Cestida
| Cestida | ||||||||||||
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Belt of Venus ( Cestum veneris ) |
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| Scientific name | ||||||||||||
| Cestida | ||||||||||||
| Gegenbaur , 1856 | ||||||||||||
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As cestida refers to a fine of comb jellies (Ctenophora) from the class Tentaculata . They are particularly characterized by their belt-shaped body.
The order, like the only family Cestidae, was described in 1856 by the German zoologist Carl Gegenbaur .
construction
The colorless, transparent, sometimes slightly yellowish colored animals are parallel to the line connecting the tentacles, the tentacle axis, strongly shortened, but extremely elongated in the pharyngeal axis running perpendicular to it and to the longitudinal axis of the body between mouth and statocyst , so that the body has the shape of a long, narrow one , thin ribbon, just a belt. In the longitudinal direction of the belt, the Venus belt , the species Cestum veneris , can reach a length of up to 1.50 meters, making it the largest comb jellyfish.
All eight comb ribs are present in the Cestida, but four of them are only rudiments. The other four, on the other hand, are greatly elongated and run outwards from the statocyst on the side facing away from the mouth, two each to each end of the belt. There are flagellar furrows between the individual comb platelets, which presumably transmit the impact impulses of the statocyst in a mechanical manner.
The canal system starting from the stomach, which supplies the body with nutrients, is primarily aligned parallel to the direction of the belt. From the stomach in the middle, the so-called paragastric canals run first along the throat to the mouth side and then along the long side of the belt outwards to the belt ends. There they unite with the meridional canals, which are also parallel to the longitudinal side of the belt, but in the equatorial plane, i.e. in the middle between the side facing away from the mouth and the side facing away from the mouth.
Cestida species have two rudimentary tentacles that arise on the side of the mouth. There are also two grooves on each side of the mouth that run along the entire length of the belt to the end of the belt, from which numerous tentils , threads covered with adhesive bodies ( colloblasts ) emanate.
distribution and habitat
Cestida live in tropical and subtropical waters as part of the macroplankton .
nutrition
The tentils, which arise along the entire belt on the side of the mouth, flow transversely to the belt axis to the side facing away from the mouth and thus form an extensive curtain on which zooplankton cling, which is then transported to the mouth by flagella located between the bases of the tentils.
Your tentille system is therefore the - mostly dominant - alternative to catching prey with the reduced tentacles.
For animals like the Cestida, which feed on food particles and plankton suspended in water, the belt-like body shape may represent an evolutionary adaptation to increase the catching area, which allows them to eat without interruption in plankton-rich waters.
Locomotion
Cestida species can use their comb ribs to float almost silently on the spot or to glide through the water with the mouth side first. Wave-like snaking movements of the whole body caused by muscles also allow them to swim actively.
Reproduction
All species are hermaphrodites , so they have male and female gonads and reproduce sexually. Self-fertilization is possible, but apparently less common than cross-fertilization.
Tribal history
Fossil representatives of the Cestida have not survived. A comparison with other representatives of the modern comb jellyfish provisionally suggests that they are related to Cestida, Thalassocalycida and Lobata .
Systematics
A distinction is made between two types, which are divided into two genera :
- The Venus belt ( Cestum veneris ) reaches a body length of up to 1.50 meters. With him, the longitudinal meridional canals arise below the corresponding rows of ridges on the side of the animal facing away from the mouth and only run from there into the equatorial plane.
- The type Velamen parallelum , in which the meridional canals start directly in the equatorial plane of the animal from radial canals, is much smaller at around 20 centimeters in length.
literature
- Matsumoto, GI, Harbison, GR, In situ observations of foraging, feeding, and escape behavior in three orders of oceanic ctenophores: Lobata, Cestida, and Beroida , Journal of Marine Biology, 117 , 1993, p. 279
- Stretch, JJ, Observations on the abundance and feeding behavior of the cestid ctenophore, Vestamen parallelum, Bulletin of Marine Science, 32 , 1982, p. 796
