تعبير انجليزي عن
حيوان بحري
قنديل البحر في
الإنجليزية
موضوع بالانجليزي
عن حيوان بحري
أريد موضوع تعبير
عن حيوان باللغة الإنجليزية مهم
حيوان بحري لافقاري
رخوي يعيش داخلها
قنديل البحر (بالإنجليزية: jellyfish)
اكتب تقرير عن حيوان بحريWrite a report a bout marine animal
Paragraph : Write
الانجليزية •حيوان
مهدد بالانقراض باللغة الانجليزية • تعبير عن الدب القطبي بالانجليزي
تعبير انجليزي عن
حيوان بحري
موضوع عن سمك القرش
بالانجليزي
موضوع انجليزي عن
الكائنات البحرية
بحث عن قنديل البحر
باللغة الانجليزية
بحث عن الحيوانات
البحرية باللغة الانجليزية
بحث عن حيوان بحري
باللغة الانجليزية
تعبير عن حيوان
بالانجليزي
The term jellyfish is a vernacular name
designating the free forms of many decidial groups and thus opposing polyps,
sessile forms. Jellyfish are usually predatory, they paralyze their prey with
their cnidocytes and may possess very elaborate sensory structures such as
ocelli, gathered within derhopalies. Some jellyfish belonging to the Cubozoape
class can be deadly to humans. In the life cycle of certain groups of
cnidarians, the jellyfish form can alternate with the polyp phase, but others
live only in the jellyfish state. Although mostly found in salt water, it is
possible to observe certain types of jellyfish in fresh water.
There are about 1,500 species of
jellyfish recorded in the early nineteenth century, mostly dehydromedos. In
view of the recent results of molecular phylogeny, jellyfish are considered as
a characteristic of one of the two decidial groups, called Medusozoa (composed
of the classes Cubozoa, Scyphozoa and Hydrozoa). The other group being the
Anthozoa2. However, the exact evolutionary origin of the medusa form is still
poorly understood.
The majority of species feed on
microplankton trapped by their marginal or peri-shadow tentacles, shrink
filaments attached to the edge of the parasol. Some species, such as in the
order Rhizostomeae, have welded mouth extensions without a distinct buccal
orifice, feeding at numerous and tiny oral orifices on the coalescent buccal
arms, and supplement themselves with sugars thanks to symbiotic algae Who live
in these arms. Others feed by capturing larger prey (copepods, larvae and fish
eggs, fish a few cm in length). Some jellyfish fall over, with the umbrella
facing upwards, waiting for the plankton falling to the bottom to fall into
their oral cavity21.
In their optimal search strategy for
food, jellyfish practice both passive hunting and hunting. These strategies
differ depending on the size and shape of the umbrella, the number, size and
arrangement of the tentacles22.
Reproduction
Some jellyfish may bud, other jellyfish
on the edge of the umbrella but the majority of asexual reproduction is done
from the polyp. At the moment of sexual reproduction, jellyfish become genuine
"floating gonads", all their food being committed to producing these
glands. Sex cells are differentiated in the gonads that develop around the
manubrium in anthomedos, along the radial canals in leptomedos and
trachymeduses, in genital pockets connected to the stomach in the
scyphomeduses. They release into the water column the gametes (spermatozoa for
male jellyfish, ova for females) which disperse in the ocean and fertilize the
eggs: fertilization is external, with the exception of Stygiomedusa gigantea
(en) or Of Aurelia aurita which are viviparous. Once reproduction is assured,
jellyfish die. This life cycle is a semi-parity which is favored by the short
duration of the free form, which can correspond to a specific energy
strategy23. By dispersing the eggs, they contribute to the colonization of new
geographical areas. The embryonic development is marked by different stages and
leads to the formation of a ciliate larva, the planula. The polyps then line
the bottom of the ocean. These polyps develop differently depending on the
species. Some can develop only after half a century. More generally, a
significant change must take place (eg change in temperature, oxygen, thunder)
to allow them to release the jellyfish thus formed24.
Human consumption
A dozen species of jellyfish are eaten in
Asia, particularly in Japan (kurage), especially cut into strips in the form of
salads, the main species consumed during gala meals in Asia being Rhopilema
esculentum. Each year, the Japanese consume about 13 tons47. In China, which
breeds them in Korea, Thailand and Malaysia, jellyfish are also eaten dried,
especially in the form of kebabs. Their nutritional value is relatively limited
since they are composed of more than 98% water, but the remaining 2% contains
protein and carbohydrates48.
Overfishing or disappearance of predatory
species of jellyfish (tunas, herring, anchovies, turtles) 49, the disappearance
of competitors such as sardines, which increase the amount of food available,
"the destruction of seabed by trawlers Breeding, water warming, and
eutrophication of coastal environments "stimulate their proliferation, so
much so that researchers Philippe Cury and Daniel Pauly make the provocative
conjecture that" we will have to content ourselves with eating jellyfish!
"
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