Dear Okan, I agree, it is an important point to discuss on it, and there may be a lot of different parameters to generate a new species, all the best,

As a Paleontologist working with ostracods, I set my personal number as 10. It gives you plenty of room to evaluate if a group of specimens is morphologically different from another one.

I think,, 10 can be considered. However, here is my approach for the numbers of individuals. First, this view can be used for some crustaceans (if not all others). Second, it also depends on type of species reproduction.

1) If you have a parthenogenetic species (no males), you may need to dissect at least 3-5 adult individuals to make things clearly identified (e.g., drawings the parts clearly). After that, you need at least 1-3 individuals for SEM photographings (this is kind of a common practice to see all details in carapace and soft body parts). Later, you need to (mostly required) deliver 3-5 individuals to the museums, and keep some with your own collections. This totally makes about 10-15 individuals.

2) If you have a bisexual species (with males), you may need to double this number.

3) Remember that we are talking about adults. In same cases, juveniles can also be dissected and/or needed for identifications.

It's really a matter of debate. But, it depend of several parameters, so you have to specify in which group micro or macro. first. For micropaleontology field, is not only the number of specimen that count in order to describe new taxa ! a lot of other parameters, mainly the morphometric and morphological one, have to be definitely considered, but this issue cannot be established if the preservation degree of the studied material is not good. So, from my experience, a huge amount of species that have been created on the basis of sometimes 1 specimens, or badly preserved materials, as it is the case in ostracods, forams, etc. However, I appreciate the new way (rules) applied by some micropaleontologistes in describing new species, as in case of the charophyte group, where specialists usually use at least 50 specimens, to overcome the problem of intrapopulationnal and ecophenotypic variation.