• Musio C. and S. Santillo (2012) Non-Visual Photosensitivity and circadian vision. In: CRC Handbookof Organic Photochemistry and Photobiology, 3rd ed., A. Griesbeck, F. Ghetti & M. Oelgemoeller, Print ISBN: 978-1-4398-9933-5 eBook ISBN: 978-1-4665-6125-0 DOI 10.1201/b12252-51
• Musio C. and S. Santillo (2009) Non-Visual Photoreception in Invertebrates. In: Photobiological Sciences Online, (KC Smith, ed.) American Society for Photobiology, http://www.photobiosci.info/ (Editorial Advisory Board: Thomas M. Brennan, Dickinson College, Carlisle, PA; John Lee, University of Georgia, Athens, GA; Francesco Lenci, Istituto Biofisica CNR, Pisa, Italy; James Shinkle, Trinity University, San Antonio, TX), 1-32.
• Cristino L., V. Guglielmotti, A, Cotugno, C. Musio and S. Santillo (2008) Nitric oxide signaling pathways at neural level in invertebrates: functional implications in cnidarians, Brain Research, 1225:17-25. ISSN: 0006-8993; DOI: 10.1016/j.brainres.2008.04.056
  
• Cristino, L., Guglielmotti, V., Musio, C., Santillo, S., 2007. Diffuse nerve net of Hydra revealed by NADPH- diaphorase histochemical labelling. Lect. Notes in Computer Sciences 4729, 11-20. ISSN: 0302-9743; ISBN: 978-3-540-75554-8;
• Santillo S., P. Orlando, L. De Petrocellis, L. Cristino, V. Guglielmotti & C. Musio (2006) Evolving visual pigments: Hints from the opsin-based proteins in a phylogenetically old eyeless metazoan, BioSystems, 86:3-17. ISSN: 0303-2647; DOI: 10.1016/j.biosystems.2006.03.008
• Santillo S., P. Orlando, L. De Petrocellis, L. Cristino, V. Guglielmotti, & C. Musio (2005) Molecular and functional diversity of visual pigments: Clues from the photosensitive opsin-like proteins of the animal model Hydra. Lect. Notes in Computer Sciences, 3704: 225-234. ISSN: 0302-9743; ISBN: 3-540-29282-9; WOS: 000233332300023
• Taddei-Ferretti C., C. Musio, S. Santillo and A. Cotugno (2004) “The photobiology of Hydra's periodic activity", In: Hydrobiologia, 530/531:129-134. ISSN: 0018-8158; DOI: 10.1007/s10750-004-2680-6; : 000226416700017;
• Musio C., S. Santillo, C. Taddei-Ferretti, L.J. Robles, R. Vismara, L. Barsanti and P. Gualtieri (2001) First identification and localization of a visual pigment in Hydra (Cnidaria, Hydrazoa), J. Comp. Physiol. A, (JOURNAL OF COMPARATIVE PHYSIOLOGY A-NEUROETHOLOGY SENSORY NEURAL AND BEHAVIORAL PHYSIOLOGY) 187(1):79-81. Feb2001 ISSN: 0340-7594; WOS: 000167635200009; DOI: 10.1007/s003590100180
  
• Taddei-Ferretti C., C. Musio, S. Santillo & A. Cotugno (2000) «The problem of Hydra photoresponse», in: Biodiversity and Environment, AK. Aditya and P. Haldar, eds, Delhi, Daya Publishing House, pp. 117-122. ISBN: 8170352266 / 9788170352266
• Musio C., S. Santillo, M. Nobile, A. Cotugno and C. Taddei-Ferretti (1998) «Compound and cellular bioelectrical activity and the dermal photosensivity of Hydra», in: From Structure to information in Sensory Systems, C. Taddei-Ferretti and C. Musio, eds, Singapore, London: World Scientific, Vol. 5, pp. 482-486. ISBN/ISSN: 981-02-3598-4
• Santillo S., C. Taddei-Ferretti and M. Nobile (1997) Resting Potentials recorded in the whole-cell configuration from epithelial cells of Hydra vulgaris, Italian Journal of Zoology Italian Journal of Zoology 64:7-11. ISSN: 1125-0003; WOS: A1997WU36500002;
• Taddei-Ferretti C., C. Musio, A. Cotugno & S. Santillo (1994) Non ionizing radiation and temperature effects on Hydra motility, Physica medica 10:88-89. ISSN: 1120-1797
• Taddei-Ferretti C., C. Musio, S. Santillo & A. Cotugno (1997) «Combined light and temperature effects on Hydra periodic behaviour», in: Coelenterate Biology, J.C. den Hartog, ed., National Natuurhistorisch Museum, Leiden, The Netherlands, pp. 473-482.
• Taddei-Ferretti C., C. Musio, S. Santillo & A. Cotugno (1997) «Hydra photosensitivity» in: Biophysics of Photoreception: Molecular and Phototransductive Events, C. Taddei-Ferretti, ed., Singapore, London: World Scientific, Vol. 1, pp. 273-279. ISBN/ISSN: 981-02-3228-4.

In spite of the fact that no photoreceptive cells have been identified, Hydra respondes to a light pulse by a phase shift of its bioelectrical patterns. This unconventional kind of photosensitivity is named non-visual or non-image-forming photoreception and belongs to higher species, including human. HOME