Feeding behaviour of the hydromedusa Aequorea vitrina
Scientia Marina, 71(2): 395-404, 2007
Hans Ulrik Riisgård
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Video clip 1 (6.7
MB). – The hydromedusa Aequorea
stagnant water, where it remains stationary with its very long
(about 15 cm, or 4x bell diameter)
marginal tentacles hanging down motionless in the water, ready
for ambush capture of prey organisms that collide with the tentacles.
Video clip 2 (5.1
MB). – Aequorea
a brine shrimp (Artemia salina). When a freely swimming
Artemia touches an A. vitrina marginal tentacle it easily
sticks to the tentacle, which is immediately contracted and curled
up so that the adhered prey is tugged up to the umbrella margin.
As soon as the hydromedusa begins to curl up the tentacle with
an adhered Artemia, it simultaneously moves the part of the umbrella
margin where the tentacle is fastened towards the sub-umbrella
cavity. Soon after, the hydromedusa begins to move its mouth towards
this part of the umbrella margin. Thus, both the umbrella margin
and the mouth with the elongated mouth-lips move towards each other
until they come into contact so that the captured Artemia can be
transferred from the tentacle to the mouth-lips to be further transported
into the mouth.
Video clip 3 (3.6
MB). – Aequorea
vitrina capturing Artemia efficiently
and quickly. It takes about 20 s from the moment when the prey
organism encounters an extended marginal tentacle until it is transferred
to the mouth-lips. The initial hauling up of the adhering prey
is fast, but as the prey gets closer to the umbrella margin, the
velocity of the tentacle contraction decreases. The movement is
not continuous, and sometimes the tentacle stops contracting for
a while, or even relaxes somewhat if many preys are captured at
the same time.