l ...
). Although gall mites are much smaller than tongue worms, they also have a long, segmented body and only two pairs of legs. Later work drew comparisons with millipedes and centipedes (
Myriapoda
Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial.
The fossil record of myriapods reaches back into the late Silurian, a ...
), with velvet worms (
Onychophora
Onychophora (from grc, ονυχής, , "claws"; and , , "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus ...
) and water bears (
Tardigrada
Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbä ...
). Some authors interpreted tongue worms as essentially intermediate between
annelids
The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecolo ...
and
arthropods
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
, while others suggested that they deserved a
phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...
of their own. Tongue worms grow by
moulting
In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
, which suggests they belong to
Ecdysozoa
Ecdysozoa () is a group of protostome animals, including Arthropoda (insects, chelicerata, crustaceans, and myriapods), Nematoda, and several smaller phyla. They were first defined by Aguinaldo ''et al.'' in 1997, based mainly on phylogenetic tr ...
, while other work has identified the arthropod-like nature of their larvae. In general, the two current alternative interpretations are: pentastomids are highly modified and parasitic crustaceans, probably related to fish lice, or they are an ancient group of stem-arthropods, close to the origins of Arthropoda.
Crustaceans
The discovery that tongue worms are
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s can be traced back to the work of
Pierre-Joseph Van Beneden
Pierre-Joseph van Beneden FRS FRSE FGS FZS (19 December 1809 – 8 January 1894) was a Belgian zoologist and paleontologist.
Life
Born in Mechelen, Belgium, he studied medicine at the State University of Leuven, and studied zoology in Paris unde ...
, who compared them to parasitic
copepod
Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...
s. The modern form of this hypothesis dates from Karl Georg Wingstrand's study of
sperm
Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...
morphology, which recognised similarities in sperm structure between tongue worms and fish lice (
Argulidae
The family Argulidae, whose members are commonly known as carp lice or fish lice, are parasitic crustaceans in the class Ichthyostraca. It is the only family in the monotypic subclass Branchiura and the order Arguloida, although a second family, ...
) – a group of
maxillopod crustaceans which live as parasites on fish and occasionally amphibians. John Riley and colleagues also offered a detailed justification for the inclusion of the tongue worms among the crustaceans. The fish louse model received significant further support from the molecular work of Lawrence G. Abele and colleagues. A number of subsequent molecular phylogenies have corroborated these results,
and the name Ichthyostraca has been proposed for a (Pentastomida + Branchiura) clade. Thus a number of important standard works and databases on crustaceans now include the pentastomids as members of this group.
Stem-arthropods
Critics of the Ichthyostraca classification have pointed out that even parasitic crustaceans can still be recognised as crustaceans based on their larvae; but that tongue worms and their larvae do not express typical characters for Crustacea or even
Euarthropoda
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, oft ...
. An alternative model notes the extremely ancient Cambrian origins of these animals and interprets tongue worms as stem-group arthropods. A recent morphological analysis recovered Pentastomida outside the arthropods, as sister group to a clade including
nematode
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...
s,
priapulids
Priapulida (priapulid worms, from Gr. πριάπος, ''priāpos'' ' Priapus' + Lat. ''-ul-'', diminutive), sometimes referred to as penis worms, is a phylum of unsegmented marine worms. The name of the phylum relates to the Greek god of fertili ...
and similar ecdysozoan 'worm' groups. Adding fossils, they suggested an extinct animal called ''
Facivermis
''Facivermis'' (meaning "torch worm" ) is a genus of sessile lobopodian from the Lower Cambrian Maotianshan shales of China
Anatomy
''Facivermis'' was a worm-like creature up to 90 mm long. Its body was divided into three sections. The ante ...
'' could be closely related to tongue worms. However it should be stressed that these authors did not explicitly test pentastomid/crustacean relationships.
Fossil record
Exceptionally preserved, three-dimensional and
phosphatised fossils from the Upper
Cambrian
The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...
Orsten
The Orsten fauna are fossilized organisms preserved in the Orsten lagerstätten of Cambrian (Late Miaolingian to Furongian) rocks, notably at Kinnekulle and on the island of Öland, all in Sweden.
The initial site, discovered in 1975 by Klaus Mül ...
of Sweden and the Cambrian/
Ordovician
The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...
boundary of Canada
have been identified as pentastomids. Also one from the Wuluian (middle Cambrian) of Greenland. Four fossil genera have been identified from the Cambrian so far: ''Aengapentastomum'', ''Bockelericambria'', ''Haffnericambria'' and ''Heymonsicambria''. These fossils suggest that pentastomids evolved very early and raise questions about whether these animals were parasites at this time, and if so, on which hosts.
Conodont
Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which ...
s (primitive fish) have sometimes been mentioned as possible hosts in this context.
A fifth genus, ''
Invavita
''Invavita piratica'' is an extinct, parasitic species of tongue worm, provisionally assigned to the order Cephalobaenida, from Herefordshire Lagerstätte, Ludlow-aged England. It possessed a head, a worm-like body, and two pairs of limbs.
...
'', is from
Silurian
The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...
-aged marine strata of England: fossil specimens of ''Invavita'' are found firmly attached to their
ostracod
Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...
hosts of the species ''Nymphatelina gravida''.
It possessed a head, a worm-like body, and two pairs of limbs.
Classification
There are four extant orders recognised in the subclass Pentastomida:
*
Cephalobaenida
*
Porocephalida
Porocephalida is an Order (biology), order of tongue worms. Some species in this order, such as ''Armillifer grandis'', have been found in vipers, with some found in vipers from Bushmeat, bushmeat markets.
Superfamilies and families
There are ...
*
Raillietiellida
*
Reighardiida
Description
Pentastomids are worm-like animals ranging from in length. The female is larger than the male. The anterior end of the body bears five protuberances, four of which are clawed legs, while the fifth bears the mouth. The body is segmented and covered in a
chitin
Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
ous cuticle. The digestive tract is simple and tubular since the animal feeds entirely on blood, except from genus
Linguatula
''Linguatula'' is a genus of crustaceans belonging to the family Linguatulidae. The genus has a cosmopolitan distribution.
Species
There are four species recognised in the genus ''Linguatula'':
*''Linguatula arctica''
*''Linguatula multiannulat ...
which lives in the nasal cavity of carnivorous mammals where they feed mainly on mucus and dead cells, although the mouth is somewhat modified as a muscular pump.
The nervous system is similar to that of other arthropods, including a ventral nerve cord with
ganglia
A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympatheti ...
in each segment. Although the body contains a
haemocoel
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
, no circulatory, respiratory, or excretory organs are present.
[
]
Behaviour and ecology
Pentastomids live in the upper respiratory tract of reptiles, birds, and mammals, where they lay eggs. They are gonochoric
In biology, gonochorism is a sexual system where there are only two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric.
Gonochorism c ...
(having two sexes), and employ internal fertilisation
Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction. For inter ...
. The eggs are either coughed out by the host or leave the host body through the digestive system. The eggs are then ingested by an intermediate host, which is commonly either a fish or a small herbivorous mammal.[
The larva hatches in the intermediate host and breaks through the wall of the intestine. It then forms a cyst in the intermediate host's body. The larva is initially rounded in form, with four or six short legs, but moults several times to achieve the adult form. At least one species, Subtriquetra subtriquetra, has a free living larva. There is both indirect development with nymphal stages and direct development. The pentastomid reaches the main host when the intermediate host is eaten by the main host, and crawls into the respiratory tract from the ]oesophagus
The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
.[
]
Human infestation
Tongue worms occasionally parasitise humans. While a report exists of ''Sebekia'' inducing dermatitis
Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can v ...
,[Correct spelling: Sebakia --> Sebekia, See ] the two genera responsible for most internal human infestation are ''Linguatula
''Linguatula'' is a genus of crustaceans belonging to the family Linguatulidae. The genus has a cosmopolitan distribution.
Species
There are four species recognised in the genus ''Linguatula'':
*''Linguatula arctica''
*''Linguatula multiannulat ...
'' and '' Armillifer''. Visceral pentastomiasis can be caused by ''Linguatula serrata
''Linguatula serrata'' is a species of cosmopolitan zoonotic parasite, belonging to the tongueworm order Pentastomida. They are wormlike parasites of the respiratory systems of vertebrates. They live in the nasopharyngeal region of mammals. Cat ...
'', '' Armillifer armillatus'', ''Armillifer moniliformis'', ''Armillifer grandis
''Armillifer grandis'' is a species of tongue worm in the subclass Pentastomida found in tropical Central and West Africa. Its typical definitive hosts are viperid snakes (such as ''Bitis gabonica, Bitis nasicornis'', and ''Cerastes cerastes ...
'', and '' Porocephalus crotali''.
The terms associated with infections can vary:
* ''Linguatula
''Linguatula'' is a genus of crustaceans belonging to the family Linguatulidae. The genus has a cosmopolitan distribution.
Species
There are four species recognised in the genus ''Linguatula'':
*''Linguatula arctica''
*''Linguatula multiannulat ...
'' disease can be called linguatuliasis or linguatulosis
Linguatulosis is a condition associated with the organism ''Linguatula serrata''.
The usual final host for ''Linguatula serrata'' is a carnivore, like a dog or jackal, and the species is sometimes known as the dog tongueworm for this reason.
More ...
.
* ''Porocephalus'' disease can be called porocephaliasis
Porocephaliasis is a condition associated with species in the closely related genera '' Porocephalus'' and '' Armillifer''. (The term "pentastomiasis" encompasses all diseases of Pentastomida, which includes porocephaliasis and linguatulosis.)
Po ...
or porocephalosis.
* '' Armillifer'' disease can also be called porocephalosis. (An alternate name for ''Armillifer moniliformis'' is ''Porocephalus moniliformis''.)
* "Pentastomiasis" can refer to any infection of Pentastomida.
''Porocephalus'' and ''Armillifer'' (which are all cylindrical and all inhabit snake
Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...
s) have much more in common with each other than they do with ''Linguatula'' (which is flat and inhabits dog
The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...
s and wolves
The wolf (''Canis lupus''; plural, : wolves), also known as the gray wolf or grey wolf, is a large Canis, canine native to Eurasia and North America. More than thirty subspecies of Canis lupus, subspecies of ''Canis lupus'' have been reco ...
).
References
External links
*
{{Taxonbar, from=Q222975
Arthropod subclasses
Parasitic crustaceans
Articles containing video clips
Extant Cambrian first appearances