Sclerites ( ancient Greek σκληρός sklēros , German 'hard' ) are hard parts of invertebrates , especially the arthropods in their exoskeleton, sponges and octocorallia in their soft parts. The term does not refer to bony skeletal parts or teeth of vertebrates or shells of molluscs .
In 1985 , Stefan Bengtson coined the term scleritoma for the entirety of the sclerite of an organ (e.g. radula) or the skeletal system of a non-vertebrate animal (e.g. all the skeletal needles of a glass sponge) . This term is rarely used, but is used.
Sclerits in arthropods are by sclerotization in crustaceans also often calcification hardened individual panels of the exoskeleton . Sclerites can be isolated in softer cuticles. They often cover the entire integument and are articulated to one another by membranous seams, they can also form partially immovably connected, reinforced shells (e.g. head capsules in insects). A distinction is made between tergites ( dorsal ), sternites ( ventral ) and pleurites ( lateral ). Sclerites form attachment points for the muscles on the exoskeleton, which are known as apodemes .
As skeletal needles ( Latin spiculum 'sting', plural spicula ), sclerites can be used for stability and as protection against eating by flowered animals , sponges , echinoderms , molluscs and tunicates . While many sclerites represent microscopic fine structures, the largest measure up to three meters.
Spicula are lime (made of calcite , CaCO 3 ) or silica needles (made of silica , SiO 2 ) in the body of many marine non-mollusc groups to stabilize their body shape, the needle shape is suitable for deterring larger predators. In addition to the main mineral content, they contain complex organic substances.
After the soft corals die, a massive skeleton does not remain, as is the case with the hard corals , only the sclerites remain on hard parts. In the leather coral Sinularia leptoclados, however , the sclerites in the colony base are so densely packed that reef structures up to six meters high can arise from the residues. It is the only reef-forming soft coral.
The skeletal needles of the sponges ( sponge needles ) are either lime needles ( lime sponges ) or silica needles (silica sponges : glass sponges ).
Skeletal remains of the siliceous sponges can remain as so-called rattle stones after the animals die. In some groups of sponges, the individual sclerites merge into a rigid skeleton.
In the horn silica sponges , collagen-like spongin fibers largely replace the skeletal needles.
Some glass sponges form a particularly large spiculum that is used to anchor in the ground. Even in English, this is sometimes referred to as a stake needle . The hook-shaped sclerites of the carnivorous horned silica sponge Chondrocladia turbiformis adapt to special functions .
The glass sponge Monorhaphis chuni forms only a single anchoring spiculum, but the largest sclerite with a length of up to three meters. The annual growth can be determined by determining the oxygen isotopes and the distribution ratio of calcium to magnesium. While the thickness of the 'annual rings' allows conclusions to be drawn about the sea water temperature at that time, their sequence provides a climate archive and their counting gives the age reached. In a find in the East China Sea, an age of 11,000 ± 3,000 years was determined.
Some molluscs (especially nudibranchs ) often have calcified spicules embedded in their tissue to protect them from predators. The hard structures of teeth in the radula of molluscs are also known as sclerites.
Tunicates, especially sea squirts , show a high degree of variability in their microspicules. In stove Mania momus two calcified Spiculatypen are: 1.5-2.5 mm long, spindle-shaped, each with 100 or more rows of overlapping micro-tips, as well as smaller spicules, each with 20-40 rows of non-overlapping microdots that are anchored by means of a spider-shaped structure in the foot of the animal .
Typical of the echinoderms are often connected skeletal plates, which are called ossicles. Small and isolated ossicles embedded in soft tissue that serve to strengthen tissue are also called sclerites.
Aid for taxonomic classification
Sclerites often have a shape and size characteristic of a species and are therefore an important tool for a taxonomic classification (identification of species). The shape of the sclerite is also of forensic importance when determining the species, for example of blowfly larvae in parts of the body.
When marine invertebrates disintegrate, their individual clerites are often released; they then become part of the oceanic detritus and part of the coral sand, or the individual particles fill gaps in the substrate. The determination of fossil sclerites allows taxonomic assignments and thus often conclusions about sea depth and temperature, comparative analyzes can also provide conclusions about marine species change , sea level fluctuations and climate change and thus allow a climate chronology .
- ↑ a b Herder Lexicon of Biology , Seventh Volume praealpin bis Spindelstrauch, Spectrum Academic Publishing House, Heidelberg / Berlin / Oxford 1994, ISBN 3-86025-156-2 , p. 440.
- ^ NJ Butterfield: An early Cambrian radula. In: Journal of Paleontology , Volume 82, No. 3, 2008, 543-554, doi : 10.1666 / 07-066.1 .
- ^ S. Bengtson: Taxonomy of disarticulated fossils. In: Journal of Paleontology , Vol. 59, No. 6, 1985, pp. 1350-1358.
- ↑ Simon Conway Morris: The Burgess Shale Fauna and the Early Evolution of Animals. In: Biology in our time , Volume 22, No. 5, 1992, pp. 256-263, doi : 10.1002 / biuz.19920220510 .
- ↑ JB McClintock: Investigation of the relationship between invertebrate predation and biochemical composition, energy content, spicule armament and toxicity of benthic sponges at McMurdo Sound, Antarctica. In: Marine Biology , Vol. 94, No. 3, 1987, pp. 479-487.
- ↑ http://geology.gsapubs.org/content/25/4/303.short
- ^ WC Jones: The composition, development, form and orientation of calcareous sponge spicules. In: Symp. Zool. Soc. London , Volume 25, 1970.
- ↑ Heidi Zanker: Chemical and ecological studies on North Sea sponges. (PDF; 6.9 MB) Diss. University of Frankfurt / Main, 2005.
- ↑ Xiaohong Wang, Heinz C. Schröder, Werner EG Müller .: Giant siliceous spicules from the deep ‐ sea glass sponge Monorhaphis chuni. In: International Review of Cell and Molecular Biology , Volume 273, 2009, pp. 69-115, doi : 10.1016 / S1937-6448 (08) 01803-0 .
- ↑ Klaus Peter Jochum et al .: Siliceous deep-sea sponge Monorhaphis chuni: A potential paleoclimate archive in ancient animals. In: Chemical Geology , Volume 300, 2012, pp. 143-151, doi : 10.1016 / j.chemgeo.2012.01.009 .
- ↑ Riccardo Cattaneo-Vietti et al .: Mineral composition of nudibranch spicules. In: Journal of Molluscan Studies , Volume 61, No. 3, 1995, pp. 331-337.
- ^ Magdalena Lukowiak: First record of late eocene Ascidians (Ascidiacea, Tunicata) from Southeastern Australia. In: Journal of Paleontology , Volume 86, No. 3, 2012, pp. 521-526, doi : 10.1666 / 11-112.1 .
- ^ G. Lambert, CC Lambert: Spicule formation in the solitary ascidian, herdmania momus. In: J. Morphol. Volume 192, No. 2, 1987, pp. 145-159, doi : 10.1002 / jmor.1051920206 .
- ↑ Amelia Ocaña Martín, J. Manuel Tierno de Figueroa, Rogelio J. Palomino-Morales (2006): Sclerites in Different Tissues of Mediterranean Echinodermata. Zoological Science Vol. 23, Issue 6: 557-564 doi : 10.2108 / zsj.23.557
- ↑ C. Reiter, G. Wollenek: To determine the species of maggots of forensically significant blowflies. In: Zeitschrift für Rechtsmedizin , Volume 90, No. 4, 1983, pp. 309-316.