To test the reversibility of this nighttime quiescent state, we introduced a food stimulus at night, which transiently increased activity to daytime levels ( Figure S3E). These results demonstrate that Cassiopea have a quiescent state during the night. To ensure that day feeding does not cause the day-night behavioral difference, we tracked the activity of 16 jellyfish over three consecutive days and nights without feeding and observed results consistent with those including feeding ( Figures 2F and 2G Figure S3D). Pulsing activity peaked upon feeding, occurring on the fourth hour of each day ( Figures 2C and 2D). Jellyfish activity decreased throughout the first 3–6 hr of the night, with the lowest activity occurring 6–12 hr after the day-to-night transition. Despite variations in basal activity, the relative change from day to night was similar between jellyfish ( Figure 2D). To determine whether fast- and slow-pulsing jellyfish change their activity to a similar degree, we normalized activity of individual jellyfish by their mean day activity. Although individual jellyfish showed different basal activity levels ( Figure 2C), all showed a large decrease in mean activity (∼32%) at night (781 ± 199 pulses/20 min, mean ± SD) compared to the day (1,155 ± 315 pulses/20 min, mean ± SD Figures 2C and 2E). We define “activity” as the total number of pulses in the first 20 min of each hour. To quantify this difference in pulsing frequency, we tracked the pulsing behavior of 23 jellyfish over six consecutive days and nights ( Figure 2C). We observed that Cassiopea pulse less at night than during the day ( Figure 2 Data S1). Together, these results indicate that Cassiopea has a sleep-like state, supporting the hypothesis that sleep arose early in the metazoan lineage, prior to the emergence of a centralized nervous system. When deprived of nighttime quiescence, Cassiopea exhibited decreased activity and reduced responsiveness to a sensory stimulus during the subsequent day, consistent with homeostatic regulation of the quiescent state. Monitoring of Cassiopea pulsing activity for consecutive days and nights revealed behavioral quiescence at night that is rapidly reversible, as well as a delayed response to stimulation in the quiescent state.

displays a quantifiable pulsing behavior, allowing us to perform long-term behavioral tracking. Within Cnidaria, the upside-down jellyfish Cassiopea spp. Introduced marine species of Hawaii Guidebook.] exhibit periods of quiescence, a pre-requisite for sleep-like states, prompting us to ask whether sleep is present in Cnidaria. Alien invasive invertebrates- Upside down jellyfish. A guidebook of introduced marine species in Hawaii. Big Island: Waikoloa fish ponds (Eldredge & Smith, 2001).Molokai: Kaunakakai (Eldredge & Smith, 2001).O‘ahu: Kāne‘ohe Bay, Ala Wai Canal, Honolulu Harbor (Eldredge & Smith, 2001).Spread by hull fouling or in the ballast water of ships (EOR, 2015).Came from the Philippines to Pearl Harbor between 19 (Eldredge & Smith, 2001).Ecological impacts have not been studied (Eldredge & Smith, 2001).Have a mild sting (Eldredge and Smith, 2001).Found in calm, shallow water such as lagoons and intertidal flats (EOR, 2015).

Lies upside down on sandy bottoms (EOR, 2015).Often mistaken for sea anemones (Eldredge & Smith, 2001).Can grow up to 30 centimeters in diameter (Bishop Museum, 2001).Yellow with white and pale spots (EOR, 2015).

Cassiopeia jellyfish