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Morphology and cytochemistry of dissociated cells of Petrosia ficiformis (Porifera)

In the present paper we report the results of our study aimed to the morphological and cytochemical identification of dissociated Petrosia ficiformis cells, a sponge species common on the rocky shores of the Mediterranean Sea. Indeed, in most species classification of sponge cells is difficult for their high plasticity and totipotency, beside the absence of organs and tissues. In a 30‐year‐old classification, four main classes of sponge cells were identified: covering cells, scleroblast‐like cells, i.e. cells secreting the skeleton, contractile cells and archeocytes. After mechanical dissociation of the specimens collected in the Adriatic Sea, we identified three main cell types, with a diameter ranging from 2 µm to 20 µm: (i) choanocytes, very small cells (5 µm in diameter), (ii) archeocytes, intermediate size cells (from 5 to 10 µm in diameter), (iii) spherulous cells, very heterogeneous elements (8–20 µm in diameter). Indeed, the cytoplasm of these latter cells is filled by a variable number of granules, which confer peculiar cytochemical staining patterns. In addition, we also identified the relevant presence of symbiotic microorganisms, namely cyanobateria, preferentially distributed inside the ectosome.