Visualization of the Lytechinus pictus egg jelly coat in platinum replicas

The jelly coat of Lytechinus pictus is composed of a three-dimensional network of interconnected fibers. Both the jelly ultrastructure and its individual molecular components were visualized using rotary-shadowed platinum/carbon replicas. Bulk egg jelly, shed dry onto mica chips, displays large rope-like strands composed of bundles of smaller fibers associated with an amorphous ground substance. Additional fibers extend laterally from the rope-like strands forming branching networks. Isolation of the major fucose sulfate-rich polysaccharide complex showed that its overall structure is similar to that of whole egg jelly. Individual molecular components of jelly, separated by acid extraction and sprayed onto mica chips in 50% glycerol, exhibit repeating topological features including branching and large numbers of internal and terminal loops. Size and complexity of individual components range from small circular molecules of less than 50 nm in diameter to highly branched networks exceeding 9.5 μm in total length.