Background and Aims:

Within phytoplankton, diatoms are the most studied, even though confusions in identification still occur among species of some genera like Actinoptychus. The aims of this work was to determine and describe the morphology of the species of the genus Actinoptychus, present the new records that occur in the coastal area of Oaxaca, Mexico, and review the distribution of the species of this genus recorded in the Mexican Pacific.

Methods:

Twenty-four samples from five localities were analyzed: Corralero and Chacahua coastal lagoons, and Cacalotepec, Punta Colorada and Bahía Grande neritic zones in Oaxaca. A cleansing of frustules was performed, and permanent slides were made for identification. Specimens were observed in optical microscopy.

Key results:

Five species were identified on the coast of Oaxaca: Actinoptychus splendens, A. vulgaris, A. concentricus, A. aster and A. senarius, being A. aster, A. concentricus and A. vulgaris new records for the state. Detailed descriptions are provided for each taxon.

Conclusions:

The distribution range of Actinoptychus aster, A. concentricus and A. vulgaris is extended for the Mexican Pacific. The size intervals previously reported in the Mexican Pacific for A. aster, A. senarius and A. vulgaris are extended here. Additionally, morphometric and meristic data for A. concentricus are reported for the first time.

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