Mnemiopsis leidyi

Mnemiopsis leidyi
Sea walnut, Comb jelly



It is a species without stinging cells (cnidocytes), therefore it is completely harmless for the humans.


Mnemiopsis leidyi has a gelatinous consistency, however it does not belong to the group of Cnidarians, it is a ctenophore and belongs to the phylum Ctenophora.

It has an oval, translucent body that can reach up to 12 cm in length. It lacks tentacles and presents eight rows of ciliated combs that run its body vertically, from the oral to the aboral pole, and produce blue-green iridescence. This species does not swim with the pulsations of its body like jellyfish, but is propelled thanks to the beating of its eight rows of cilia. It presents two lobes in its oral end, whose length and amplitude vary according to the zone where it develops.


This invasive species was recorded for the first time on the Catalan coast in 2009. Currently, its presence is intermittent in some parts of Catalonia, but on the south coast, especially on the Ebro Delta, there is an established population that it is under rigorous monitoring in order to estimate the possible effects of its invasion in that zone.

Distribution and Habitat

This species is native to estuaries and coastal areas of the western Atlantic Ocean, distributed along the coast of the United States to Argentina. In the early 1980s, it reached the Black Sea transported in the ballast water of American ships, and in the last three decades has expanded to almost all eurasian waters, including the Mediterranean basin. The records of the western Mediterranean appeared for the first time in 2006, and in 2009 was recorded for the first time in catalan waters.