Sticking with it: Footprints of the Starfish

The most common starfish found in Irish waters, and in the north-east Atlantic as a whole, Asterias rubens can be found in quite deep waters, but is usually found in the intertidal region where it feeds on a variety of molluscs (1). The quantity of prey to be found is quite high here, but so are the challenges posed to A. rubens. These chiefly come from the disruptive action of waves, which can easily wash individuals onto the shore line, which is just what happen to the starfish pictured.
 

Common Starfish, Asterias rubens

A. rubens overcomes this by the ingenious use of adhesives. The numerous tube feet located on the underside of the animal that are used for locomotion, secrete globular nanostructures forming a meshwork deposited on a thin homogeneous film (2). Two cell types have been identified in the production of this adhesive material:- type 1 cells, which produce the material forming the meshwork, and type 2 cells which are responsible for the release of the material constituting the homogeneous film. These will leave behind a footprint with a reticulate pattern on the substrate. This pattern is due to the arrangement of the adhesive cell secretory pores on the disc surface of the tube feet.

References:

1. Allen, 1983. Journal of Experimental Marine Biology and Ecology 70 pp. 79-90
2. Hennebert et al., Journal of Structural Biology 164 (2008) 108–118