actin–myosin system and left behind as a mucus trail. The mucus strands can be fused
together or remain as individual strands (Fig. 2.7c & d).
Fig. 2.6 SEM of the pennate diatom Navicula cuspidata, showing the central raphe.
(^) (Courtesy of E.G. Vrieling, Department of Marine Biology, Centre for Ecological and Evolutionary Studies,
University of Groningen, The Netherlands, with permission from the Journal of Phycology.)
Fig. 2.7 Model of gliding locomotion in diatoms. (a) Strands of adhesive mucilage
secreted by the diatom adhere to the substrate but also remain connected to
components of the diatom cell membrane. These membrane elements are actively
translocated rearward upon a framework of actin filaments, leading to the forward
movement of the diatom relative to the substrate. At the rear of the cell, mucilage
strands break and are deposited as a trail.
(After Edgar & Pickett-Heaps 1983.)
(b) Model for the organization of the motor apparatus in diatoms. Excreted musilage
adheres to the substrate and to a membrane-associated complex that is linked to a
diatom myosin. The myosin translocates the membrane complex and attached
mucilage rearward along a tract of actin filaments leading to the forward gliding of
the diatom.
(^) (After Heintzelman 2006.)
(c and d) scanning electron micrographs (SEMs) of chemically fixed mucoid trails
deposited by Pinnularia viridis. The adhesive strands protruding from most of the
raphe may be fused together (c) or remain as individual strands (d).
(^) (c and d after Higgins et al. (2003), with permission from the Journal of Phycology.)