Life History & Behaviour
Hydrozoans typically have a complex life cycle which may include a polyp stage, a medusa stage or both (Ruppert 1994). When both stages are present, the polyp stage remains asexual and the medusa stage is sexual. Leptothecata usually form colonial polyps which grow rapidly on rocks and shells. Below is an image depicting the typical life cycle of a Leptothecata.
Leptothecata life cycle adapted from Ruppert, Fox & Barnes 2004.
While currents affect most of the dispersal of the medusa, a ring of muscles can contract in a rhythmic pattern to give them some movement using jet propulsion. The video below shows this.
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