Preliminary observations on differences of scale morphology at various stages in the life cycle of ‘<i>Apistonema-Syracosphaera’ Sensu</i>von Stosch

Abstract

A preliminary study of the fine structure of various stages in the life cycle of von Stosch's solate of 'Syracosphaera carterae' has been made by means of sections and whole mounts.Protoplast structure appears to be similar throughout the cycle.However, the Apistonema thallus possesses a cell wall composed of numerous layers of closely adpressed rimless unmineralised scales.Two types of asexual swarmers are shown to be covered with one or two layers of somewhat similar scales.One type of swarmer possesses a short haptonema which is covered with small scales.In addition the coccolith-bearing stages are shown to be identical with Hymenomonas carterae sensu Manton and Peterfi (1969) and this isolate has therefore been transferred to H. carterae.The culture of 'Syracosphaera' used for this study was isolated and described in a preliminary way by von Stosch (1955Stosch ( , 1958)).It was the first recorded coccolithophorid with a benthic phase.Further details of the life history were added later (von Stosch, 1967).Von Stosch (1955) referred to the coccolith-bearing cells as 'Syracosphaera-Panzerflagellaten' (Syracosphaera armoured flagellates) and he called the thallus the 'Heterococcus stage' owing to its similarity in both form and colour to the Xanthophycean genus Heterococcus.Von Stosch did not at first name the species but Braarud (1960) found that the coccoliths of this isolate were similar to those of Syracosphaera carterae Braarud et Fagerland.Accordingly, von Stosch (1967) used carterae as a specific epithet but retained Syracosphaera for the genus.There are exceptionally difficult problems associated with the naming of this isolate and hence it is useful to discuss briefly the nomenclature so that further confusion can be avoided.Originally, a free-living flagellate had been attributed to Syracosphaera brandtii Schiller by Carter (1937) but was later redescribed as a new species under the name of Syracosphaera carterae by Braarud and Fagerland (1946).However, Halldal andMarkali (1954) made an electron microscopical study of the coccoliths of a number of species of Syracosphaera and Braarud (1954), having similarly examined the coccoliths of Hymenomonas roseola Stein, transferred S. carterae to the genus Hymenomonas Stein.Later, Braarud (1960) created the new genus Cricosphaera for Hymenomonas-type cells with 'cricoliths '.Recently Manton and Peterfi.(1969) have shown that the microanatomy of Cricosphaera carterae sensu Braarud (1960) closely resembles that of Hymenomonas roseola and so they have returned C. carterae to the genus Hymenomonas Stein (Stein, 1878).