Histochemical and ultrastructural analysis of the epidermal gland cells of Branchiomma luctuosum (Polychaeta, Sabellidae)

. This histochemical and ultrastructural study describes the epidermal gland cells of a tubicolous polychaete, Branchiomma luctuosum. The histochemistry was carried out using standard techniques and FITC-labelled lectins. Four types of secretory cells were identified in two categories: orthochromatic cells (Type 1) and metachromatic cells (Types 2, 3, and 4). The secretory product of the Type-1 orthochromatic cells contains neutral glycoproteins with Galβ1,3GalNAc residues. Metachromatic cells produce acidic, mainly sulfated, glycoconjugates with Galβ1,3GalNAc residues (Type 2) or glucosidic and/or mannosidic residues (Types 3 and 4). In sialylated chains, terminal sialic acid is bound to the penultimate GalNAc and Galβ1,3GalNAc residues. The complex composition of the mucus produced by epidermal gland cells of B. luctuosum may be correlated with its different functions. Ultrastructural studies of the epidermal gland cells showed differing morphology, and the presence in the gland cells of Types 3 and 4 of a funnel-shaped structure for the extrusion of the secretory material.