Aurelia playlist link:-
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Lower invertebrate bsc 1st semester playlist:-
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In this video we will discuss about following topic:-
Reproduction and life history of Aurelia (Jellyfish)
Aurelia (Jellyfish) part - 6
a. Sex organs
b. Fertilization
c. Formation of planula larvae
d. Formation of scyphistoma
e. Formation of ephyrae( strobilation)
f. Ephyra larva
g. Metamorphosis
metagenesis in Aurelia (Jellyfish)
Reproduction and life history of Aurelia (Jellyfish)
Aurelia is dioecious i.e., the male and female sexes are separate but there is
no sexual dimorphism.
1. Sex organs
Testes and ovaries are similar in appearance. A medusa has 4 horseshoe-
shaped gonads radially lying on the floor of the stomach periphery, that is,
one in each gastric pouch.
The gonads are endodermal in origin.
They are reddish violet in color.
They are visible through the semitransparent jelly of the umbrella as frilled
organs with their concavities facing inwards.
On maturity, ova nad sperms break into the gastrovascular cavity and pass
out of the mouth with the outgoing water current. The ova and eggs are
lodged in the frill of oral arms.
2. Fertilization
Spermatozoa, swimming about in the water, reach the ova and fertilize them
either in the stomach of females or in the frills of oral arms. Thus,
fertilization is either internal or external.
3. Formation of planula larva
The frills of oral arms serve as temporary brooding members where
fertilized egg or zygote undergoes early development into a ciliated larval
stage called planula.
The zygote undergoes holoblastic and equal segmentation to produce a
solid ball-like morula.
Morula becomes a single-layered blastula soon by the accumulation of fluid
in its interior.
The two-layered gastrula develops by invagination, having outer ectoderm
and inner endoderm lining an enteron cavity, with its blastopore or gastral
mouth not completely closed. Thus, it differs from the gastrula of Hydrozoa
(e.g., Obelia) which develops by the process of delimitation and multipolar
regression of cells into blastocoel having no blastopore.
The embryo, now elongates, its outer cell becomes ciliated, blastopore
closes and the typical planula larva is formed. At this stage, masses of
planulae are visible as minute opaque patches on the oral arms of female
individuals.
4. Formation of scyphistoma
The ciliated planula eventually escapes and after a short free-swimming
existence attaches itself to a stone or seaweed by its aboral end.
The cilia are lost and a mouth opens at its free distal end where the
blastopore had closed.
The larva now becomes elongated and metamorphosed into a small
trumpet-shaped or Hydra-like polyp or hydratuba, about 5mm high.
The larva proximal part is narrowed into a stalk-like organ, attached to the
substratum by an adhesive basal disc.
Its tentacles bud out around the mouth where 4 tentacles are perradial,
subsequent 4 interradial, and then 8 adradial in position. Thus, 16 long and
slender tentacles are formed.
Its mouth becomes square in outline and its edges become elongated to
form a short manubrium.
The larva now looks like a trumpet-shaped polyp or Hydra and is called
hydratuba or young scyphistoma (Gr., skyphos, cup+ stoma, mouth).
The endoderm of its cavity is raised into 4 interradial longitudinal gastric
ridges or taenioles, characteristic of Scyphozoa, which divides the enteric
cavity into four perradial diverticula or pouches.
Simultaneously, the ectoderm between mouth and tentacles also becomes
invaginated as four interradial funnel-like depressions, known as septal
funnels or infundibula, which sink into four gastric ridges.
Scyphistoma feed and grows up to 12mm in height and may survive in this
stage for several months. Sometimes, it multiplies either by lateral budding
or by growing horizontal creeping stolons, which bud off fresh hydratubae.
These buds eventually separate from the parent, as in Hydra.
5. Formation of ephyrae( strobilation)
Scyphistoma undergoes a remarkable process of budding or transverse
fission of oral end in autumn and winter, called strobilation.
Distally, the body develops a series of ring-like transverse constrictions or
furrows which gradually deepens so that the organism resembles a pile of
minute saucers or disc, placed one above the other. At this stage,
scyphistoma with a segmented body is called strobila and each of the
segments is called ephyra larvae........etc..
Notes pdf link:- ( all part 6 full notes) :-
drive.google.com/file/d/17Z4ESg_4IFNoe-XClzoMLBaaEYtbREJ_/view?usp=drivesdk
Reference:-
microbenotes.com . microbenotes.com/aurelia-jellyfish/#reproduction-and-life-history-of-
aurelia-jellyfish
Thanks for watching video
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