Amphidinium operculatum var. nov. gibbosum (dinophyceae), a free-swimming marine species producing cytotoxic metabolites

Abstract

A single-cell isolate of Amphidinium from the northern Caribbean Sea was identified as A. operculatum Clap. et Lach. var. nov. gibbosum Maranda et Shimizu based on a morphological and ultrastructural study. This free-swimming dinoflagellate, which was found to produce potent antitumor metabolites, is elongate and asymmetrical. It is compared with two close relatives A. klebsii Kofoid et Swezy and A. carterae Hulburt. Amphidinium operculatum var. gibbosum can be distinguished from A. klebsii on the basis of shape while it differs from A. carterae on the basis of size, shape, cell surface, and chloroplast arrangement. The shape and size of the nucleus and the presence of mucocysts also differentiate the gibbosum variety from its two relatives. The architecture of the pusule may ultimately provide the best ultrastructural discriminating character. Otherwise, the general ultrastructure of the Caribbean isolate is typical of many unarmored photosynthetic dinoflagellates with amphiesma, condensed chromosomes, trichocysts, mitochondria with tubular cristae, and trilamellar chloroplasts.