The analysis of the concept of “species” in relation to the sibling species and morphologically close species as well as the problems of their distinction and recognition. Three groups of factors influencing the description and recognition of the biota cryptic diversity (BCD) are analyzed, including eidological, epistemological and cognitive aspects. The first group of factors (eidological) is the most objective, and our knowledge is developed towards the increasing approximation to the actual existing biodiversity. Meanwhile, there is a more widely accepted recognition of the fact that, in addition to species diversity, there is also a diversity of levels of species-group taxa differentiation. Such development is the essence of epistemological component of the BCD description and recognition. However, the investigators’ possibilities are extremely different due to their individual characteristics and aptitudes, especially due to the polymorphism in resolution of sensor systems for distinguishing objects or some features thereof, including through natural blindness (in the broad sense) or, on the contrary, due to extraordinary abilities. Important role in the vision of species diversity in some groups, levels of taxa differentiation and their distinctions plays such ex-sensorial factors as knowledge, investigator’s school, prevailing concepts and paradigms, understanding of taxa variation and entireness. Examples of both diversity of levels of close forms differentiation, and viewpoints on their status are given, as well as examples of different estimation of diversity in the same groups given by different investigators. Development of eidology resulted in the formation of one more aspect of diversity, the species conception diversity. It assures the non-universality of «species» idea, and, therefore, its subjectivity. Species as a concept, as well as a manifestation of biodiversity is unequivocal concept only in the analysis of biotic communities, outside of space and time.