In vitro culture of tissue from the tunicate Styela clava

Pharyngeal explants and circulatory hemocytes from the tunicate Styela clava were cultured in a medium containing tunicate plasma, artificial seawater, RPMI 1640, and antibiotics. Pharyngeal tissue remained viable and proliferated for up to 72 d in vitro. Proliferative activity maintained the pool of hemocytes within explants and facilitated the migration of pharyngeal hemocytes from explants into culture supernatants. The diversity of morphologically distinct cell types within the hemocyte pool of pharyngeal cultures indicated that cell division was followed by regulated differentiation. In contrast to pharyngeal cultures, suspensions of circulatory hemocytes did not survive for prolonged periods in vitro. Proliferative activity could not be detected in circulatory hemocyte cultures. These results are discussed in terms of the differentiation state of hemocytes and the efficacy of culture conditions.