Hemoglobin‐containing cells of Neodasys (Gastrotricha, Chaetonotida). I. Morphology and ultrastructure

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Abstract
The overall anatomy of Neodasys as well as data for hemoglobin-containing cells are described. Hemoglobin-containing cells are shown to be mesodermal specializations constituting approximately 14% of the animal's total body volume (4.87 ± 104 μl). These globular cells (10–14 μm) are situated in two longitudinal rows, each dorsolateral to the straight gut. Branches from the cells enwrap perikarya of muscle and nerve cells whose mitochondria are found just below their respective plasmalemmata in intimate association with the hemoglobin-containing cells. The ground substance of the cytoplasm and nucleoplasm of these nearly organelle-free cells is extremely electron-dense and is presumed to represent the hemoglobin molecules. Locomotion analyses indicate that the cells can undergo a threefold change in linear dimension in 0.25 seconds, raising the possibility of convective mixing in these cells. Structural and ultrastructural comparisons with similar cells in adults of other species of Gastrotricha indicate that the hemoglobin-containing cells of Neodasys may be homologous to the socalled Y cells of other species, some of which contain myofilaments. A muscle-cell origin is considered for the evolution of hemoglobin-containing cells of Neodasys.