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| Chaetognatha (Pfeilwürmer) Chaetognatha |
The German name is based on arrow-shaped structures of the head of many species. The animals are transparent and possess a cuticula, which is formed only in a few places. The body is torpedo-shaped and divided into head, trunk, and tail. Arrowworms have one or two pairs of lateral fins for stabilizing the lag and a tail fin. The fins are stiffened by fin rays and are primarily understood as hovering devices (buoyancy surface enlargement), especially as some species can raise and lower the jelly mass in the fins. On the head are hook-shaped gripping bristles of chitin, from which the term bristle-pine (Chaetognatha) derives. These bristles are used for hunting and are fed during swimming. Above the mouth are teeth. All species are zwittrig. The nervous system consists of a brain, a ganglion on the stomach, and nerves on the body surface. Eyes are usually also present. Breathing, circulatory or excretory organs are missing. The metabolism is mostly operated directly over the skin. Some species have the debilitating nerve plexus tetrodotoxin (TTX), which is formed in glandular cells. These species include Flaccisagitta lyra, Parasagitta elegans, Eukrohnia hamata and Zonosagitta nagae. In a study of these species, the known bacterium Vibrio alginolyticus was isolated as TTX-producing. It is assumed that these bacteria are responsible for the formation of poison and thus an association or symbiosis between these bacteria and the arrowworms [4]. However, the detection of bacterial tetrodotoxin formation has also been questioned. [5] [6] Protection from the formation of tetrodotoxin is widespread in the animal kingdom. For example, this protective mechanism is also found in ball fishes and blue-coiled octopuses. |
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Chaetognatha (Pfeilwürmer) Chaetognatha |
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