Open AccessThe luminescence is a feature of several marine planktonic organisms, such as bacteria, algae, cnidaria, ctenophores, crustaceans and pyrosomes, in particular, alot of pelagic crustaces have got luminescent organs (Ghirendelli, 1981, Gruner, 1994) useful for trophic, reproductive or defense purposes. Several calanoid copepods are luminescent and possess variously distribuited epidermal glands. In this paper the occurrence of luminescent gland openings in adults and copepodids of Metridia gerlachei sampled during the Italian Oceanographic Campaign in Antarctica 1987-88 in Terra Nova Bay (Ross Sea) is described by using scanning electron microscopy (SEM) techniques. The openings of cephalothorax luminescent gland has been observed and described with the aim to complete what is known about this subject (Pinero de Verdinelli, 1981), the occurrence of a gland opening, not previously described, has been reported. Considering the extreme characteristics of the environment also that this species seems to prefer to live in low-light waters (Crli et al., 1990, 1992a) as the constant light conditions during the Antarctic summer restrict its occurrence in surface waters, luminescent structures could have an adaptive significance both for reproduction and defence.