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Phalacroma gibbosum sp. nov.(Dinophyceae) from the southern Gulf of Mexico

Abstract:

Within the marine dinoflagellates, the order Dinophysales includes members with very distinctive morphology and ecology. During a survey of the phytoplankton from the southern Gulf of Mexico, three specimens of an unknown dinophysoid species were found in formalin-fixed net samples, and were studied by light and scanning electron microscopy. A new species is proposed and formally described: Phalacroma gibbosum sp. nov. Its most characteristic features are as follows:(1) a distinctive trapezoid shape,(2) epitheca low with an elevation in the dorsal part of the epitheca (hump),(3) cingular lists fairly developed, with strong but discontinuous ribs,(4) an elongation of the posterior end of the hypotheca,(5) a mamilliform structure in the ventral margin of the hypotheca, and (6) theca covered by deep, circular areolae, with small pores, one per 3–5 areolae. This new species is morphologically similar and presumably closely related to Phalacroma favus and P. rapa. Molecular phylogenetic studies grouped these two species together with true Phalacroma species (including the type species), and this is regarded as an indication that Phalacroma gibbosum is also a member of that genus.