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Diseases of Aquatic Organisms

    DAO prepress abstract   -  DOI: https://doi.org/10.3354/dao03533

    Cytology reveals diverse cell morphotypes and cell-in-cell interactions in normal collector sea urchins Tripneustes gratilla

    Thierry M. Work*, Elena Millard, Daniela B. Mariani, Tina M. Weatherby, Robert A. Rameyer, Julie Dagenais, Renee Breeden, Allison M. Beale

    *Corresponding author:

    ABSTRACT: Echinoderms such as sea urchins are important in marine ecosystems, particularly as grazers, and unhealthy sea urchins can have important ecological implications. For instance, unexplained mortalities of Diadema antillarum in the Caribbean were followed by algal overgrowth and subsequent collapse of coral reef ecosystems. Unfortunately few tools exist to evaluate echinoderm health making management of mortalities or other health issues problematic. Hematology is often used to assess health in many animal groups including invertebrates but is seldom applied to echinoderms. We used a standard gravitometric technique to concentrate fixed coelomocytes from the collector sea urchin Tripneustes gratilla onto microscope slides permitting staining and enumeration. Using Romanowsky stain and electron microscopy to visualize cell details, we found that existing urchin cells could be partitioned into different morphotypes. Specifically, we enumerated phagocytes, phagocytes with perinuclear cytoplasmic dots, vibratile cells, colorless spherule cells, red spherule cells, and red spherule cells with pink granules. We also saw cell-in-cell interactions characterized by phagocytes apparently phagocytizing mainly the motile cells including red spherule cells, colorless spherule cells, and vibratile cells disproportionate to underlying populations of circulating cells. Cell-in-cell interactions were seen in 71% of sea urchins, but comprised <1% of circulating cells. Finally, about 40% of sea urchins have circulating phagocytes that are apparently phagocytizing spicules. The coelomic fluid collection and slide preparation methods described here are simple, field portable, and might be a useful complementary tool for assessing health of other marine invertebrates revealing heretofore unknown physiologic phenomena in this animal group.