marine animals  |
|
|
| |
|
| Acanthocephala (Kratzwürmer) Acanthocephala |
The scratchworms have a three-part articulated body. In this case, the trunk (metasoma), which houses the entire internal organs, is the largest section, while the neck and the trunk or the scolex (commonly referred to as the presoma) are only a small part of the body length. A belly and backside can not be determined either by the scratching worms either on the outside or on the basis of the organ layers; The determination of the position was determined by them on the basis of the organs of the closely related Bdelloida, in which the gonads always lie on the ventral side and the brain on the posterior side. The number and the arrangement of the cells during the development is arttypical and stable (Eutelie) in most species, only the number of germ cells is constantly increasing. In most species the females are significantly longer and stronger than the males. The trunk is equipped with rearward-facing hooks which serve to attach the intestine of the host and to which the animals owe their scientific name Acanthocephala. In many species, especially the representatives of the Palaeacanthocephala and the Eoacanthocephala, there are also hooks or unbentheled thorns on the neck, which represents the transition between the trunk and the trunk. The trunk is mostly smooth-walled or wrinkled; In some species, such as Mediorhynchus taeniatus, it possesses a pseudo-segmentation, which only gives it the appearance of a segmented worm. The tegument can be up to two millimeters thick in the very large species and, like many other tissues of these animals, is formed by a syncytium. The basis for this cell cluster is approximately 6 to 20 individual cells in most species, whose adjacent cell membranes dissolve and thus form a tissue with many small or distinctly very large cell nuclei. The cell nuclei enlarge in the course of the development and become polyploid by permanent mitoses, in many species they ramify themselves and reach diameters of up to two millimeters. Especially in large species the cell nuclei disintegrate without mitotic division into many small fragments. In the epidermis there are also collagen fibers, which on the outer side are predominantly parallel to the direction of the body and in the lower layers, thus stabilizing the epidermis. The outermost region is denser than the inner one, but does not form an armor. This layer is traversed by numerous invaginations which form a complex lacuna system, which is used for nutrition. |
| |
root  |
Acanthocephala (Kratzwürmer) Acanthocephala |
| class |
|
| |
Hotel search!
