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Cnidarian sexual reproduction often involves a complex life cycle with both polyp and medusa stages. For example, in Scyphozoa (jellyfish) and Cubozoa (box jellies), a larva swims until it finds a good site, and then becomes a polyp.
Unlike some other cnidarian groups, the lining of the central cavity lacks stinging nematocysts, which are found only on the tentacles and outer surface. All colonial hydrozoans also include some polyps specialized for reproduction. These lack tentacles and contain numerous buds from which the medusoid stage of the life cycle is produced.
The cnidae, the explosive cells characteristic of the Cnidaria and used in prey capture and defence, are of a single type, there being nematocysts but no spirocysts or ptychocysts. [4] In contrast, the anthozoan life cycle involves a planula larva which settles and becomes a sessile polyp, which is the adult or sexual phase. [11]
There are four stages that were found to describe the inverted life cycle of the Turritopsis nutricula: healthy medusa (where the T.nutricula would swim actively), unhealthy medusa (the T. nutricula was not able to swim), four-leaf clover, and cyst (would produce the polyp morphologically). [8]
The Scyphozoa are an exclusively marine class of the phylum Cnidaria, [2] referred to as the true jellyfish (or "true jellies"). The class name Scyphozoa comes from the Greek word skyphos (σκύφος), denoting a kind of drinking cup and alluding to the cup shape of the organism. [3] Scyphozoans have existed from the earliest Cambrian to the ...
Similarities between myxozoan polar capsules and cnidarian nematocysts had been drawn for a long time, but were generally assumed to be the result of convergent evolution. Taxonomists now recognize the outdated subgroup Actinosporea as a life-cycle phase of Myxosporea. [25]
Like many Hydrozoa, Velella velella has a bipartite life cycle, with a form of alternation of generations. The deep blue, by-the-wind sailors that are recognized by many beach-goers are the polyp phase of the life cycle. Each "individual" with its sail is really a hydroid colony, with many polyps that feed on ocean plankton.
Clytia hemisphaerica is a small hydrozoan-group cnidarian, about 1 cm in diameter, that is found in the Mediterranean Sea and the North-East Atlantic Ocean. [1] Clytia has the free-swimming jellyfish form typical of the Hydrozoa, as well as vegetatively propagating polyps.