Crown jellyfish

Crown Jellyfish are any of the species of jellyfish in the taxonomic order Coronatae. There are eight Crown jellyfish families (Atollidae, Atorelliidae, Collaspididae, Linuchidae, Nausithoidae, Paraphyllinidae, Periphyllidae, and Tetraplatidae).

Anatomy
Crown Jellyfish have a cone shaped swimming bell that reach 20cm tall and 17cm in diameter, however zoological specimens from the ocean usually are less than 5cm in size. The swimming bell of specimens is transparent and reveals the reddish brown stomach. However, in large specimens, the swimming bell is cloudy or not clear and is a reddish brown color. The swimming bell has 16 deep notched lappets, in addition the tentacles appear from the bell surface, and they repeat the pattern of three tentacles and one rhopalium (a sensory structure that lies in an indentation in the edge of the bell) . The crown jellyfish is found at depths below 900m (3000 ft), where the water temperature is really cold. Also, the Crown jellyfish undergoes straight up and down movement from deep water in the daytime to shallow water at night in order to follow their prey, or catch their prey. They will swim downward when exposed to a bright light. Crown Jellyfish produce plentiful amounts of mucus which has the capacity of bearing stinging cells. [international wildlife encyclopedia; multiple authors]

Reproduction
Fertilized eggs are released in deep water, where they drift, not feeding for several months. Eggs and larvae are present all year round in Lurefjorden, Norway, suggesting a lack of seasonality in the relatively constant environment of the deep ocean. The larvae develop directly into medusae without polyp or ephyra stages. After fertilization and initial growth, a larval form, called the planula, develops from the egg. The planula is a small larva covered with cilia. It settles onto a firm surface and develops into a polyp. The polyp is cup-shaped with tentacles surrounding a single orifice, resembling a tiny sea anemone. After an interval of growth, the polyp begins reproducing asexually by budding. Most crown jellyfish have a lifespan of two and a half months; few live longer than six months. Their sexes separate in breeding season which is summer; tiny planula larvae are released and then settle, developing into colonies of polyps; each polyp buds off and develops into jellyfish.[international wildlife encyclopedia; multiple authors]

Ecology
Crown Jellyfish are mostly found at mesopelagic depths (between 200m and 1000m, called the twilight zone) in all oceans worldwide, but mostly in the Pacific Ocean and Atlantic ocean. Furthermore, they are mostly found in the New Guineas or the ocean nearby. Populations a magnitude greater than the open ocean have been found in Norwegian fjords, especially Lurefjorden. They live in depths below 900m where the water temperature is only 7 degrees Celsius (45o F). The diet of the Crown Jellyfish is plankton up to 1/5 inch in diameter, including diatoms, algae, invertebrate eggs, mollusk larvae and so on. For feeding, they hold their tentacles up alongside the bell, swim downward about 10m and then drift upward. At that moment, the tentacles quickly move to the mouth, coil and then enter the stomach. Since Crown jellyfish are carnivorous, many of them capture fish, shrimp and other animals on their tentacles. They paralyze the prey with their stinging cells and transfer it to the mouth. Jellyfish also have different ways of swimming, for example, crown jellyfish swim by rhythmic pulsations of the umbrella, or bell.[international wildlife encyclopedia; multiple authors] Swimming is coordinated by a simple nervous system and by sense organs. 

Body structure
Their bodies are 95-99 percent water based jelly, so that the whole body contains less than 5 percent organic matter. The stings of jellyfish come from the many stinging cells, nematocysts, which shoot out a venom-laden thread when touched. The most venomous jellyfish belong to the Cubomedusae, named for their squarish shape. Around their body, the organs lie in pouches in the digestive cavity but show through the transparent bell. From the base of each polyp, stolons grow out and new polyps develop on them.[international wildlife encyclopedia; multiple authors]