Shape Changers
 In the oceans of the world, golf-ball-sized blobs glide through the water gobbling up tiny zooplankton. Although native to the eastern coast of the United States, Mnemiopsis leidyi ctenophores — jellyfish-like creatures — have invaded the Baltic and Aegean seas, carried in the ballast water ships use for stabilization when their cargo holds are empty. With no natural enemies in their new homes, the ctenophores have flourished to the point that they have pushed out other native fish that also feed on the zooplankton, leading worried ecologists and fishermen to search for a way to control the burgeoning population.
One possibility is a mysterious anemone — Edwardsiella lineata — one that scientists have misnamed and misunderstood for decades. For the past year, biology graduate students Adam Reitzel and James Sullivan have studied this bizarre creature, tracing its life history through its weird twists and turns.
Edwardsiella lineata begins its life in the guts of the ctenophores. Essentially a parasitic worm that looks like a mouth with a sack attached, it feeds off of the ctenophore. After growing up to 1.5 cm, it leaves the ctenophore, moving on to the next stage — a tiny 1–2 mm-long football-shaped larva with tiny hair-like cilia that whip around, propelling it through the water.
One to four weeks later it morphs into a star-shaped critter with eight tiny tentacles. In this stage, the organism’s body tissue is undifferentiated — it has the potential to become a variety of different tissues, much like a stem cell. These tissues slowly grow into the adult form — a classic anemone with a tube-like body sprouting a tuft of arms on top.
Sullivan and Reitzel collected more than 200 of these animals in their parasitic worm form by capturing ctenophores in the waters off Woods Hole. In their lab the students observed something no other scientist had seen before —the anemone’s complete life cycle. Previously, scientists had believed that the different life phases of the anemone were completely different animals.
Because of their parasitic nature in the worm-like stage, some scientists have proposed using the anemone to biologically control the rampant ctenophore populations in European seas, but both Reitzel and Sullivan are cautious. They have noted that some of the anemones reproduce asexually in both the parasitic and adult form, while others reproduce sexually. The cause of this remains a mystery. They assert that releasing the anemones into new environments before understanding how they reproduce invites potential catastrophe.
Sullivan and Reitzel may already be the leading experts on this little-known anemone, but they intend to continue studying them. The excitement of studying animals no one else knows about fuels his interest, says Reitzel.
For more information, see: http://www.bu.edu/cecb/info/update2005.pdf
— Elana Hayasaka
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