摘要: SYNOPSIS. In order for photoperiodic phenomena to be expressed by any animal, the organism must possess some sort of photoreceptor. This may in form an eye or extraocular receptor, and invertebrate phyla illustrate fantastic diversity design either receptor type. While all major photoreceptor organs one type another, best-studied groups are those with highly complex eyes. These include crustaceans, molluscs, polychaete annelids. Many species these eyes having extreme sensitivity, good spatial resolution, cases multiple spectral channels. a few taxa, known provide input circadian oscillators, which suggests that they also employed measurement photoperiod. Extraocular photoreceptors dermal ganglionic sense organs, feed into systems numerous invertebrates, from cnidarians molluscs arthropods.