marine animals  |
|
|
| |
|
| Tardigrada (Bärtierchen) Tardigrada |
Tardigrada, tardigrades, around 600 species of small (mostly up to 1 mm long) aquatic Metazoa inhabiting water-containing gap systems, algae, decaying foliage, parts of plants, submerged moss pads, other invertebrates (some as parasites), etc. Depending on the climatic conditions, the number of individuals can be extraordinarily high. There are two major subtaxa, Heterotardigrada and Eutardigrada. The cylindrical body, which consists of a head and four trunk segments, is covered by a cuticle, which is often sculptured in a species-specific manner and has thread-like or wing-like appendages, which is permeable to water (see fig.). The T. are somewhat transparent and, depending on the intestinal contents and pigmentation, colourless, yellow, brownish or green. Most species have eight pairs of externally unjointed walking legs with claws. Secreted by glands, there is a calcareous stylet in the oral cavity, which serves to puncture plant or animal food, which is then sucked out. The muscular pharynx acts as a suction pump. At the transition from the midgut to the rectum, "glands" with cells that have numerous mitochondria and an enlarged surface open out in Eutardigrada, and presumably serve excretion and osmoregulation. The nervous system consists of an upper pharyngeal ganglion and a lower pharyngeal ganglion as well as an abdominal ganglia chain with four pairs of ganglia. Heterotardigrada have innervated head appendages (cirri, papillae, club-shaped structures), Eutardigrada have at least four sensory fields on the head, which may carry chemo- or mechanoreceptors. In the upper pharyngeal ganglion there is usually a simple pigment cup ocellus with a visual cell on both sides. T. have no blood circulation and no respiratory organs. |
| |
root  |
Tardigrada (Bärtierchen) Tardigrada |
| class |
|
| |
Hotel search!
