Screw table

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Screw table
Screw table gozo.jpg

Screw table ( Sabella spallanzanii )

Systematics
Order : Canalipalpata
Subordination : Sabellida
Family : Featherworms (Sabellidae)
Subfamily : Sabellinae
Genre : Sabella
Type : Screw table
Scientific name
Sabella spallanzanii
( Gmelin , 1791)

The Sabella Spallanzanii , scientific name Sabella spallanzanii , belongs to the genus Sabella in the class of polychaete (Polychaeta) and is in the Mediterranean vernacular. It is one of the largest members of the Sabellidae family. The screw table is a filter feeder and feeds primarily on plankton . It forms a parchment-like tube, which it inhabits permanently, mostly on a hard substrate .

Occurrence

Sabella spallanzanii is native to the Mediterranean Sea and the Atlantic coast of Europe. In other parts of the world it was brought in from the Mediterranean by humans, presumably as larvae in the ballast water of ships or as adults on the hull, and is sometimes considered to be an invasive neozoon . In addition to early information from the 19th century on the Brazilian coast, the species occurs widespread in Australia, later it was also registered by New Zealand.

In Australia, S. spallanzanii is considered an invasive species. It was first spotted in Port Phillip Bay in several colonies with 1 to 30 individuals and was later found in other areas of Australia such as Cockburn Sound and Spencer Gulf . The distribution of the species also has economic consequences, as the screw table is increasingly found as bycatch in scallop catches and has to be sorted out from this. In addition to these economic consequences, there are also ecological problems in Australia, as S. spallanzanii competes for space with other native, benthic organisms. The screw table occurs at a depth of 1 m to 30 m and prefers nutrient-rich waters with little currents and waves. They are mostly found in colonies with a high number of individuals (150–300 individuals per square meter) but also sporadically, especially in flatter areas.

morphology

Sabella spallanzanii with a screwed tentacle crown

The screw table has a body divided into two parts, the trunk section (thorax) and the abdomen (abdomen). The thorax consists of 8 to 9 segments , the abdomen of 50 to 200 segments . The body is usually enclosed in the rigid but flexible tube. The semi-transparent tube in which the polychaete resides is formed by mucus and mud from the environment that is secreted by the body and can be covered with silt or shell fragments. The flexible, elastic tube can be 12 to 70 cm long, exceptionally up to 80 cm long. The length of the body is usually similar to that of the tube. The base of the tube usually forms a U-shaped bend and is anchored to the substrate with this; the lower end can be encased in a soft substrate.

As is typical for the relationship, two leaf-shaped, widened appendages sit at the front end, forming a crown set with tentacles. In the species these are only symmetrical in young animals, but strongly asymmetrical in adult worms. As observations in various show aquariums have shown, both the left and the right branch can become a much larger tentacle screw, while the other remains short. So this is a racemic right-left feature. This helical structure is an important species feature; it does not occur in any other species in Australia, for example. The diameter of the spread out tentacle crown reaches 10 to 15 centimeters. In the event of a fault, this can be pulled together and drawn into the protective tube. The color of the tentacles is different - whitish, yellow, or orange, with darker, red-brown to purple stripes. The species can be distinguished from its sister species, peacock feather worm ( Sabella pavonina ), by the strongly asymmetrical, screwy tentacle crowns; in addition, the first segment is just as long, not twice as long, as the following body segments.

In addition to feeding, the crown also has a respiratory function, but is not an essential part of the respiratory system, because even without it, gas exchange can continue to take place to a lesser extent.

In contrast to many annelids and even sabellids, Sabella spallanzanii has a very high regenerative capacity and can regenerate both areas of the front and rear of the body. In addition, if they are injured or severed completely by fish or other marine life, they can completely regenerate the crown. First, wound closure begins with muscle contractions, which is followed by the formation of a transparent blastema , which finally forms into a regenerative bud. In the case of injuries to the body, the recovery time can vary between two and four days. The duration of the regeneration depends on the season. In summer it is shorter than in winter, as the temperature of the water plays an important role.

Ingestion

Each tentacle has two rows of ciliate, called pinnulae, appendages that contribute to the feather-like shape. The pinnulae create a continuous flow of water through the tentacle crown, which directs particles into the crown so that they can be caught by the eyelashes. The particles mostly consist of plankton but also contain bacteria that are ingested by S. spallanzanii . These particles are then sorted at the base of the tentacles and directed into the mouth opening.

behavior

The worms move in the tube, constantly renewing the water in the tube. In this way, more and more oxygen-rich water is brought into contact with the worm. This is guaranteed by a continuous flow of water that can flow through the pipe from the front opening to the rear opening and vice versa. This is possible even when the worm has withdrawn in its tube. The worm occasionally stops the water from circulating. However, these interruptions in the water flow last a maximum of 15 minutes. Then S. spallanzanii initiates the renewed circulation of the water.

Reproduction and larval development

S. spallanzanii is sexually separated and can only reach sexual maturity from a height of 15 centimeters, whereby the males are usually shorter than the females. Both sexes have no separate ovaries or testes, which is why the maturation of the oocytes and spermatocytes takes place in the coelom . The long process of maturation of oocytes begins shortly after spawning in February (Mediterranean) or August (Australia) and lasts nine months. When the eggs are fully ripe, they reach a diameter of 250 millimeters. In contrast, the maturation of the spermatocytes is much shorter and does not begin until seven months later than the oogenesis. A large number of mature spermatozoa are already present three months later. According to Giangrande et al. the eggs are fertilized in the tube, but it is still unclear whether this takes place in the worm or between the worm and the tube. The fertilized eggs are shed from the tube in a mucus.

After the first 24 hours, the embryos develop into free-swimming trochophora larvae, which hatch out of the egg shell and develop paired eye spots over the next 12 hours. After 72 hours, two new segments begin to form, one of which has bristles. This stage takes about two weeks until it settles, mostly in crevices of rock. Two more bristle-bearing segments are formed in these two weeks. The anal opening occurs ten days after settlement. Then the manufacture of the tube begins.

Use

As already mentioned, S. spallanzanii is a filter feeder and feeds on plankton, but also bacteria. This ability to take in bacteria can be used to control the water. The worm can ingest the bacteria that are in the water and in doing so enables these bacteria to be identified, even if they are only in a very low concentration in the water. In addition, with the growing threat to marine habitats, S. spallanzanii could serve as a bio-indicator to identify and control bacterial contamination . The bacteria found in the worm include the following: a. also human pathogenic species. This shows that S. spallanzanii could serve not only as a bio-indicator, but also as a tool to eradicate such pathogenic species in contaminated regions.

Individual evidence

  1. ↑ a b Currie, DR, McArthur, MA & Cohen, BF (2000): Reproduction and distribution of the invasive European fanworm Sabella spallanzanii (Polychaeta: Sabellidae) in Port Phillip Bay, Victoria, Australia. Marine Biology 136, 645-656. ( Online )
  2. ^ Fox, HM (1938): Function of the Tube in Sabellid Worms. Nature 141, 163-163.
  3. ↑ Lauren M. Fletcher (2014): Background information of the Mediterranean fanworm Sabella spallanzanii to support regional response decisions. Cawthron Institute, Nelson, New Zealand, Cawthron Report No. 2479A, 35 pp.
  4. ↑ Maria Capa, Pat Hutchings, M. Teresa Aguado, Nathan J. Bott (2011): Phylogeny of Sabellidae (Annelida) and relationships with other taxa inferred from morphology and multiple genes. Cladistics 27: 449-469. doi: 10.1111 / j.1096-0031.2010.00341.x
  5. ^ PJ Hayward, JS Ryland: Handbook of the Marine Fauna of North-West Europe. Oxford University Press, 2017. ISBN 978-0-19-954944-3 . Determination table on page 221.
  6. ^ A b Wells, GP (1951): On the Behavior of Sabella. Proceedings of the Royal Society B 138 (891), 278-299. doi: 10.1098 / rspb.1951.0023
  7. ↑ Licciano, M., Murray, JM, Watson, GJ & Giangrande, A. (2012): Morphological comparison of the regeneration process in Sabella spallanzanii and Branchiomma luctuosum (Annelida, Sabellida). Invertebrate Biology 131, 40-51. doi: 10.1111 / j.1744-7410.2012.00257.x
  8. ↑ Clapin, G. & Evans, DR (1995): The status of the marine Introduced fanworm Sabella spallanzanii in western Australia: a preliminary investigation. Crimp Technical Report, CRIMP, Hobart, Tasmania (Australia), July 1995 No. 2, 34 pp.
  9. ↑ Westheide, W. & Rieger, R. (2006): Special Zoology. Part 1: Protozoa and invertebrates. 2nd Edition. Spectrum Academic Publishing House. ISBN 978-3-8274-1575-2
  10. ↑ a b Giangrande, A., M. Licciano, M., Pagliara, P. & Gambi, MC (2006): Gametogenesis and larval development in Sabella spallanzanii (Polychaeta: Sabellidae) from the Mediterranean Sea. Marine Biology 136, 847-861. doi: 10.1007 / s002279900251
  11. ↑ Stabili, L., Licciano, M., Giangrande, A., Fanelli, G. & Cavallo, RA (2006): Sabella spallanzanii filter-feeding on bacterial community: Ecological implications and applications. Marine Environmental Research 61, 74-92. doi: 10.1016 / j.marenvres.2005.06.001

Web links

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