Identifying adhesive components in a model tunicate

Tunicates populate a great variety of marine underwater substrates worldwide and represent a significant concern in marine shipping and aquaculture. Adhesives are secreted from the anterior papillae of their swimming larvae, which attach and metamorphose into permanently adhering, filter-feeding adults. We recently described the cellular composition of the sensory adhesive organ of the model tunicate Ciona intestinalis in great detail. Notably, the adhesive secretions of collocytes accumulate at the tip of the organ and contain glycoproteins. Here, we further explore the components of adhesive secretions and have screened for additional specificities that may influence adhesion or cohesion of the Ciona glue, including other carbohydrate moieties, catechols and substrate properties. We found a distinct set of sugar residues in the glue recognized by specific lectins with little overlap to other known marine adhesives. Surprisingly, we also detect catechol residues that likely originate from an adjacent cellular reservoir, the test cells. Furthermore, we provide information on substrate preferences where hydrophobicity outperforms charge in the attachment. Finally, we can influence the settlement process by the addition of hydrophilic heparin. The further analysis of tunicate adhesive strategies should provide a valuable knowledge source in designing physiological adhesives or green antifoulants. This article is part of the theme issue ‘Transdisciplinary approaches to the study of adhesion and adhesives in biological systems’.

Scanning Electron Microscopic Surface Study of Adhesive organ of Garra gotyla gotyla (Gray)

An attempt to study the adhesive organ of Garra gotyla gotyla inhabiting hill streams of Aravalli region has been made using scanning electron micro-scope. The results were compared with that of scanning electron microscop-ic studies of the adhesive organ of G. gotyla gotyla of the Himalayan region. The SEM study reveals that the upper fringed lip (UFL)and the lower lip or the posterior free labial fold (PFLF) bears short stub shaped tubercles (ST). These tubercles in turn bear numerous spines (S). The tubercles are covered with squamous epithelium (SE) indicating that spines are modified squamous epithelial cells. The margins of stub-shaped tubercles bear smaller spines; their size increases from margin to the centre. The surface ultrastructure of the adhesive disc of G. gotyla gotyla revealed the presence of hexagonal epithelial cells with elevated cell boundaries. Each spine is attached to callous pad with a broad base. The spines are used for anchorage to the substratum so that fish can scrap food even in fast current of water. Tubercles are used by fish for protection against mechanical injuries. Further these may be taxo-nomically used for conspecific recognition. Cumulative action of tubercles and mucus enables the fish to make firm hold on the substratum.

Ultrastructural characterization of the adhesive organ ofIdiosepius biserialisandIdiosepius pygmaeus(Mollusca: Cephalopoda)

Water drift and tidal rise make the use of bonding mechanisms beneficial for small benthopelagic or interstitial marine animals. Chemical adhesives for attachment are very common in molluscs; however, only a few cephalopods have glue producing organs. The family Idiosepiidae is characterized by an epithelial adhesive organ (AO) located on the posterior part of the dorsal mantle area. Previous morphological and histological studies described three non-glandular cell types (basal, interstitial and fusiform cells) and three glandular cell types (goblet, columnar and granular cells) containing protein and carbohydrate components. However, these studies provide different information about the nomenclature and characteristics of the cell types. The present ultrastructural analyses and a 3D reconstruction of the AO ofIdiosepius pygmaeusandIdiosepius biserialistherefore serve to investigate the cell distribution, the fine structure of the cells and possible interactions between the cells.We found that basal cells form a continuous cell layer along the basal membrane, overlapped by the other epithelial cells. Embedded in microvilli-covered interstitial cells the glandular cells are more or less evenly distributed within the AO. Goblet and granular cells are solitary glandular cells without conspicuous morphological characteristics, whereas the columnar cells are arranged in dense aggregations of 5–15 cells. Each columnar cell is enclosed by a narrow supporting interstitial cell which contains dense longitudinal filament strands. The secretory process of the cells in the aggregation is synchronized. Each columnar cell aggregate bears approximately two ciliated sensory fusiform cells. The fusiform cells are connected to a neuronal network, aligned along the epithelium base.The results suggest that the bonding system is affected by two secretory cell types (granular and columnar cells). Both are similar in content, synthesis and secretory process but columnar cells are embedded in a particular cell environment. It is unclear in what way this arrangement is associated with the function of the AO. The neurons in several parts of the AO point to a neuronal control of the bonding mechanism. Comparisons with the AO cells of other cephalopods provide no indications for a morphological relationship between the adhesive systems.