Article

Irregular helicoids in leech cocoon membranes.

Department of Biology, 315 Penn Street, Science Buliding, Rutgers The State University of New Jersey, Camden, NJ 08102, USA.
Journal of Structural Biology (impact factor: 3.41). 07/2007; 158(3):336-43. DOI:10.1016/j.jsb.2006.12.009 pp.336-43
Source: PubMed

ABSTRACT Helicoids in the cocoon membrane of leeches Theromyzon tessulatum and Erpobdella punctata comprise a twisted superposition of layers, each containing a variable number of planes formed by unidirectional fibrils. Straight fibrils intersecting at different angles were displayed in tangential sections through the cocoon wall of each species. When the sectioning angle was below a certain value (i.e., the critical angle), bow-shaped lines apparent in oblique sections were replaced by a succession of layers containing straight fibrils, permitting a direct measurement of step-angle change between successive layers in a helicoid. By this methodology, we determined that no regularities exist in the succession of step-angles or in layer thicknesses within the cocoon membranes, but that the distribution of step-angles between layers was unique for each cocoon type.

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Keywords

bow-shaped lines apparent
 
certain value
 
cocoon membrane
 
cocoon membranes
 
cocoon type
 
cocoon wall
 
different angles
 
direct measurement
 
fibrils
 
fibrils intersecting
 
Helicoids
 
layer thicknesses
 
layers
 
leeches Theromyzon tessulatum
 
oblique sections
 
step-angle change
 
successive layers
 
twisted superposition
 
unidirectional fibrils
 
variable number