Invertebrate Department

Excretory organs

The excretory system in L. maerski consists of two pairs of protonephridia. This kind of excretory organs is very common in small animals without circulatory system or body cavity. The protonephridia are located laterally in the most anterior pseudosegment in the thorax and in the anterior part of the abdomen. 

A protonephridium is a tube-like structure consisting of one or more terminal cells, canal cells and a nephridiopore. The terminal cells are located in the bottom of the protonephridium. Each cell has one or several cilia and when they beat inside the protonephridial tube they create an outward going current and hence a partial vacuum in the bottom of the tube. Because of this partial vacuum waste fluids from the inside out the animal are pulled through small perforations in the terminal cells and into the protonephridium. The perforations in the terminal cell are so large that small molecules can pass whereas larger proteins are retained in the animal. From the bottom of the protonephridium the waste fluid is led through the tube, formed by the canal cells, and exits the animal from a small opening formed by the  nephridiopore.



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Last update: 30 maj 2007


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