2Author for correspondence: e-mail Annemarie.Schmid@sbg.ac.at.
THE “PARADOX” DIATOM BACILLARIA PAXILLIFER (BACILLARIOPHYTA) REVISITED1
Article first published online: 16 FEB 2007
Journal of Phycology
Volume 43, Issue 1, pages 139–155, February 2007
How to Cite
Schmid, A.-M. M. (2007), THE “PARADOX” DIATOM BACILLARIA PAXILLIFER (BACILLARIOPHYTA) REVISITED. Journal of Phycology, 43: 139–155. doi: 10.1111/j.1529-8817.2006.00299.x
1Received 27 October 2005. Accepted 28 August 2006.
- Issue published online: 16 FEB 2007
- Article first published online: 16 FEB 2007
- cell adhesion;
- cell wall;
- fibulate raphe system;
Defined by its unique colonial locomotion, Bacillaria paxillifer (O. F. Müll.) Hendey was recognized as a single, pandemic species by many phycologists. However, reinvestigation of colonies from different habitats revealed three distinct groups: (A) brackish/freshwater, (B) marine littoral, and (C) marine planktonic taxa. Groups differed in colony and cell form, raphe flanges (RFs), shape and position of transapical ribs (Tr's), and morphogenesis. Linear-shaped species were restricted to group A: Tr's thickened principally to the interior. Lanceolate forms were confined to groups B and C: valve formation proceeded from an internal base layer to the exterior. The planktonic species differed in the shape of its raphe slit, and the transformation of girdle bands (GBs) into “winglets.” Taxa also differed in chloroplast shape and number. All species formed motile colonies. Siblings adhered via elastic fibrils secreted through their raphe. Raphe ribs were held in position by siliceous clamps (fibulae), anchored in an extra pair of axial ribs (fibular ribs) parallel to the raphe ribs. This raphe system resembled that of Cylindrotheca rather than the “canal raphe” of Nitzschia. Many valves were asymmetric along the apical axis due to protruding RFs shuttling in a 1:1 ratio within a colony, but raphe slits were mirror images, as were the growth direction of fibulae and position of plastids, with pyrenoids tilted in the same direction. Species possessed four open GBs per epitheca; the third band invariably bore an internal, organic ridge to aid in adhesion of the plasmalemma during cleavage. The results suggested that these taxa are a natural phylogenetic group, requiring precise determination of their taxonomic position.