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Nanoplankton from the Galapagos Islands: Michaelsarsia elegans Gran and Halopappus adriaticus Schiller (Coccolithophorids) with Special Reference to Coccoliths and their Unmineralized Components

Irene Manton, G. Bremer and K. Oates
Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
Vol. 305, No. 1123 (Mar. 27, 1984), pp. 183-199
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/2396135
Page Count: 25
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Nanoplankton from the Galapagos Islands: Michaelsarsia elegans Gran and Halopappus adriaticus Schiller (Coccolithophorids) with Special Reference to Coccoliths and their Unmineralized Components
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Abstract

Marine plankton flagellates attributable to Michaelsarsia elegans Gran (type species of its genus) and Halopappus adriaticus Schiller (sensu Gaarder) have been 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, have been re-interpreted, and information on others added or amplified. Some of the new details include the body coccoliths, which have been shown to be more complex than previously supposed, the bar-crystallites in particular being compound in both taxa. In addition, unmineralized components are shown to be present in all types of coccolith. They include patternless membranes spread across the proximal faces of body coccoliths and occupying the apparently vacant centres 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. It is concluded that 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, whereas coccolith substructure is phyletically more meaningful. This indicates that Michaelsarsia, to which H. adriaticus should be transferred, is more remote from the other two genera than has hitherto been supposed. Finally an attempt has been made, in the light of all the evidence, to assess for the first time the possible functional significance of the unmineralized coccolith components and some constructive suggestions have been tentatively formulated. The paper ends with a factual summary in the form of revised taxonomic diagnoses for M. elegans, M. adriaticus and the genus Michaelsarsia.

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