Galactogen is a polymer of galactose with species-specific structural variations. In this polysaccharide, the D-galactose are predominantly β (1→3) and β (1→6) linked; however some species also have β (1→2) and β (1→4). The galactogen of the aquatic Basommatophora (e.g. Lymnaea, Biomphalaria) is highly branched with only 5-8 % of the sugar residues in linear sections, and β(1→3) and β(1→6) bonds alternate more-or-Iess regularly. In the terrestrial Stylommatophora (e.g. Helix, Arianta, Cepaea, Achatina) up to 20% of the sugar residues are linear β(1→3) bound. The galactogen of Ampullarius sp species has an unusually large proportion of linearly arranged sugars, with 5% β(1→3), 26% β(1→6), and 10% β(1→2). Other analyses in Helix pomatia suggested a dichotomous structure, where each galactopyranose unit bears a branch or side chain.
Molecular weight determinations in galactogen extracted from the eggs of Helix pomatia and Limnaea stagnalis were estimated in 4x10 and 2.2x10, respectively. In these snails galactogen contains only D-galactose. Depending upon the origin of the galactogen, apart from D-galactose, L-galactose, L-fucose, D-glucose, L-glucose and phosphate residues may also be present; for instance, the galactogen from Ampullarius sp. contains 98% of D-galacotose and 2% of L- fucose, and the one isolated from Pomacea maculata eggs consist in 68% of D-galactose and 32% of D-glucose. Phosphate-substituted galactose residues are found in the galactogen of individual species from various snail genera such as Biomphalaria, Helix and Cepaea. Therefore, current knowledge indicates it could be considered either a homopolysaccharide of or a heteropolysaccharide dominated by galactose.