Mnemiopsis is a carnivore that consumes zooplankton including crustaceans,[3] other comb jellies, and eggs and larvae of fish.

Indeed, much like the so-called Immortal jellyfish, Mnemiopsis leidyi can undergo reverse development, namely reverting into a previous life cycle stage.

[10] By 1989, the Black Sea population had reached the highest level, with some 400 specimens per m3 of water (>10 animals/cubic foot) in optimal conditions.

It caused a dramatic drop in fish populations, notably the commercially important anchovy Engraulis encrasicholus (known locally as hamsi, hamsiya, hamsa, etc.

[3] Biological control was tried with Beroe ovata, another comb jelly, with some degree of success; it appears as if a fairly stable predator-prey dynamic has been reached.

[3] One year later, the Baltic population of M. leidyi was found to have spread east to the Gotland Basin and the Bay of Puck.

[16] At least technically possible given the species' euryhaline habits is an alternative route of dispersal through continental Europe, being carried with ballast water in ships travelling from the Black Sea to the Rhine Estuary via the Rhine-Main-Danube Canal.

Both the nuclear and mitochondrial genomes of Mnemiopsis leidyi have been sequenced, providing insight into the evolutionary position of Ctenophora (comb jellies).

[17] [18] In the original 2013 paper reporting the nuclear genome sequence, phylogenetic analysis of the presence and absence of genes, introns, and amino acid alignments suggested that the comb jelly is the sister lineage to the rest of all animals.

The mitochondrial rRNA molecules possess little similarity with their homologs in other organisms and have highly reduced secondary structures.

MicroRNAs play a vital role in the regulation of gene expression in all non-ctenophore animals investigated thus far except for Trichoplax adhaerens, one of three known members of the phylum Placozoa.

[24] In Mnemiopsis leidyi, NOS is present both in adult tissues and differentially expressed in later embryonic stages suggesting the involvement of NO in developmental mechanisms.

Ctenophores also possess soluble guanylyl cyclases as potential NO receptors with weak but differential expression across tissues.

Combined, these data indicate that the canonical NO-cGMP signaling pathways existed in the common ancestor of animals and could be involved in the control of morphogenesis, cilia activities, feeding and different behaviors.