Abstract

HERNANDEZ ROSAS, Adriana; MEAVE DEL CASTILLO, María Esther; ZAMUDIO-RESENDIZ, María Eugenia  and  CASTILLO RIVERA, Manuel. Morphometry and distribution of species of the genus Ornithocercus (Dinophysiales: Dinophyta) from the Mexican Pacific. Hidrobiológica [online]. 2007, vol.17, n.3, pp.257-272. ISSN 0188-8897.

It is described, illustrated and indicated the distribution of nine taxa of Ornithocercus; two of them being new records for the Mexican Pacific. The results of morphometric analyses over seven Ornithocercus species (O. bilobatus, O. magnificus, O. heteroporus, O. galea, O. quadratus, O. steini and. O. thumii) are presented. We evaluated 29 variables on 90 organisms of different species collected in the Mexican Tropical Pacific coasts. Due to the overlapping between O. steini-O. thumii, special analyses were done for this complex. Data were analyzed with multivariate statistical tools, Cluster Analysis (CA) and Discriminant Analysis (DA). CA resulted in two main and well differentiated groups, one of them with O. thumii, O. steini and O. quadratus (as differentiated subgroups), a second one with O. magnificus, O. heteroporus and O. galea. The DA showed significant differences up to fourth function (λ Wilks<0.162, p<0.0005) with 97.7% of cases correctly classified and accumulated variance of 98.1%. The most important variables for segregation were the total length, the cingulum width and the rib R₃. Significant differences were found among epitecal area and cingulum width. We concluded that O. galea is different enough from O. quadratus so they are not varieties of a single species. Despite of the overlapping between O. steini and O. thumii we found meristic characters to differentiate them.

Keywords : Morphometry; Dinoflagellates; Ornithocercus; Mexican Pacific.