The Wouters organ presence and its detecting in Heterocypris

Abstract

In 2008, Robin Smith and Renate Matzke-Karasz presented a large survey on the morphology and presence of the Wouters organ within Cypridoidea. The new organ was present in the genera Hemicypris, and Homocypris, but not detected in Cyprinotus or the cosmopolitan genus Heterocypris of the subfamily Cyprinotinae. With the aim to explore the possibilities to spot this tiny structure in Heterocypris, ten females from ten different species occurring in Europe were examined. The exception was Heterocypris exigua, where 9 specimens were inspected. Next to this, the species investigated were Heterocypris barbara, H. bosniaca, H. erikae, H. gevgelica, H. incongruens, H. reptans, H. rotundata, H. salina and H. vitrea. To detect and measure the Wouters organ, both left and right antennulae were observed and photographed using a Zeiss Axioimager microscope with a magnification of 500 times. The Rome organ was also measured, as well as the distance of the Wouters organ from the first setae on the antennulae, to determine its position. The presence of the vase-shaped Wouters organ is noted in all analyzed species at 64.60 μm mean distance from the first seta. The mean length of this sensory organ was 5.93 μm and the success of its detection was 63% in total. The Rome organ was successfully detected in almost 90% of the examined antennules, with the mean length of 10.27 μm. It is interesting that the Wouters organ is found in one more species with short natatory setae on the second antenna, namely Heterocypris reptans. These results also emphasize that the Wouters organ is probably present in many species but it is just overlooked. The success in finding it is related to conservation of the sample, dissection techniques, slide preparation procedure, stronger magnification and looking for it in a larger number of prepared specimens.