Explore to Koh's Science World ( Blog Sains): Jellyfish (ubur-ubur)

Tuesday, 28 April 2015

Jellyfish (ubur-ubur)

How do jellyfish reproduce?

Eggs and sperm are released by adult jellyfish--sometimes at incredible rates.
A jellyfish egg unites with a jellyfish sperm to produce a larva.

Each larva attaches to a hard surface, such as a rock or an artificial structure like a drilling rig, at the ocean bottom.

The larva lives as a stationary polyp at the ocean bottom.

Once conditions become favorable, each polyp elongates and then buds off and releases many young jellyfish.

A single polyp may thereby, by itself, reproduce large numbers of jellyfish.

What's more, individual polyps probably don't churn out young jellyfish in isolation.

Rather, fields of polyps probably simultaneously transform into veritable jellyfish factories, mass producing tens of thousands of jellyfish at a time.

Swarms of young jellyfish may thereby quickly form when their survival prospects are best.

Each young jellyfish rapidly develops into an adult jellyfish, and the cycle repeats.

(source: http://www.nsf.gov/news/mmg/mmg_disp.jsp?med_id=65102&from=mmg )

Jelly fish can reproduce two ways, both sexually and asexually. In asexual reproduction they bascially split or produce a bud which separates and swims off. When they reproduce sexually a male squirts its sperm into the sea which swim into the mouth of the female and fertilise her eggs. The egg then grows into a larva which swims away from its mother and develops into a jelly fish. They actually have two different stages in their life cycles, one in which they swim around the sea as we know them and another in which they attach to rocks unable to move. This is called a polyp and is like an upside down jelly fish with the tentacles waving up above them grabbing food, like a squidgy coral. The polyp stage usually comes before the swimming stage.

Different jellyfish reproduce in different ways. The moon jellyfish has a four stage lifecycle. The adult female produces eggs which she holds in her mouth and fertilises them with the males sperm before releasing the larvae into the water. The larvae attach to a hard surface to form polyps – similar to sea anemones – which may themselves reproduce by budding off clones of themselves. At maturity these polyps divide into sections, each of which develops tentacles to form the adult medusa.

水母雌雄異體，有生殖腺在近胃囊處。成熟的精子流入雌水母體內受精。受精卵發育成幼蟲離開母體，在水裏游動一會兒後，沉下海底形成幼體，後變成橫裂體，橫裂體分裂成多個碟狀幼體，再發育成水母成體。