Uiblein, F., Ott, J., Stachowitsch, M. (Eds): Deep-sea and extreme shallow-water habitats: affinities and adaptations. - Biosystematics and Ecology Series 11:123-143. The darkness syndrome in subsurface-shallow and deep-sea dwelling Ostracoda (Crustacea) D. L. DANIELOPOL, A. BALTANÄS & G. BONADUCE Abstract: Animals that permanently live either within subsurface habitats in shallow marine environments of Consolidated and/or loosely packed sediments or on the bottom of the deep sea commonly display a complex of morphological and biological traits that is here termed the darkness syndrome. Classic examples are regressed ocular structures and body pigments, combined with the compensatory development of extra-optic sensorial traits. It is largely accepted that animals which adapt to the aphotic subsurface and deep-sea habitats become prisoners of their constraining environment. The Austrian zoologist Th. FUCHS, using examples from the Atlantic Ocean, was the first (1894) to propose a deep-sea origin for the shallow marine cave fauna. Modem biological literature offers additional arguments for this hypothesis. Here, evidence is presented for an alternative and/or additional scenario: shelf-dwelling animals, which are not strongly specialized for life in the photic environment, easily colonize deep-sea and/or shallow subsurface habitats. Examples from two major groups of ostracods, Podocopida and Halocyprida, are used in support of this latter evolutionary model. Introduction The high biological richness of our planet Earth is partly due to photosyn thesizing organisms, which efficiently capture and use solar energy. Much of the scientific effort in the past was dedicated to describing diversity of life, which evolved at the surface of the planet in well-illuminated habitats. Since antiquity, however, man has recognised that life also exists in darkness. The quest for answers as to why organisms have chosen to live in environments deprived of light and how such organisms adapted to living conditions perceived by man as very constraining, represents, what G. HOLTON (1986) would call a persistent cultural thema. It is now fully realised that life in darkness is widespread. Both Earth’s subsurface waters and large parts (more than two thirds) of the oceans are devoid of light. HUTCHINSON (1965) coined the term allobiosphere for the large domain where life exists without the participation of solar energy and the primary photosynthesizing producers. The aquatic allobiosphere, in addition to the two characteristics mentioned above (extraordinary wide distribution and lack of light), was generally 123 ©Akademie d. Wissenschaften Wien; download unter www.biologiezentrum.at