LIFE HISTORY OF THE CANNONBALL JELLYFISH,STOMOLOPHUS MELEAGRISL. AGASSIZ, 1860 (SCYPHOZOA, RHIZOSTOMIDA)

Stages in the life history of the scyphozoan Stomolophus meleagris from the planula to the newly liberated ephyra were raised in the laboratory and are described for the first time. After swimming actively for 2-5 days, the ciliated planula larvae settled and scyphistoma morphogenesis occurred. Fully developed scyphistomae were cone-shaped and bore a whorl of about 16 tentacles around a dome-or knob-shaped proboscis. Podocyst formation was the only observed method of asexual reproduction in cultures of scyphistomae maintained for one month. Strobilation began as soon as nine days after scyphistoma morphogenesis and occurred in scyphistomae with as few as eight tentacles. The strobilation process, completed in about 3.5 days at 25°C, was not accompanied by any noteworthy color changes. Most strobilae produced two ephyrae each, although the number varied from one to three. Some scyphistomae began to strobilate a second time within a week after completion of an initial round of strobilation. Newly liberated ephyrae possessed a normal complement of eight lappet pairs and eight rhopalia. They were morphologically similar to, yet distinguishable from, ephyrae of the related species Rhopilema verrilli. None of the examined stages of S. meleagris contained algal symbionts.