The Role of Podial Secretions in Adhesion in Two Species of Sea Stars (Echinodermata)

Abstract

Individuals of Asterias rubens and Marthasterias glacialis use their podia in locomotion, anchorage, and feeding. Each podium consists of a stem with a disk at its tip. The stem allows the podium to lengthen, flex, and retract, and the disk allows the podium to adhere to the substratum. Adhesion of sea star podia seems to rely on the epidermal secretions of the disk and not on a mechanical sucker-like operation. The disk epidermis is made up of five cell types: nonciliated secretory cells (NCS cells) of two different types (NCS1 and NCS2), both containing granules that are at least partly mucopolysaccharidic in composition; ciliated secretory cells (CS cells) containing small granules of unknown content; nonsecretory ciliated cells (NCS cells); and support cells. The epidermal cells of the podial disk are presumably functioning as a duogland adhesive system that is involved in an adhesive/deadhesive process. The following model is presented. Adhesive secretions are produced by NCS1 and NCS2 cells (both of them have extruded some of their secretory granules in attached podia). These secretions constitute a layer of adhesive material between the podium and the substratum, this layer being the footprint left by the podium after it has become detached from the substratum. Deadhesion, on the other hand, would be due to CS cell secretions. All these secretions would be controlled by stimuli perceived by the two types of ciliated cells (receptor cells), which presumably interact with the secretory cells via the nerve plexus.

Sea star tenacity mediated by a protein that fragments, then aggregates

“…2 E and F). These ellipsoid granules (0.6 × 1 μm) have a complex ultrastructure, most of their volume being occupied by a bundle of parallel rods approximately 30 nm in diameter (37). It is at the level of these rods that we observed an extensive immunoreactivity (Fig.…”

“…In these proteins, cleavage apparently is autocatalytic, occurring at low pH in the late secretory pathway, or at neutral pH in the endoplasmic reticulum (31)(32)(33). A similar mechanism could also occur during the progression of Sfp1 from rough endoplasmic reticulum cisternae, through the Golgi apparatus, to the maturing secretory granules in the tube foot adhesive cells (37). It would generate four protein fragments (namely Sfp1α, Sfp1β, Sfp1γ, and Sfp1δ) with calculated molecular weights of, respectively, 57 kDa, 231 kDa, 72 kDa, and 66 kDa (Fig.…”

“…In A. rubens, previous investigations have clearly demonstrated that the adhesive material is released by the two types of adhesive secretory cells occurring in the disk epidermis of the tube feet (16,17,37). Type 2 adhesive cells are the first to release their contents and are responsible for the formation of the homogeneous film covering the substratum.…”

“…Indeed, more fibrillar material is deposited on surfaces to which the animal adheres strongly (e.g., glass and mica) than on surfaces on which adhesion is weak (e.g., Teflon) (17). The secretion of Sfp1 therefore appears to be correlated to strong adhesion and could be triggered by sensory cells via the nerve plexus (37). In other sea star species, much less information is available.…”

Intra- and interspecific variation of attachment strength in sea urchins

“…After detachment, the maximum force required to dislodge the sea urchin was recorded, as well as the angle of pull (0, 45 or 90°from the plane of the substratum), which varied according to the animal's position in the aquarium (on the side wall, in the corner or on the bottom, respectively). The glass plate(s) to which the animal was attached were removed from the aquarium, the broken tube feet were counted and discarded, and the plate(s) immediately immersed in a 0.05% aqueous solution of the cationic dye crystal violet for 1 min, in order to stain the footprints left by the tube feet (Flammang et al 1994, Santos & Flammang 2006. Digital photographs of the plate(s) bearing footprints were taken, each picture being calibrated with a piece of millimetric paper (Fig.…”