Paracentrotus coelomocytes

Queiroz, Vinicius, Arizza, Vincenzo, Vazzana, Mirella & Custódio, Márcio R., 2022, Comparative evaluation of coelomocytes in Paracentrotus sea urchins: Description of new cell types and insights on spherulocyte maturation and sea urchin physiology, Zoologischer Anzeiger 300, pp. 27-40 : 29-32

3.3. Morphology of mature coelomocytes in SEM preparations

Phagocytes showed a quite flat and vacuolated cytoplasm, with filiform or bladder-like cytoplasmic expansions and a large nucleus ( Fig. 2A and G ). Vibratile cells had a pronounced and usually central nucleus and a very spread cytoplasm. Unlike other cells with spherules, vibratile cells seem to be much fragile, losing spherule integrity and becoming much spread ( Fig. 2B and H ). The flagellum can be occasionally observed ( Fig. 2B ), but it is easily lost during preparations ( Fig. 2H ). Crystal cells showed a very spread cytoplasm, with no visible nucleus and a remarkable cubic crystalloid beneath a thin layer of the cell membrane ( Fig. 2C ). Progenitor cells are flat and round, with a large central nucleus surrounded by a thin layer of cytoplasm ( Fig. 2I ).

Red spherulocyte showed a remarkable thicker nucleus and a very flattened cytoplasm (almost spread), composed of a lattice of large and uniform spaces that contained the spherules ( Fig. 2D and J ). Though very difficult to find in SEM preparations, typical mature red spherulocytes exhibited round, loosely grouped, regular-sized spherules ( Fig. 2D inset). By contrast, colorless and granular spherulocytes showed a comparatively thicker cell, with well-delimited spherules of irregular sizes and shapes in colorless spherulocytes ( Fig. 2E and K ), or regular sizes and shapes in granular spherulocytes ( Fig. 2F and L ).

M1

Morphotypes M2

M3

Figures

Fig. 2. Scanning electron microscopy of mature coelomocytes in Paracentrotus sea urchins. A-F – coelomocytes of P. gaimardi; G-L – coelomocytes of P. lividus. A and G – Phagocyte; B and H – Vibratile cell; C – Crystal cell; I – Progenitor cell; D and J – Red spherulocyte; D inset – Typical mature Red spherulocyte; E and K – Colorless spherulocyte; F and L – Granular spherulocyte. Arrowhead = Flagellum; Asterisk = nucleus. Scale: A = 10 μm; B-L = 5 μm.