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Diversity and distribution of extracellular microcrystals in holothuroid echinoderms
Kevin C K Ma1, Fei Gao1,2, Jean-François Hamel3
1Department of Ocean Sciences, Memorial University, St. John's, Newfoundland and Labrador, Canada.
Royal Society Open Science
|September 19, 2025
Summary
Echinoderms possess novel extracellular microcrystals, including uric acid, calcium carbonate, and calcium oxalate dihydrate. These findings expand our understanding of biomineralization beyond skeletal structures in echinoderms.
Area of Science:
- Marine Biology
- Biomineralization
- Echinoderm Physiology
Background:
- Echinoderm biomineralization research traditionally focuses on skeletal elements.
- Extracellular microcrystals have not been previously documented in echinoderms.
Purpose of the Study:
- To identify and characterize novel extracellular microcrystals in holothuroids.
- To investigate the potential roles of these microcrystals in echinoderm physiology.
Main Methods:
- Isolation and classification of six morphotypes of extracellular microcrystals.
- Chemical analysis to determine crystal composition (uric acid, calcium carbonate, calcium oxalate dihydrate).
- Microscopic examination of crystal location and association with cellular structures.
Main Results:
- Uric acid crystals found in hydrovascular system, perivisceral coelom, and respiratory tree fluids, often encapsulated by phagocytes.
- Calcium carbonate crystals detected in the respiratory tree epithelium.
- Calcium oxalate dihydrate crystals identified in cloaca, integument, Polian vesicle, and tentacles.
Conclusions:
- The identified microcrystals represent a new facet of biomineralization in echinoderms.
- Uric acid crystals likely function as waste products.
- Calcium carbonate and calcium oxalate dihydrate crystals suggest roles in excretion and potentially calcium regulation/storage for skeletal repair.
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