Anatomy of the pallial tentacular organs of the scallop Nodipecten nodosus (Linnaeus, 1758) (Bivalvia: Pectinidae)

Tentacular organs comprise a variety of body projections that have specialized functions in several invertebrate phyla. In bivalve mollusks, tentacles of the mantle margin serve sensorial and secretory functions involved in predator detection and interactions with the surrounding environment. However, their morphological diversity, detailed anatomy, and functional roles have only been scarcely investigated. Bivalves from the family Pectinidae are of particular interest in this context given the diversity of pallial tentacles, including distinct tentacle types arising on different mantle folds, and even eye-bearing tentacles. Combining several microscopy techniques, the present study investigates the anatomy of tentacular organs in postmetamorphic stages (juveniles and adults) of the scallop Nodipecten nodosus (Linnaeus, 1758). Scallop tentacles are formed shortly after metamorphosis, and except for pigmentation, they grow with no major morphological modifications. Tentacular organs of N. nodosus comprise eye-bearing and short and long tentacles from the middle mantle fold as well as velar tentacles from the inner fold. Although all tentacle types share a common basic structure (i.e., ciliated epithelium, peripheral muscle bundles, and a central nerve), they exhibit marked differences in ciliary distribution, epithelial secretory activity, and type of muscle fibers. Cilia distribution at the distal tip of sensory papillae represents a unique condition for the long tentacles from the middle mantle fold, and mucous secretion is restricted to the middle fold tentacles (except for eyestalks). Strikingly, velar tentacles and middle fold tentacles exhibit striated and non-striated myofibers, respectively. The data presented herein are discussed in light of the functional anatomy of the bivalve mantle margin. (C) 2015 Elsevier GmbH. All rights reserved. (AU)