Ultrastructure of the Epithelium and the Sensory Receptors in the Body Wall, the Proboscis and the Pharynx of Gyratrix hermaphroditus (Turbellaria, Rhabdocoela)

Abstract

The epidermis of Gyratrix hermaphroditus can be described as semi‐syn‐cytial. Its ultrastructure is characterized by microvilli and cilia with two strong rootlets perpendicular to each other. The apical part of the epithelium contains mitochondria and vacuoles. The basal synthesizing layer is provided with cell boundaries, at least between the type II penetrating receptors in the anterior and posterior end of the worm. Four different types of sensory receptors are described. The type I receptor has a protruding cilium‐bearing process and is found all over the body. The type II receptor is found in the anterior and posterior end and has a retracted process with a kinocilium surrounded by eight stereocilia. The type III receptor bears a balloon‐shaped modified cilium and is located at the anterior end. The type IV receptor has a short cilium with an unstable ciliary membrane and occurs in the proboscis epithelium as well as in the pharynx epithelium. Phylogenetical aspects of the semi‐syncytial epithelium and functional aspects of the sensory receptors are discussed.

Ultrastructure of the nerve cells and sensilla of Geocentrophora baltica (Platyhelminthes, Lecithoepitheliata) and the surface sensilla in the Geocentrophora group

“…Among six types of sensilla, described in the present study, the first (with a long thin rootlet) occurs practically in all turbellarian groups . Balloon-shaped cilia have been described in Kalyptorhynchia (see Reuter, 1975 ;Rohde et al, 1988), in Acoela (Smith & Tyler, 1985), in many parasitic platyhelminths (for references see Rohde et al, 1988), and in Gnathostomulida (Lammert, 1986) . Sensilla with a branching rootlet seem to be new for Rhabditophora ; a sensillum with three rootlets was described in Gnathostomulida by Lammert (1986), but these are three different rootlets, deriving separately from the basal body, not one rootlet branching into parts .…”

Morphology of the Turbellaria at the ultrastructural level

“…The functional significance of these structural variations in the ciliary receptors are not well understood (see Storch 1973). Rheo-, tango-and chemoreceptive functions have been most often suggested for this latter group of ciliary receptors (see Reuter 1975). Multiciliated receptors are less common, but have been noted in the Otoplanidae (see Bedini et al 1975) and in the pharynx of Haplopharynx and various macrostomids (see Doe 1981).…”

“…However, electron microscopical studies of higher pharynxtypes are generally few and restricted to the pharynx plicatus of some Tricladida (e.g. Bowen & Ryder 1973;Farnesi & Pascolini 1973;Pascolini & Gargiulo 1974;Kishida & Asai 1977) and the pharynx bulbosus of a few Rhabdocoela (Reuter 1975;Holt & Mettrick 1975).…”

Anatomy and ultrastructure of the proboscis in Mesorhynchus terminostylis (Platyhelminthes, Rhabdocoela)

“…clitellatus (see De Vocht, 1989, 1990. The receptors in the cone epithelium are present in other species as well (type IV of Reuter, 1975;Schockaert & Bedini, 1977;De Vocht, 1989, 1990.…”