Popular science helps to discover the abundance of this jellyfish
(PHYSorg.com Biology)

When the Rhizostoma luteum jellyfish was discovered at the beginning of the 19th century in the waters of the Strait of Gibraltar, only nine specimens were identified. For years, it was so inconspicuous that in the 20th century, it failed to turn up for six decades. A team of scientists with the help of a citizen initiative has now confirmed that it is not really as difficult to find as previously believed.