Tongue worms

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Tongue worms
Males (left) and females (right) of Armillifer sp.

Males (left) and females (right) of Armillifer sp.

Systematics
without rank: Primordial mouths (protostomia)
Over trunk : Molting animals (Ecdysozoa)
Trunk : Arthropod (arthropoda)
Sub-stem : Crustaceans (Crustacea)
Class : Maxillopoda
Subclass : Tongue worms
Scientific name
Pentastomida
Diesing , 1836

The tongue worms (Pentastomida) are a group of parasitic arthropods with around 130 species. Their size varies between a few millimeters and 14 cm in length. As an obligatory parasite of the respiratory organs, they attack carnivorous reptiles , birds and mammals . For some species, humans can also serve as the host of larvae or adult animals. Because of their location, the animals were also called lungworms in the past , and linguatulida (lat. Lingua : tongue) because of their shape .

morphology

Tongue worms are soft-skinned, worm-like animals with a round or flattened body. Externally, the body is usually divided into conspicuous rings, these do not correspond to segments, but are folds of skin. In the genus Armillifer (shown) , the ringlets are arranged in a spiral and give the animal a corkscrew-like appearance. At the front end next to the mouth opening (sometimes on a trunk-shaped projection) sit two pairs of hook-shaped appendages (reshaped extremities) with which the animal anchors itself in the host. The five projections were the basis for the scientific name (Greek: pente, penta-: five and stoma: mouth). The hooks sit behind or next to each other, depending on the family.

As an obligatory parasite, tongue worms have a simplified physique without heart and blood vessels, internal excretory organs or respiratory organs. The body is crossed by a simple, tubular intestine. Otherwise, the body is mostly filled with the large gonads, which in females can contain half a million eggs. Tongue worms are separate sexes, with the male being considerably smaller than the female. Fertilization takes place in the host, then the male dies.

Life cycle

Tongue worms are parasites that develop indirectly. The sexually mature female secretes eggs in the definitive host, which are ingested by an intermediate host with the food. All stages of development up to the 1st larval stage take place in the uterus. Even the primary larva represents the infectious stage for the intermediate host. The larvae hatch in the intestine of the intermediate host, pierce the intestinal wall and live in the body cavity or various organs. The newly hatched larvae already have all segments. After several moults, they encapsulate and develop into the last larval stage, which is infectious for the ultimate host. The number of nymph stages can vary between species. In principle, tongue worms need 4 moults in vertebrates as intermediate hosts, a few of the order Porocephalida require 6–8 moults.

If the intermediate host is eaten by a predator (final host), the larvae migrate into the lungs, where they anchor themselves with their head spikes in the tissue and suck blood. Here they mature to reproduce, which can require several moults. The lifespan of adult worms can be several months. The worms escape the host body's immune defense presumably through a deposited lipid shell that completely covers the actual chitinous body wall, a common defense strategy found in numerous endoparasites.

Modifications to this normal life cycle occur. For example, the species of the genus Linguatula do not live in the lungs, but in the host's nasal cavity, where they feed on mucus and body cells. In a few species, direct development occurs without an intermediate host. These would include the "nose worm" Linguatula arctica the rentiers or Reighardia sternae in seabirds. In at least one species ( Subtriquetra subtriquetra. Porocephalidae) the first larval stage is free-living.

Occurrence

Tongue worms are mainly found in the tropics. Due to the life cycle, the final hosts are predominantly predators (carnivores), over 90% reptiles such as snakes or crocodiles , whereby a single crocodile species of seven or eight species can be infested. Mammals (e.g. big cats like leopards and lions) or birds are less common as hosts. Intermediate hosts can be a large number of amphibian, reptile, mammalian or fish species, and in exceptional cases also insect species.

Systematics

External system

The position of tongue worms in the system has long been controversial. Classification as a separate animal strain with (unclear) relationships to the arthropods was widespread. According to current knowledge, they seem to belong to the crustaceans (Crustacea). This systematic classification is supported by molecular biological studies, but was originally established primarily on the basis of the fine structure of the sperm , which show striking similarities with those of the carp lice (Branchiura), which are accordingly regarded as the sister group of tongue worms. Morphological arguments are now being put forward for this.

Alternatively, a group of taxonomists continues to place them in the stem line of the arthropods as Panarthropoda, together with the columbus and the tardigrade . Important arguments are, in addition to the high age of the group (older than all current host species!), Which is proven by the fossil record, that no morphological apomorphies at all can be given, while these also exist in other parasitic crustaceans with strongly modified morphology (e.g. barnacles ), have always been preserved, at least in the larval stages.

Internal system

Fossil lore

Finding fossils of soft-skinned animals such as tongue worms at all seems hopeless at first glance. Nevertheless, numerous, almost indubitably related forms have now been found from this group. These belong to the Middle and Upper Cambrian , so they are around 500 million years old. They have been preserved thanks to special embedding conditions in which the entire body shell (made of proteins and chitin) was quickly displaced by calcium phosphate after death. The phosphated, only millimeter-sized fossils were then embedded in a limestone, from which they can be exposed by dissolving them with hydrochloric acid. These fossils (called "Orsten" -type from a Swedish expression) are physically preserved; H. not just as a print. The fossil pentastomids, which can be interpreted as benthic larvae, are very similar to today's forms, the most striking difference being that there are two rudimentary legs on the body (today only detectable in the embryo).

In 2015, following the findings of larvae to date, a fossil was first found that was interpreted as an imaginal tongue worm. The species called Invavita piratica comes from the Silurian region of Herefordshire and is around 425 million years old. The millimeter-sized fossils sit as ectoparasites on a species of ostracode . So, unlike today's tongue worms, they were obviously ectoparasites, not endoparasites, and they did not parasitize on vertebrates. According to the new findings, it is considered possible that the parasites were transferred to vertebrates through ingestion, together with the host, through a predatory species, with the subsequent transfer of the parasite to the predator as a new host. Such a transition is known from other parasitic species.

Pentastomiasis in humans

In addition to their actual host species, tongue worms also occasionally attack humans (as false hosts). Humans can serve here both as an intermediate host for the larvae (in the body cavity) and as a final host for the sexually mature worm (in the nasal tract). Infections have been observed most frequently with Linguatula serrata , less often with Armillifer and Porocephalus species. Sources of infection are water or vegetables infected with dog or snake droppings (humans as intermediate hosts) or the consumption of raw or insufficiently cooked sheep or goat meat (humans as final host). Infestation with the larvae in the body cavity, secondarily also in the liver or other organs, can be completely symptom-free, but occasionally resemble lung or liver cancer. Infestation of the nasal cavities (with Linguatula serrata ) leads to severe irritation with pain, inflammation and violent sneezing (occasionally with expectoration of the parasite).

Individual species

swell

Individual evidence

  1. ^ J. Riley, RJ Henderson: Pentastomids and the tetrapod lung. In: Parasitology. 1999; 119, pp. S89-S105.
  2. ^ Sven Nikander, Seppo Saari: A SEM study of the reindeer sinus worm (Linguatula arctica). In: Rangifer. 26 (1), pp. 15-24.
  3. G. Thomas, S. Stender-Seidel, W. Böckeler: Considerations about the ontogenesis of Reighardia sternae in comparison with Raillietiella sp. (Pentastomida: Cephalobaenida). In: Parasitological Research. 1999; 85, pp. 280-283.
  4. ^ Judith M. Winch, J. Riley: Studies on the behavior, and development in fish, of Subtriquetra subtriquetra: a uniquely freeliving pentastomid larva from a crocodilian. In: Parasitology. 1986; 93, pp. 81-98. doi: 10.1017 / S0031182000049842
  5. K. Junker, J. Boomker: A check-list of the pentastomid parasites of crocodilians and freshwater chelonians. In: Onderstepoort Journal of Veterinary Research. 2006; 73, pp. 27-36.
  6. Dennis V. Lavrov, Wesley M. Brown, Jeffrey L. Boore: Phylogenetic position of the Pentastomida and (pan) crustacean relationships. In: Proceedings of the Royal Society London Series B. 2004; 271, pp. 537-544. doi: 10.1098 / rspb.2003.2631
  7. Jian Li, Fu-Nan He, Hong-Xiang Zheng, Rui-Xiang Zhang, Yi-Jing Ren, Wei Hu (2016): Complete Mitochondrial Genome of a Tongue Worm Armillifer agkistrodontis. Korean Journal of Parasitology 54 (6): 813-817. doi: 10.3347 / kjp.2016.54.6.813
  8. OS Møller, J. Olesen, A. Avenant-Oldewage, PF Thomsen, H. Glenner: First maxillae suction discs in Branchiura (Crustacea): Development and evolution in light of the first molecular phylogeny of Branchiura, Pentastomida, and other '' Maxillopoda ''. In: Arthropod Structure & Development. 2008; 37, pp. 333-346. doi: 10.1016 / j.asd.2007.12.002
  9. Waltécio de Oliveira Almeida, Martin Lindsey Christoffersen, Dalton de Sousa Amorim, Elaine Christine Costa Eloy: Morphological support for the phylogenetic positioning of Pentastomida and related fossils. In: Biotemas. 2008; 21 (3), pp. 81-90.
  10. a b Dieter Waloszek, John E. Repetski, Andreas Maas: A new Late Cambrian pentastomid and a review of the relationships of this parasitic group. In: Transactions of the Royal Society of Edinburgh: Earth Sciences. 2006; 96, 163-176.
  11. Andreas Maas, Andreas Braun, Xi-Ping Dong, Philip CJ Donoghue, Klaus J. Müller, Ewa Olempska, John E. Repetski, David J. Siveter, Martin Stein, Dieter Waloszek: The 'Orsten' — More than a Cambrian Conservat -Deposit yielding exceptional preservation. In: Palaeoworld. 2006; 15, pp. 266-282. doi: 10.1016 / j.palwor.2006.10.005
  12. David J. Siveter, Derek EG Briggs, Derek J. Siveter, Mark D. Sutton (2015): A 425-Million-Year-Old Silurian Pentastomid Parasitic on Ostracods. Current Biology 25 (12): 1632-1637. doi: 10.1016 / j.cub.2015.04.035
  13. Tommy LF Leung (2015): Fossils of parasites: what can the fossil record tell us about the evolution of parasitism? Biology Reviews 92 (1): 410-430. doi: 10.1111 / brv.12238
  14. ^ H. Krauss: Pentastomidosis. In: Albert Weber, Max Appel, Burkhard Endeis: Zoonoses: infectious diseases transmissible from animals to humans. In: ASM. 2003, pp. 402-403.
  15. ^ Dennis Tappe, Dietrich W. Büttner: Diagnosis of human visceral pentastomiasis. In: PLOS Neglected and Tropical Diseases. 2009; 3 (2), p. E320. doi: 10.1371 / journal.pntd.0000320

literature

  • Horst Kurt Schminke: Crustacea, crayfish. In: Wilfried Westheide , Reinhard Rieger (Ed.): Special Zoology. Part 1: Protozoa and invertebrates. Gustav Fischer Verlag, Stuttgart et al. 1996, ISBN 3-437-20515-3 , pp. 501-581.
  • Alfred Kaestner : Textbook of special zoology. Volume 1: Hans-Eckhard Gruner (Ed.): Invertebrates. Part 3: Mollusca, Sipunculida, Echiurida, Annelida, Onychophora, Tardigrada, Pentastomida. 5th edition. Fischer, Stuttgart et al. 1993, ISBN 3-334-60412-8 , pp. 517-543.
  • Heinz Mehlhorn (Ed.): Encyclopedic Reference of Parasitology. Biology, Structure, Function. 2nd Edition. Springer, Berlin et al. 2001, ISBN 3-540-66239-1 , pp. 472-482.

Web links

Commons : Tongue Worms  - Collection of images, videos and audio files