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Diseases of Aquatic Organisms

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DAO 142:63-73 (2020)  -  DOI: https://doi.org/10.3354/dao03533

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

Thierry M. Work1,*, Elena Millard1,2, Daniela B. Mariani1,3, Tina M. Weatherby4, Robert A. Rameyer1, Julie Dagenais5, Renee Breeden1, Allison M. Beale6

1US Geological Survey, National Wildlife Health Center, Honolulu Field Station, Honolulu, HI 96850, USA
2College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA
3Federal Rural University of Pernambuco, Department of Veterinary Medicine, Recife, Pernambuco 52171-900, Brazil
4University of Hawaii, Pacific Biosciences Research Center, Biological Electron Microscope Facility, Honolulu, HI 96822, USA
5IAP World Services (under contract to the US Geological Survey), Cape Canaveral, FL 32920, USA
6Leeward Community College, Pearl City, HI 96782, USA
*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 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 had circulating phagocytes that were 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 physiological phenomena in this animal group.


KEY WORDS: Echinoderm · Hematology · Coelomocytes · Light microscopy · Electron microscopy


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Cite this article as: Work TM, Millard E, Mariani DB, Weatherby TM and others (2020) Cytology reveals diverse cell morphotypes and cellin-cell interactions in normal collector sea urchins Tripneustes gratilla. Dis Aquat Org 142:63-73. https://doi.org/10.3354/dao03533

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