A possible chlorophycean affinity of some Neoproterozoic acritarchs

Two taxa of Neoproterozoic acritarchs of unknown affinity, Multifronsphaeri dium pelorium and Species A, are analysed by electron microscopic (SEM, TEM ) and chemical (micro-FTIR, pyrolysis GC-MS, thermal desorption-MS) methods . Both acritarch species are characterised by multi-branched processes and a remnant trilaminar sheath (TLS) structure. The TLS-bearing wall structure s in these acritarchs suggest a possible biological affinity to chlorophyte algaenan. The molecular data obtained from the two acritarchs were general ly similar and also consistent with a chlorophycean affinity. A significant aliphatic moiety is evident in these acritarchs as a short-chain series of n-alkene/alkane pyrolysates and prominent aliphatic IR bands. The restrict ed molecular-weight range (< C-20) of the n-alkene/alkane doublets and the lack of isoprenoid and other branched alkanes in the pyrolysates suggest a low degree of branching in the aliphatic component of these acritarch macro molecules. The significant methyl (CH3) IR signal was attributed to the ter minal groups of short ir-alkyl moieties. Alkylbenzenes, alkylphenols and al kylindoles were also significant pyrolysis products, indicating an aromatic component, although the latter two components may be attributed to artific ially- and/or diagenetically-formed melanoidin moieties. The macromolecular structure of Multifronsphaeridium sp. and Species A consists of short n-al kylpolymethylenic chains, probably linked via ether/ester bonds, with possi bly a small aromatic content. This study presents ultrastructural and molec ular evidence of a genetic relationship between Neoproterozoic acritarchs a nd Chlorophyceae. (C) 1999 Elsevier Science Ltd. All rights reserved.