Fig. 1

A benthic ctenophore, Vallicula multiformis. a A phylogenic tree indicating relationships of metazoan phyla and those of the orders of Ctenophora (redrawn and modified from Whelan et al. 2017 [10]). The phylum Ctenophora is the earliest branch of the Metazoa. Most ctenophore species are pelagic, whereas those belonging to the Platyctenida are benthic as adults. b An aboral view of an adult V. multiformis. It attaches to substrates with its flat body and captures prey using a pair of tentacles (tc). c Magnified brightfield image of the aboral surface. The position of the aboral organ (ao) (also called apical organ) and tentacle sheathes (ts) are indicated. d The DIC image of the peripheral end of the body. The internal branching gastrovascular canal (gc) is observed. e The magnified brightfield image of the aperture of the tentacle sheath and elongating tentacles. f The DIC images of the main trunk (top) and tentilla (bottom) of the tentacle. The surface of the tentacles is covered with colloblasts (arrowheads), the ctenophore-specific adhesive cells used for capturing prey. Scale bar, 1 mm (b), 500 μm (c), 200 μm (d) and 50 μm (e, f)