Scientia Marina
Supplementary material

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 vitrina in 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 vitrina capturing 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.