Fig. 9

S. alveolata. Branchiae, epidermis and peripheral blood vessels, TEM. a Unciliated epidermal supportive cells (suc) above branchial coelom (brcoe), basal blood space (bs) gives off several branches (arrowheads) extending towards surface, note receptor cell process (rc) with sensory cilium (sc), b Enlargement of boxed area in a to show minimal distance between blood space and cuticle (arrow), blood space bordered by ECM (ecm), c Blood space (bs) between supportive cells (suc), cuticle (cu) without collagen fibers traversed by a few microvilli (mv), extensions of hemocyte (bc) reach into blood space, d Densely ciliated cell (cc) belonging to curved ciliated band between unciliated supportive cells (suc), cells situated above inner branchial vessel (ibrv), coelomic side of vessel bordered by granulocyte-like peritoneal cells (pt) above ECM, e Glandular cell necks (gc) and multiciliated receptor cell process (rc) between supportive cells (suc); arrows point to deeply invaginated aperture of type-2 glandular cell, f Group of three receptor cells, cut in different planes, two unicilated with cell body (on the left), g Dendritic process with diminutive rootlets of sensory cilia (arrowheads), h Sensory cilia (sc) and basal bodies (bb) of dendritic process. Abbreviations: bb - basal body, bc - blood cell (haemocyte), brcoe - branchial coelom, bs - blood space, cc - ciliated cell, cl - cilium, cu - cuticle, ecm - ECM, gc - glandular cell, if - intermediate filaments, ibrv - inner branchial vessel, − mb multivesicular body, mf - myofilaments, mi - mitochondrion, mv - microvillus, nc - nucleus, pt - peritoneum, rc - receptor cell, sc - sensory cilium, sj - septate junction, suc - supportive cell, v - vesicle, za - zonula adherens