Nectonema agile
| Nectonema agile | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Nectonema agile | ||||||||||||
| Verrill , 1879 |
Nectonema agile is the name of a marine strings worm - kind from the family of Nectonematidae that in the Atlantic Ocean and the Mediterranean lives and in decapods parasitized .
features
Nectonema agile is about 0.3 mm to 1 mm thick and, according to the German zoologist Otto Bürger (1891), 8 cm to 22 cm long. The French authors Noël and Maran (2018), on the other hand, give lengths of 5 cm to 10 cm (occasionally 20 cm) for the males and 3 cm to 6 cm for the females, which means that the animals, like all string worms, are very thin compared to their length, are thread-like (filiform or nematomorphic). The longest individual found so far, however, is a 59 cm female found in an American lobster . The string worm has a cylindrical shape and a smooth body surface, whereby it is slightly flattened at both ends and the head end is also rounded and conical. The animal has two rows of hair-shaped swimming bristles along its entire body with the exception of a longer head section and a shorter tail section. In its host, the string worm is light, cream-colored to beige in color, but it takes on a dark color after it has left the host animal. A characteristic characteristic of the species is that the front third of the body is rotated around the longitudinal axis, namely by 90 ° at the outermost front end. The rear end appears cut off perpendicular to the body axis in the female. The differences between males and females are small, apart from body length. In both sexes, the genital opening is at the extreme end of the body. The male, however, is covered with scales at the rear end of the body.
Distribution, habitat and hosts
Nectonema agile is widespread in the Atlantic Ocean on the coasts of North America (South Canada , North USA ) and Europe as well as in the Mediterranean , the English Channel and the North Sea . The animals move as sexually mature animals, swimming freely in snaking movements near the surface of the sea, where they alternately contract their left and right longitudinal muscles. The young parasitize a wide variety of decapods such as shrimps , crabs and lobsters . Significant prevalences can sometimes be achieved, in certain populations of the American edible cancer Cancer magister between 2% and 21%. The parasite lives mainly in the thorax of the infected cancer.
Development cycle
Nectonema agile is single- sex. Males and females actively seek out each other in the water. The approximately 36 to 40 μm large, spherical and smooth eggs are fertilized in the course of copulation in the female and, after oviposition, form long conical spines on their surface when they come into contact with the sea water. From the prickly eggs hatch about 0.3 mm to 0.4 mm long transparent larvae without an esophagus, but with a proboscis on which two wreaths of hooks (but no stilettos as in freshwater string worms) sit. The invasion of the larvae into the host crabs has not yet been observed, but it is considered likely that the larvae can be swallowed by the crabs. The hooked trunk apparently serves to pierce the host's intestinal wall so that the string worm can live in the body cavity, the host's mixocoel . Here the larva, which resides in the thorax in particular, grows into a long worm with an esophagus (but without a mouth), taking in nutrients from the host through its skin. While still in the host, the animal develops gonads , a rudimentary bowel and swimming bristles. After all, the string worm can occupy much of the interior of the host. When it is fully grown, it pierces the host's synovial membrane and ends up in the open sea. As a rule, the skin between the carapace and the first segment of the abdomen is likely to be penetrated. Depending on the size of the host, it is (more rarely) killed, castrated or only damaged to a limited extent. The adult string worm no longer eats anything, but instead seeks out its sexual partner by swimming with the aid of its swimming bristles. After copulation, new eggs are laid, from which new larvae emerge, while the parent animals die.
literature
- Addison Emery Verrill (1879): Notice of recent additions to the marine fauna of the east coast of North America. American Journal of Science and Arts (3) 17, pp. 309-315.
- Otto Bürger (1891): To the knowledge of Nectonema agile Verr. Zoological Yearbooks, Department of Anatomy and Ontogeny of Animals 4, pp. 631–652.
- Henry Baldwin Ward (1892): On Nectonema agile Verril. The American Naturalist 26 (312), pp. 1037-1041.
- Thilo Krumbach: Handbook of Zoology. Second volume, first half - Vermes Amera. Walter de Gruyter, Berlin 1923. Nematomorpha , p. 406.
- Thérèse Feyel (1930): Sur l'oogenése du Nectonema agile Verr. Comptes rendus des séances de la Société de biologie et de ses filiales Société de biologie, Paris 82, pp. 681–683.
- Thérèse Feyel (1936): Researches histologiques sur Nectonema agile Verr. Etude de la forme parasitaire. Archives d'Anatomie Microscopique 32, pp. 197-234.
- José Bresciani: Nematomorpha. In: Frederick W. Harrison, Edward E. Ruppert (Eds.): Microscopic Anatomy of Invertebrates, Aschelminthes. Vol. 4. Wiley, New York 1991, pp. 197-218, here: Nectonema , p. 217.
- Andreas Schmidt-Rhaesa, Gerhard Pohle, Julien Gaudette, Victoria Burdett-Coutts (2013): Lobster (Homarus americanus), a new host for marine horsehair worms (Nectonema agile, Nematomorpha). Journal of the Marine Biological Association of the United Kingdom 93 (3), pp. 631-633.
Web links
- Pierre Noël, Vincent Maran: Nectonema agile Verrill, 1879. Données d'Observations pour la Reconnaissance et l'Identification de la faune et la flore Subaquatiques (DORIS), 7 February 2018.