OBSERVATIONS ON THE MORPHOLOGY AND SEXUAL REPRODUCTION OFCOOLIA MONOTIS(DINOPHYCEAE)1

Abstract

ABSTRACTThe surface morphology of the dinoflagellateCoolia monotisMeunier was compared with the surface morphologyof Ostreopsis, The apical pore ofC. monotisis similar in architecture to that ofOstreopsisbut considerably longer (12 μm) than inO. heptagona(8–9 μm) andO. ovata(6–7 μm). A ventral pore inC. monotisis located on the right ventral margin between apical plate l′ and precingular plate 6″ and is similar in appearance and location to the ventral pore ofO. ovata.The longitudinal flagellum (20 μm) inC. monotisis longer than inO. ovata(12 μ). AlthoughCooliaandOstreopsisappear to be distinctly different and should remain as two separate genera, they appear to be related.Cells ofC. monotisdivided by binary fission. Doubling time was 3–4 days in the logarithmic phase of growth at 23°C, 12:12 h L:D, 30–90 μE‐m−2·s−1, and a salinity of 36%. Cultures reached cell densities of 2.5 × 103cells·L−1after 15 days of growth.The sexual process inC. monotisoccurred in Erdschreiber's medium when Danish soil extract was substituted with mangrove sediment extract under the culture conditions described above. Gamete fusion produced large biflagellated planozygotes (70–75 μm diam). Planozygote maturation involved cytoplasmic reorganization, loss of motility, development of a spherical shape (80–90 μm diam), and two to three orange accumulation bodies. The cells at this stage appeared to be thin‐walled cysts. Further development included reorganization of cyst contents, emergence of non‐motile gametes, and development of chloroplasts, sulcus, and girdle. The nucleus of the newly formed cells occupied 50% or more of the total cell volume. Meiosis occurred in the cyst, but nuclear cyclosis was not observed. Four daughter cells were produced within 36–48 h, and motile gametes developed. The gametes exhibited sexuality for 2 months and completed the sexual life cycle by going through a thin‐walled cyst stage.