Notes:-
Aurelia (A Jellyfish)
Table of Contents (part- 1st)
Systematic Position
Habit and Habitat of Aurelia (Jellyfish)
External morphology of Aurelia (Jellyfish)
1. Shape and size
2. Colouration
3. Manubrium, mouth, and oral arms
4. Subgenital pits
5. Gonads
6. Lappets and tentaculocysts
7. Marginal tentacles
8. Velarium
Systematic Position -
Phylum: Coelenterata
Class: Scyphozoa
Order: Semaeostomae
Family: Ulmaridae
Genus: Aurelia
Species: aurita
Habit and Habitat of Aurelia (Jellyfish)
It is cosmopolitan jellyfish occurring in warm and temperate seas ranging in
temperature from 6-19ºc all over the world.
It lives in coastal waters singly or in large shoals.
It can live in waters with a salt content as low as 0.6%. Salt content and
water temperature affect the shape, size, and reproductive strategies.
They thrive best in waters with temperatures are above 17.5°C and salinity
greater than 38.0%, largest.
It ranges in depth between the epipelagic zone and the mesopelagic zone
(200 to 1,000 m).
It is found either floating with water currents or waves or swimming feebly
by the contraction movements of its bell.
It is carnivorous, feeds on small organisms with the help of its long oral
arms.
It responds to various stimuli and is most active in diffuse light.
External morphology of Aurelia (Jellyfish)
1. Shape and size
It is a large version of the medusa of Obelia.
It looks like a soft bell or umbrella-shaped body with 4 red or purple
horseshoe-shaped gonads on its upper surface and 4 long and narrow oral
lobes hanging downwards from the lower surface.
Its circular body measures about 90mm in diameter and presents a
convex aboral or exumbrellar surface and a concave oral or subumbrellar
surface.
2. Colouration
Its body is perfectly transparent and bluish-white in color.
The reddish or pinkish horseshoe-shaped gonads are clearly visible from
the body surface.
3. Manubrium, mouth, and oral arms
A very short and inconspicuous manubrium is present in the
center of the subumbrellar surface.
At its free distal end is a square mouth, from each corner of
which hangs down a long, tapering much-frilled and delicate
process, the oral arm.
Each of the four oral arms has a ventral ciliated groove leading
into the mouth and its edges are armed with nematocysts.
The radii, along which angles of the mouth and oral arms lie, are
referred to as perradii.
Midway between two adjacent perradii is an interradius, and
between each perradius and its adjacent interradius, on either
side, is adradius.
4. Subgenital pits
On each interradius, a little distance from the mouth, the sub-
umbrellar surface bears a circular aperture. It leads into a small
shallow cavity, the subgenital pit, lying immediately between a
gonad and of uncertain function.
5. Gonads
A horseshoe-shaped and frilled gonad are present just above each
subgenital pit within the umbrella.
It is red or purple in color.
Free arms of all the four gonads are directed towards the center of
the umbrella. There is no connection between gonads and
subgenital pits.
6.Lappets and tentaculocysts
The circular margin of the umbrella or bell is broken into 8 lobes by 8
indentations or notches, 4 of which are perradial and the other 4 interradial.
In each notch, there are two delicate leaf-like processes, called the marginal
lappets.
Between lappets lies small sensory organs, the tentaculocyst or rhopalium.
7. Marginal tentacles
Between notches or rhopalia, the free edge of the umbrella is beset closely
with a row of numerous small, delicate and hollow threads or marginal
tentacles.
The tentacles bear a number of stinging cells or nematocysts.
8. Velarium
The margin of the subumbrellar surface, bearing lappets and tentacles,
forms a thin and flexible flap, called velarium or pseudovelum.
It differs from the true velum of Obelia in having gastrodermal canals
running into it. Such medusa with a pseudovelum(e.g., Aurelia) is called
acraspedote medusa, while a medusa with atrue velum (e.g.,Obelia) is
called craspedote medusa.
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