Experimental Investigation on the Morphology and Adhesion Mechanism of Leech Posterior Suckers

Abstract

The posterior sucker of a leech represents a fascinating natural system that allows the leech to adhere to different terrains and substrates. However, the mechanism of adhesion and desorption has not yet to be elucidated. In order to better understand how the adhesion is performed, we analyzed the surface structure, adsorption movements, the muscles’ distribution, physical characteristics, and the adsorption force of the leech posterior suckers by experimental investigation. Three conclusions can be drawn based on the obtained experimental results. First, the adhesion by the posterior sucker is wet adhesion, because the surface of the posterior sucker is smooth and the sealing can only be achieved on wet surfaces. Second, the deformation texture, consisting of soft collagen tissues and highly ductile epidermal tissues, plays a key role in adhering to rough surfaces. Finally, the adhesion and desorption is achieved by the synergetic operation of six muscle fibers working in different directions. Concrete saying, directional deformation of the collagen/epithermal interface driven by spatially-distributed muscle fibers facilitates the excretion of fluids in the sucker venter, thus allowing liquid sealing. Furthermore, we found that the adhesion strength is directly related to the size of the contact surface which is generated and affected by the sucker deformation. Such an underlying physical mechanism offers potential cues for developing innovative bio-inspired artificial adhesion systems.

First record of Stibarobdella moorei (Annelida, Hirudinea, Piscicolidae) a marine leech parasitizing Octopus bimaculatus (Mollusca: Octopodidae) from the Mexican Pacific coast

“…The longitudinal section in the posterior sucker of S. moorei showed the presence of many mucous secretions in the ventral surface at the posterior end of the leech body. Additionally, in a cross section of the body wall of S. moorei, we observed muscular fi bers arranged in longitudinal form fi bers, analogous to the previous annelids descriptions of Feng et al (2015) consisting in different muscles fi bers, long and short longitudinal muscular fi bers, circular muscular fi bers and radial muscular fi bers. Other minor muscle fi bers can also be observed in the area below the epidermis of the sucker, and these are different from those of Whitmania pigra (Whitman, 1884) (Feng et al, 2015).…”

“…Additionally, in a cross section of the body wall of S. moorei, we observed muscular fi bers arranged in longitudinal form fi bers, analogous to the previous annelids descriptions of Feng et al (2015) consisting in different muscles fi bers, long and short longitudinal muscular fi bers, circular muscular fi bers and radial muscular fi bers. Other minor muscle fi bers can also be observed in the area below the epidermis of the sucker, and these are different from those of Whitmania pigra (Whitman, 1884) (Feng et al, 2015). Feng et al (2015) described the adhesion and desorption mechanism achieved by muscle fi bers working in different directions: the directional deformation of the dermis interface driven by spatially-distributed muscle fi bers facilitates the excretion of fl uids in the sucker venter, thus allowing liquid sealing (Feng et al, 2015).…”

“…Other minor muscle fi bers can also be observed in the area below the epidermis of the sucker, and these are different from those of Whitmania pigra (Whitman, 1884) (Feng et al, 2015). Feng et al (2015) described the adhesion and desorption mechanism achieved by muscle fi bers working in different directions: the directional deformation of the dermis interface driven by spatially-distributed muscle fi bers facilitates the excretion of fl uids in the sucker venter, thus allowing liquid sealing (Feng et al, 2015). It appears from above that the histology of the body wall of the present leech S. moorei is similar to that of the other leeches such as C. mastacembeli (Rahemo and Hama, 2013) and W. pigra (Feng et al, 2015).…”

“…Feng et al (2015) described the adhesion and desorption mechanism achieved by muscle fi bers working in different directions: the directional deformation of the dermis interface driven by spatially-distributed muscle fi bers facilitates the excretion of fl uids in the sucker venter, thus allowing liquid sealing (Feng et al, 2015). It appears from above that the histology of the body wall of the present leech S. moorei is similar to that of the other leeches such as C. mastacembeli (Rahemo and Hama, 2013) and W. pigra (Feng et al, 2015). The histology and morphology of cells observed in this study may not be suffi cient to provide evidence about their function.…”

“…Circular muscular fi ber (cm) is observed at the edge of the sucker. Minor muscle fi bers can also be observed in the area beneath epidermal tissues of the sucker and body joints, which according with Feng et al (2015), are considered radial muscular fi ber (Rmf). The posterior sucker shows a stratifi ed epithelium and the two lateral caecae of the crop champers surrounded by large cells (Fig.…”