Nanoplankton from the Galapagos Islands: michaelsarsia elegans gran and halopappus adriaticus schiller (coccolithophorids) with special reference to coccoliths and their unmineralized components

Publisher Website
Google Scholar
Abstract
Marine plankton flagellates attributable to M. elegans Gran (type species of its genus) and H. adriaticus Schiller (sensu Gaarder) were investigated by means of scanning and transmission electron microscopy supplementing light microscopy of dry whole mounts prepared in situ in the Galapagos Islands. Some external features, notably coccolith arrangement, are reinterpreted, and information on others added or amplified. Some of the new details include the body coccoliths, which are more complex than previously, supposed, the bar-crystallites in particulate being compound in both taxa. Unmineralized components are present in all types of coccolith. They include patternless membranes spread across the proximal faces of body coccoliths and occupying the apparently vacant centers of ring-shaped coccoliths, while a highly characteristic, fragile, reticulum is limited to the central areas of the elongated appendage links in both taxa. The impact of these findings on general biological concepts is discussed in a preliminary way, drawing on cognate data previously published for Ophiaster and Calciopappus. The presence of apical appendages (anterior or posterior) in each of these genera is an independently acquired adaptation to some as yet unknown environmental factor or factors; coccolith substructure is phyletically more meaningful. This indicates that Michaelsarsia, to which H. adriaticus is transferred, is more remote from the other 2 genera than was hitherto supposed. An attempt was made, in the light of all the evidence, to assess for the 1st time the possible functional significance of the unmineralized coccolith components, and some constructive suggestions were formulated. A factual summary is given in the form of revised taxonomic diagnoses for M. elegans, M. adriatus and the genus Michaelsarsia.