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an asexual spore characteristic of red algae and some brown algae (Dictyotales). Tetraspores are formed in groups of four in a tetrasporangium as a result of the meiosis of the nucleus. They arrange themselves in the shape of a tetrahedron or sometimes in the shape of a square or in a single line. Tetraspores lack organs of locomotion. After the spores settle, the thin sheath that encases them thickens and the spores germinate.