Morphology and Molecular Phylogeny of a New Marine Sand-dwelling Prorocentrum Species, P. tsawwassenense (dinophyceae, Prorocentrales), from British Columbia, Canada(1).

A new marine benthic, sand-dwelling Prorocentrum species from the temperate region of the Pacific coast of British Columbia, Canada, is described using LM and EM and molecular phylogenetic analyses. The cells have a broad oval shape, 40.0-55.0 μm long and 30.0-47.5 μm wide, and a wide U-shaped periflagellar area on the right thecal plate. The left thecal plate consists of a straighter apical outline in the form of a raised ridge. Five to six delicate apical spines in the center of the periflagellar area are present. The nucleus is located in the posterior region of the cell, and a conspicuous pusule is located in the anterior region of the cell. The cells have golden-brown chloroplasts with a compound, intrachloroplast pyrenoid that lacks a starch sheath. The thecal plates are smooth with round pores of two different sizes. The larger pores are arranged in a specific pattern of radial rows that are evenly spaced around the plate periphery and of irregular rows (or double rows) that form an incomplete "V" at the apical end of the plates. Large pores are absent in the center of the left and right thecal plates. The intercalary band is striated transversely and also has faint horizontal striations. Trichocysts and two types of mucocysts are present. The molecular phylogenetic position of Prorocentrum tsawwassenense sp. nov. was inferred using SSU rDNA sequences. This new species branched with high support in a Prorocentrum clade containing both benthic and planktonic species.