Pheophytin (Pheo) is structurally constituted as to make possible certain reactions, previously given very little attention, which appear to play crucial roles in the initial electron transfer (ET) processes. The transformations involve enolisation with subsequent formation of mono- and di-iminium cations at the Pheo core. The important impact of these ions on ET from chlorophyll (Chl) to Pheo and then to quinone are evaluated. These insights rationalise the long-standing enigmas of fast transfer, across gap ET, activation-less aspect, and essential lack of reversibility. Comparisons are made to other important areas of iminium involvement, e.g. chemistry of vision, polyaniline doping, and DNA alkylation.
Nine Pteromylaeus bovinus (F., Geoffroy St. Hilaire) (Euselachii: Myliobatinae) from the Tunisian coast were examined l'or ectoparasites during 1995, 1996 and 1997. A monogenean found on the gills of seven host specimens is described as a new species and a new genus, Heliocotyle, is proposed to accomodate it. The presence of a single sclerotized haptoral structure on the dorsal surface of the haptor leads us to place this species in the Heterocotylinae Chisholm, Wheeler ct Beverley-Burton, 1995. The genus Heliocotyle is characterized by a haptor with only one dorsal structure and seven loculi, six being subdivided by pseudosepta. Heliocotyle kartasi sp. n. is the type and the only species in this genus.