Morphology and taxonomy of the marine planktonic dinoflagellate Centrodinium pulchrum B?hm (Dinophyta) from the tropical Mexican Pacific, with comments on the taxonomy and distribution of the genus Centrodinium

摘要

Centrodinium pulchrum B?hm, a rather large thecate dinoflagellate, has been found in samples from the tropical Mexican Pacific and studied in detail by light microscopy and scanning electron microscopy to define its morphological variation and tabulation. General morphological features, previously found in other members of the genus, were also found in this species: the cell body is biconical and laterally compressed with two extensions; the cingulum is median, descending and lacking lists; the theca is hyaline; and chloroplasts are present. The plate formula, which can be extended to the genus Centrodinium, is interpreted as 3′, 3a, 6″, 6c, 5s, 5′″, 2p, 1″″. Some specimens were found forming short chains (two to three cells) during presumably developing stages; associated attachment structures consisted of two relatively large pores, one in epitheca, close to the apical pore, the other in the middle hypotheca. Centrodinium pulchrum is morphologically very similar to Centrodinium eminens, and possibly to Centrodinium complanatum, and closely related. However, despite morphological variation, the apical horn of C. pulchrum was consistently wide and truncated, with a conspicuous crest on the anterior dorsal margin, and we detected no overlap or intergrades among the species. A new family, Centrodiniaceae Hernández-Becerril fam. nova, is proposed to accommodate the genus because of the differences with the supposedly related genus Oxytoxum and associated genera of the family Oxytoxaceae Lindemann. The new combination Centrodinium ovalis (Pavillard) Hernández-Becerril comb. nov. is proposed for Murrayella ovalis Pavillard. All species of the genus are in need of study, and the relationship with presumably related genera, such as Pavillardinium, needs to be examined. The genus Centrodinium is distributed mainly in warm-water (tropical and subtropical) regions, but it is rather rare and not abundant.