Local Species: Mnemiopsis jellies

This post is part of an occasional series on local marine species compiled and photographed by New England Aquarium aquarist Peter Gawne. When he's not diving locally for these posts or researching coral reefs in Belize, Peter takes care of the touch tank's sharks and rays and the jellies exhibit.

This post is the first of a two-part series about mnemiopsis jellies.

Leidy’s comb jelly (Mnemiopsis leidyi)

Leidy’s comb jellies, like all ctenophores, use rows of cilia for propulsion.  These rows of cilia resemble eyelashes or combs.

Leidy’s comb jelly belongs to the phylum Ctenophora, and is native to the western Atlantic Ocean.

While Leidy’s comb jellies resemble cnidarian jellies, such as moon jellies and Atlantic sea nettles, they are classified as ctenophores and are actually not even closely related. The most distinctive feature of ctenophores is the comb-like arrangement of rows of cilia used for swimming. These rows of cilia diffract light, resulting in the appearance of rippling bands across their bodies. While ctenophores are capable of bioluminescence, it should be noted that this phenomenon is merely the result of light scattering off the cilia, and is not light generated by the animal itself. Leidy’s comb jellies are lobed ctenophores, meaning that they possess muscular cuplike extensions of the body on both sides of the mouth. Minute tentacles line the inner surfaces of the lobes.

Leidy’s comb jellies are carnivorous and complex predators with a variety of different structures and behavioral patterns, which contribute to their feeding success. They use cilia to create a low-velocity flow, referred to as the auricular flow field, in which small prey species are entrained.  Once captured in this flow, the prey are carried past the oral lobes and onto the oral tentacles. Essentially, the comb jelly is filter-feeding small particles from the water column as they are impelled past its feeding surfaces.

Interestingly, Leidy’s comb jelly has evolved an alternative mechanism for the capture of larger, more motile prey.  Larger prey are ambushed by the jelly’s outstretched oral lobes.  Prey that are big and strong enough to swim against the auricular flow field are self-propelled against adhesive cells, called colloblasts, lining the oral arms.

To capture its prey, Leidy’s comb jellies utilize the colloblast cells located in its tentacles. Much like the nematocysts of cnidarians, these cells contain a coiled filament which uncoils when triggered and impacts the prey. However, the similarities end here – unlike nematocysts, colloblast cells are not venomous, but rather contain granules. Upon contact with the prey, these granules rupture, releasing an adhesive substance which entraps the prey. Unable to escape, prey are transported to ciliated oral grooves, and transferred to the mouth. Colloblast cells are harmless to humans.

The most important consequence of the various feeding mechanisms of Leidy comb jellies is the wide variety of prey removed from marine plankton food chains. Leidy’s comb jellies are able to indiscriminately capture a wide spectrum of planktonic prey, both large and small.

Tune in for Part Two of this series about comb jellies to learn how these brainless blobs can attack an ecosystem unequipped with natural predators with ruthless precision.

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