The comb jelly (Mnemiopsis leidyi), sometimes called the “sea walnut,” is a species of tentaculate ctenophores (stingless jellyfish). Ctenophores are distinguished from all other animals by possession of sticky cells called colloblasts and their eight rows of cilia. They are the largest animal known to use cilia for locomotion.
Unlike cnidarian jellyfish, Mnemiopsis catch prey using their colloblasts—sticky glue-like adhesive cells on their tentacles—rather than stinging cells. Their prey consists of zooplankton including crustaceans, other jellies, eggs, and fish larvae. There is no permanent connection between the gut of the comb jelly and the rear of the body. It has a “Transient anus,” which only appears during defecation. Comb jellies are native to the western Atlantic Ocean, but have become notorious invasive species in the Black, Caspian, Mediterranean, and North Seas of Europe and Western Asia. They were likely transported in the ballast water of ships.
Since MBL opened its doors in 1888, scientists and students have been studying the interesting and unique biology of the ctenophore Mnemiopsis leidyi. During the summer months Mnemiopsis leidyi can be found in Eel Pond, at the NOAA jetty, and in other nearby harbors. Experimental embryologists at MBL have a long history of using Mnemiopsis for cell lineage analyses, facilitated by the rapid and synchronous development of their optically transparent embryos.
MBL researchers have characterized aspects of Mnemiopsis biomechanics that may underly their invasive success as well as how ctenophores use their namesake giant cilia for locomotion. Insights from sequencing the whole genome of Mnemiopsis leidyi has served to highlight the early branching relationship of ctenophores relative to other animal phyla and driven a resurgence of interest in ctenophore biology.