PUB - Publikationen an der Universität Bielefeld

In the present study the nidamental glands of 32 species of opisthobranchs, belonging to the "Cephalaspidea s. l.", Anaspidea, Sacoglossa, Tylodinoidea, Pleurobranchoidea and Nudibranchia and of five species from outgroup taxa (Pyramidelloidea, Pulmonata and Gymnomorpha) have been investigated histologically, histochemically and ultrastructurally. The egg masses of nineteen opisthobranch taxa and one pulmonate species have also been studied with the same techniques. Generally speaking, the structure of the nidamental glands is rather uniform in the investigated species: all species possess three distinct glandular parts, namely an albumen or a capsule gland, a membrane gland and a mucous gland. An albumen gland is present in some "Cephalaspidea s. l.", all Anaspidea and all Sacoglossa, as well as in the outgroup taxa whereas some "Cephalaspidea s. l.", all Tylodinoidea, all Pleurobranchoidea and all Nudibranchia possess a capsule gland instead. A membrane and a mucous gland are found in all investigated species. The epithelia of all glandular parts have the typical arrangement of alternating glandular cells and supporting cells. The glandular cells contain the secretory products whereas the supporting cells bear cilia. The secretory products can have the form of distinct granules (albumen and capsule glands) or be of heterogeneous, filamentous shape (membrane and mucous glands). The contents of the secretory products are neutral mucopolysaccharides and proteins in the albumen und capsule glands and acidic, sulphated as well as neutral mucopolysaccharides in the membrane and mucous glands. These substances can also be found in according layers in the egg masses. The egg masses also have a uniform structure throughout the taxa. Generally the embryos are encapsulated in a distinct capsule, which is composed of one membrane layer in those species which possess an albumen gland in their nidamental system. In these species a viscous albumen fluid is also present in the egg capsules. Those species which possess a capsule gland have two layered egg capsules, one outer membrane layer and one inner albumnineous layer. Albumen fluid is missing in the egg capsule of these species. In all investigated taxa the egg capsules themselves are surrounded by an inner mucous layer, are embedded in a mucous matrix and the whole egg mass is surrounded by a multi-layered outer mucous cover. Differences in this fine structure are found in the number of embryos per capsule, the number of capsules per egg mass and the fine structure of the various mucous layers. In this study the possible homologies of the different glandular parts of the nidamental glandular system as well as the homologies of the different layers in the egg masses throughout the Opisthobranchia are discussed. Aspects of functional morphology are presented. Moreover a hypothetical scenario of the evolution of the nidamental glandular system is proposed and the phylogenetic implications are discussed.