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The hydra have four to twelve tentacles that protrude from just outside the mouth. They feed by extending their tentacles and waiting for food to touch the tentacles. They then bring the food to their mouth, ingest and digest the organism. Anything that cannot be digested is egested. Ingestion and egestion occur through the mouth.
The nervous system of Hydra is a nerve net, which is structurally simple compared to more derived animal nervous systems. Hydra does not have a recognizable brain or true muscles. Nerve nets connect sensory photoreceptors and touch-sensitive nerve cells located in the body wall and tentacles. The structure of the nerve net has two levels:
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Ram feeding and suction feeding are on opposite sides of the feeding spectrum, where extreme ram feeding is when a predator swims over an immobile prey item with open jaws to engulf the prey. Extreme suction feeding is demonstrated by sit-and-wait predators that rely on rapid depression of the jaws to capture prey (e.g., frogfish, Antennariidae).
Krill feeding in a high phytoplankton concentration (slowed by a factor of 12). Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a specialized filtering organ that sieves out and/or traps solids.
When a hydra is cut in half, the head portion can regenerate and form a new foot with the basal disc, and the foot portion can regenerate and form a new head with the hypostome region. If a hydra was severed into smaller pieces, the middle pieces would still form a head and foot at the appropriate regions of the hydra.
Siphonophorae (from Greek siphōn 'tube' + pherein 'to bear' [2]) is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria.According to the World Register of Marine Species, the order contains 175 species described thus far.
The lophophore surrounds the mouth and is an upstream collecting system for suspension feeding. Its tentacles are hollow, with extensions of a coelomic space thought to be a mesocoel. The gut is U-shaped with the anterior mouth at the center of the lophophore. The anus, where present, is also anterior, but is dorsal to the mouth.