I chose to experiment with the effects of salinity changes on the polychaete, Nereis succinea. Along with the other members of the group, Patty and Jeremy, I was curious to see whether the worms would engage in adaptive behavior when placed in a tank of water of foreign salinity, or whether they would simply continue changing osmotically until they reached equilibrium with the environment.
The first step in our experiment was to simply observe the worms and get a “feel” for the ways in which they act. We did this on Wednesday, May 7, 1997 from 9:30am to 10:30am. Also on this day we learned how to mix and measure salinity, practiced weighing the worms, and deciding our exact schedule as far as when we would come in and for how long, etc.
From what I observed, the polychaete is a salt-water worm that has adapted to live in estuaries. We kept the control tank at 20 parts per thousand to 24 parts per thousand, and the worms seemed very content and healthy at that level. The worms on which we experimented ranged in size from approximately four inches to approximately six inches. They weighed from 1.8 grams to 4.6 grams at the beginning of the experiment. They have a pinkish, almost salmon color to them, and on two opposite sides, they have these crimson hairs lined up in a row, stretching the entire length of their bodies (the hairs are less than an eighth of an inch long). If we were to call the two lines of hair “east and west”, then on the “north and south” sides, there were dark lines that also stretched the entire length of their bodies. These were their primary blood vessels, and though we tried to locate the pulse that is supposed to conspicuously travel up and down this vessel, we were not able to l!
ocate it, except once on one worm for less than 30 seconds. Also I often was not able to tell the difference between the head and the tail.
Their actions were very basic. They seemed to like to stay still for the most part, hiding underneath the little bit of seaweed we put in the tank. We also put a glass tube at the bottom of the tank, thinking that they might try to crawl in there for safety, but we never saw them in there. Basically, they remained very still, except for certain instances in which they seemed to start flailing uncontrollably. They would start swimming around in circles or in figure eights or in some other odd pattern. It was actually quite hilarious to watch. I was not quite sure why they did that, but I guessed that they were looking for something. I later found out that that was true, that they were looking for some sort of protection (like the seaweed).
I made another very shocking and interesting discovery the first time I took a worm out to weigh it. I took it out with a net and put it on a paper towel, and as I was walking to the scale, this “thing” jumped out at me from inside the worm (I literally almost dropped the poor guy!). The only way I can really explain it is if you take a sock and turn it inside-out. The worm basically extended its body by “unfolding” this unknown thing from inside. After the initial scare, I later come to realize that this is called the “reversible probascis” or something to that effect. I learned that the worm uses it to catch small fish when it is hiding in some seaweed. I also observed it later and found little teeth on the end of the probascis. That basically sums up the activity that I noticed.
After observing the worms, I formulated the hypothesis that, when facing a change in salinity, the worms would adapt osmotically to the environment and their volumes would change, but they would not make any efforts to re-adapt back to their original volumes. The reasons I formulated this hypothesis were quite frankly less than scientifically stable. When I looked at the worms, I saw a very basic physiology, and I suppose I figured that a basic physiology like that would be less