Ikeda taenioides

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Ikeda taenioides
Systematics
Trunk : Annelids (Annelida)
Class : Hedgehog worms (Echiura)
Order : Echiuroidea
Family : Ikedidae
Genre : Ikeda
Type : Ikeda taenioides
Scientific name
Ikeda taenioides
( Ikeda , 1904)

Ikeda taenioides is a representative of the hedgehog worms (Echiura) from the family Ikedidae, which is distributed in the Pacific Ocean around Japan . It is the largest known species of hedgehog worm.

features

From Ikeda taenioides only females have been described previously. The trunk, up to 40 cm long and 2 to 3 cm wide, which is usually hidden in a cave, changes shape and length continuously through contraction and extension movement, but its shape at rest becomes cylindrical with the widest point near the conical Described rear end, where it tapers slightly towards the front end with the mouth. The skin has a brownish hue over a pale yellow background and is densely covered with small, light ocher-colored papillae of varying shape and size. Towards the ends of the body these are denser, larger and more star-shaped than round. Over the trunk, with the exception of the body ends, 5 narrow longitudinal lines, equally distant from one another, of light yellow translucent color run, which are best visible when the trunk is contracted. About 1 to 1.3 cm behind the mouth there is a pair of moderately long, slightly curved, light yellow hooks on the abdomen.

The stretched out up to 150 cm long and about 1 to 1.3 cm wide, flat, ribbon-shaped, on one side convex and on the other concave, with an eyelash groove provided proboscis of the female of Ikeda taenioides has a bluish gray basic color with narrow transverse ones , deep dark brown to brownish black stripes that either run continuously from one side to the other or can be interrupted. Some of the stripes are significantly narrower than the others; on the concave side they are very numerous and dense, on the convex side they are less dense and often irregularly interrupted. On the basal section of the proboscis, about 5 to 8 cm near the mouth, the horizontal stripes are usually missing, while the basic color is grayish to light brownish and takes on a deeper hue towards the mouth. At its transition to the trunk, the proboscis forms a funnel to the mouth. The free outer end of the flat proboscis is simply rounded. A recently severed proboscis shows slow, undulating movements along its entire length. In view of the associated trunk, which is always hidden in caves, this leads to the fact that laypeople mistake it for a complete worm, the front and rear ends of which, however, cannot be distinguished.

Unlike other hedgehog worms, Ikeda taenioides has not just a few, but over 200 unpaired nephridia , the nephrostomata of which are arranged distally. The external arrangement of the longitudinal muscles outside the transverse and circular muscles, as described by Iwaji Ikeda, is now regarded as a misinterpretation.

Distribution, habitat and way of life

Ikeda taenioides lives in the western Pacific Ocean around Japan in shallow waters, but mostly below the intertidal zone, buried in the muddy underground. The female hides in caves, but stretches her trunk up to over a meter and uses it to graze microscopic food particles from the sea floor, which are fed to the mouth via the eyelash grooves on the concave side of the proboscis. The 70 to 90 cm deep caves offer good protection, apparently also from tsunamis , which wipe out a large part of the other fauna and flora.

Life cycle

The life cycle of Ikeda taenioides , of which only females have been described so far, has not yet been clarified. However, since molecular biological studies suggest a closer relationship between Ikeda taenioides and the Bonelliidae family , to which the extensively examined green hedgehog worm Bonellia viridis belongs, a sexual dimorphism is also assumed in view of the males of Ikeda taenioides not found , in the dwarf male inside the giant female Life.

Initial description

Ikeda taenioides was first described in 1907 by the Japanese zoologist Iwaji Ikeda under the name Thalassema taenioides . Japanese fishermen were only aware of the demolished Proboscides , which they believed were complete worms, but on which they could not see the mouth or anus. It was Ikeda who found the hedgehog worms belonging to it, which lived hidden in caves. The previously assigned generic name Thalassema means “sea sign” in Greek (θάλασσα, “sea”, σῆμα “sign”), while the specific epithet taenioides refers to the ribbon-like form (ταινία, “ribbon”, also “tapeworm”; εἶδος, “ Art "). Lawrence D. Wharton established the genus Ikeda in 1913 , in which he placed the type species as Ikeda taenioides and with whose name he honored Iwaji Ikeda. Until recently, Ikeda taenioides was the only species in the genus. Today, the Indian species Ikeda pirotansis , which was first described in 1962 as Ikedosoma pirotansis , is also included in this genus .

External system

More recent molecular biological investigations on nuclear and mitochondrial DNA in 49 species of hedgehog worms classify the family Ikedidae with the Bonelliidae in a clade of sexually dimorphic hedgehog worms, which is compared to a group of sexually monomorphic hedgehog worms with the families Echiuridae , Urechidae and Thalassematidae . The sexual dimorphism is said to have evolved in shallow waters.

literature

  • Iwaji Ikeda: On Three New and Remarkable Species of Echiuroids (Bonellia miyajimai, Thalassema taenioides and T. elegans). In: Journal of the College of Science of the Imperial University of Tokyo. 21, 1907, pp. 1-64.

Web links

Individual evidence

  1. ^ A b Stanley J. Edmonds: Fauna of Australia, Volume 4A. Polychaetes & Allies. The Southern Synthesis 4. Commonwealth of Australia, 2000. Phylum Echiura. P. 25, Family Ikedidae.
  2. ↑ a b Teruaki Nishikawa: Comments on the taxonomic status of Ikeda taenioides (Ikeda, 1904) with some amendments in the classification of the phylum Echiura. In: Zoological Science. 19 (10), 2002, pp. 1175-1180.
  3. ^ Philip W. Basson: Biotopes of the Western Arabian Gulf, marine life and environments of Saudi Arabia. Aramco Dept. of Loss Prevention and Environmental Affairs, 1977, p. 58.
  4. ↑ Ryutaro Goto, Shingo Sakamoto, Jun Hayakawa, Koji Seike: Underwater observations of the giant spoon worm Ikeda taenioides (Annelida: Echiura: Ikedidae) in a subtidal soft-bottom environment in northeastern Japan, which survived tsunamis of the 2011 off the Pacific Coast of Tohoku Earthquake. In: Journal of Oceanography. 73 (1), 2017, pp. 103-113.
  5. ↑ a b Ryutaro Goto: A comprehensive molecular phylogeny of spoon worms (Echiura, Annelida): Implications for morphological evolution, the origin of dwarf males, and habitat shifts. In: Molecular Phylogenetics and Evolution. 99, 2016, pp. 247-260. doi: 10.1016 / j.ympev.2016.03.003
  6. ↑ Iwaji Ikeda: The Gephyrea of Japan. In: Journal of the College of Science. Imperial University of Tokyo, Japan, 20 (4) 1904, pp. 1–87, Tables I – IV, here p. 63.
  7. ^ Lawrence D. Wharton: A description of some Philippine Thalassemae with a revision of the genus. In: The Philippine Journal of Science. 8 (4), 1913, pp. 243-270.
  8. ↑ Ikeda taenioides (Ikeda, 1904). WoRMS , 2018. Retrieved May 10, 2018.
  9. ↑ Ikeda pirotansis (Menon & DattaGupta, 1962). WoRMS , 2018. Retrieved May 10, 2018.
  10. ↑ PKB Menon, AK Datta Gupta: On a new species of Ikedosoma (Echiuridae). In: Journal Annals and Magazine of Natural History. 5 (53), 1962, p. 20.