Abstract
Directional swimming in the box jellyfish Tripedalia cystophora (cubozoa, cnidaria) is controlled by the shape of the velarium, which is a thin muscular sheet that forms the opening of the bell. It was unclear how different patterns of visual stimulation control directional swimming and that is the focus of this study. Jellyfish were tethered inside a small experimental tank, where the four vertical walls formed light panels. All four panels were lit at the start of an experiment. The shape of the opening in the velarium was recorded in response to switching off different combinations of panels. We found that under the experimental conditions the opening in the velarium assumed three distinct shapes during a swim contraction. The opening was (1) centred or it was off-centred and pocketed out either towards (2) a rhopalium or (3) a pedalium. The shape of the opening in the velarium followed the direction of the stimulus as long as the stimulus contained directional information. When the stimulus contained no directional information, the percentage of centred pulses increased and the shape of the off-centred pulses had a random orientation. Removing one rhopalium did not change the directional response of the animals, however, the number of centred pulses increased. When three rhopalia were removed, the percentage of centred pulses increased even further and the animals lost their ability to respond to directional information.
Highlights
Box jellyfish are agile swimmers that use their elaborate visual system for orientation (Garm et al 2007b)
Directional swimming in the box jellyfish Tripedalia cystophora is controlled by the shape of the velarium, which is a thin muscular sheet that forms the opening of the bell
We showed that the Caribbean box jellyfish, Tripedalia cystophora, responds to the darkening of a quadrant of the equatorial visual world by creating an off-centred opening in the velarium and delaying contraction in the quadrant of the animal next to the dark sector (Petie et al 2011)
Summary
Box jellyfish are agile swimmers that use their elaborate visual system for orientation (Garm et al 2007b). The velarium is a thin muscular sheet (Gladfelter 1973; Satterlie et al 2005) that constricts the outflow opening of the bell during swim contractions. It is unclear how visual stimulation controls the shape of the velarium. We showed that the Caribbean box jellyfish, Tripedalia cystophora, responds to the darkening of a quadrant of the equatorial visual world by creating an off-centred opening in the velarium and delaying contraction in the quadrant of the animal next to the dark sector (Petie et al 2011). We investigate the shape of the velarium in response to different patterns of light and dark quadrants
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