Fig. 8

Histological details of the tentacles of Stephanella hina. Semithin sections. a Longitudinal section of the oral lophophoral base through the ring canal showing extension from the ring canal into the oral tentacles and longitudinally sectioned nuclei of the subperitoneal cells of the tentacles. b Slightly oblique cross-section of the lophophoral base. The tentacles on the right side are more proximal, with the tentacle coelom still embedded in a common extracellular matrix, whereas the sectioned tentacles on the left show individual tentacles already. The nuclei of the subperitoneal cells are visible on the right side. c Cross-section of retracted tentacles within the tentacle sheath. Note also the subperitoneal cells medially occluding the tentacle coelom in some areas of the retracted positions (right side of the image). d Close-up of cross-sectioned retracted tentacles showing subperitoneal cells bulging medially towards the tentacle coelom in the longitudinal axis of each tentacle. e & f Cross-sections of extended lophophores showing different attachment possibilities of the tentacles to the intertentacular membrane via thin pedicels (e) or with the abfrontal side of the tentacles completely integrated into the membrane (f). (g & h) Cross-sections of densely arranged tentacles (g) with a thin epidermal layer always present on the abfrontal side and a thicker epidermal layer on the frontal side. Cilia are mainly located on the lateral and frontal sides of the tentacles (h). Note a thick cilium (asterisk) extending from the upper tentacle in (h), possibly a latero-frontal cilium. Abbreviations: aft - abfrontal side of tentacle, ecm - extracellular matrix, en - endocyst, ep - epistome, epc - epistome coelom, fc - frontal cilia, fst - frontal side of tentacle, gh - ganglionic horn, itm - intertentacular membrane, lb. - lophophoral base, lc - lateral cilia, loc - lophophoral concavity, mo - mouth opening, ph - pharynx, nsp - nuclei of subperitoneal cells, rc - ring canal, spc - subperitoneal cells of tentacles, tc - tentacle coelom, ts - tentacle sheath