Abstract
The occurrence of the Mediterranean red alga Ceramium giacconei Cormaci et Furnari, in the northeastern Pacific Ocean (Gulf of California) is reported for the first time, associated with a rhodolith bed. Although C. giacconei is similar to C. cingulatum Weber-van Bosse, known from the Indian Ocean, our observations confirm the validity of C. giacconei as a distinctive species on the basis of the following features: 1) erect thallus markedly compressed above several basal segments, 2) complete cortication except the basal segments, 3) unequal development of corticating filaments, 4) oblong axial cells, 5) solitary and straight apex, 6) tetrasporangia immersed in cortex and produced from both periaxial and cortical cells, 7) spermatangia produced from cortical cells, 8) cystocarps surrounded by 4 or 5 involucral branches. Sexual reproductive structures are described for the first time and conform to previous reports of the genus.
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