THREE SPECIES OF THE DIATOM GENUSCORETHRONCASTRACANE: STRUCTURE, DISTRIBUTION AND TAXONOMY

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Abstract
Three species of the marine planktonic diatom genus Corethron are recognized, and compared in detail using light and electron microscopy. The confusion in the use of some of the names given to taxa in the past is clarified, mainly based on differences in the morphology of the hooked spines. The commonly used combination, Corethron criophilum Castracane is discarded in favour of the earlier described entity, Actiniscus pennatus which was combined with Corethron in 1903 as Corethron pennatum (Grunow) Ostenfeld. The function of the tfiree types of spine found in the genus is discussed. It is proposed that the spines of the two species existing as single cells, C. pennatum and C. hystrix, serve to move apart and maintain separation of the cells in the ocean. Similar spines are found in C. inerme but there the cells are normally joined by linking spines to form long chains. The hooked spines have a similar role to play but we suggest that their main function is to secure the developing spine system in order to safeguard the cingulum until the new valves reach maturity.