Sea walnut or Comb jelly : Mnemiopis leidyi

Kingdom : Animalia
   Phylum : Ctenophora
          Class : Tentaculata
               Order : Lobata
                    Family : 
                         Genus : Mnemiopis
                              Species : leidyi 


The comb jellies, or sea walnuts, are characterized by having a milky, transparent, iridescent body that is oval to pear shaped and somewhat flattened.

They are 10 cm long and 5 cm wide with eight rows of comb plates.


Sea walnuts are predaceous, bi-radially symmetrical animals with two oral lobes extending from a large mouth that is surrounded by four ciliated flaps.

Like the other comb jellies they have glue cells or colloblasts on their tentacles to catch their prey.

Introduced species:

This comb jelly is found naturally in the shallow waters of the western Atlantic ocean, from Cape Cod to Argentina. In the early 1980s, M.leidyi was accidentally introduced to the Black Sea, probably in ballast water from US cargo ships.

It is a self-fertilizing hermaphrodite, preadapted to rapid colonization. Due to the absence of predators in this new environment it rapidly reached very high abundance. In addition M. leidyi has an ability to regenerate from fragments larger than one quarter of an individual.

Since its accidental introduction, the fishering industry in the Black sea has declined catastrophically, with annual losses of over $250 million.

Recently this tiny predator has moved into the Caspian sea. See: