Chaetotaxy and ultrastructure of sensory receptors in the cercaria of a species of Allassogonoporus Olivier, 1938 (Digenea:Lecithodendriidae)

Abstract

A standard procedure that combines chaetotaxic, ultrastructural and neuromorphological observations has recently provided a new perspective to the study of cercarial sensory systems. In the present work, we aimed to extend the use of this combination of techniques to investigate the chaetotaxy of Allassogonoporus sp. in conjunction with the ultrastructure of sensory receptors and neuromorphology. Five nerve regions were distinguished. A conspicuous bilobed cerebral ganglion was observed at the level of the pharynx. The chaetotaxic pattern was generally consistent with that of other lecithodendriids. Four types of receptors were distinguished with scanning electron microscopy. These types differed in cilium length (short, moderately long or long) and tegumentary collar length (moderately low or high). Internal ultrastructure of receptor type IIAL revealed an unsheathed cilium, a closed basal body, septate extracellular junctional complexes and thickened nerve collars. Some receptor types were site-specific. Long uniciliated receptors were found mainly on the dorsal surface, whereas short uniciliated receptors were widespread across the tegument. Ultrastructure and site-specificity observations suggest that most sensory receptors are mechanoreceptors, probably reflecting the important role mechanoreception plays in host finding.

Topography and ultrastructure of the tegument of Lecithochirium musculus (digenea: Hemiuridae), a parasite of the European eel Anguilla anguilla (osteichthyes: Anguillidae)

“…The homogeneous distribution of the two types of sensory receptors in L. musculus may indicate site‐specificity in the distribution of these receptors. Site‐specificity in the distribution of sensory receptors has also been reported in other digenean species (Bogea and Caira,2001; Abdul‐Salam and Sreelatha,2004; Mata‐López and Leon‐Regagnon,2006). Most of the receptors are concentrated in the anterior third of the fluke, which contains oral and ventral suckers.…”

“…Among Digenea, studies on tegumental sensory structures have mainly focused on cercaria or metacercaria stages (Fujino et al,1979b; Matthews and Matthews,1988a; Žd'árská,1992; Bogea and Caira,2001; Abdul‐Salam and Sreelatha,2004; Poddubnaya et al,2010) as they require orientation to stimuli such as light and gravity more than adults do, a condition related to the necessity of finding a host quickly (Roberts and Janovy,2000). However, some authors have emphasized the description of tegumental structures of adult digeneans (Žd'árská,1993; Ferrer et al,1996; Ibraheem,2000; Filippi et al,2010).…”

New data on the nervous system ofCercaria parvicaudataStunkard & Shaw, 1931 (Trematoda: Renicolidae): revisiting old hypotheses

“…Based on these data it is possible to suggest the role of the individual receptor (Žd’árská & Nebesářová, 2003; Antonelli et al ., 2014). It is assumed that receptors with long cilia respond to low mechanical stimuli, such as water currents, and are localized on the dorsal surface (Bogéa & Caira, 2001, 2001b), especially in A D groups (fig. 3e, g).…”

“…Sensory papillae with short cilia and a high tegumental collar are more often located on the ventral surface (figs 1f and 2d, c, f), which is directly in contact with the substrate. The tegumental collar is considered important for tactile mechanoreception (Bogéa & Caira, 2001).…”

“…Sensory papillae of C. parvicaudata are mainly represented by uniciliate nerve endings surrounded by the tegumental collars (figs 1–3). This type of papillae is common among both cercariae and adults of various digenean families (Bogéa & Caira, 2001, 2001a, b; Sohn et al ., 2002; Žd’árská & Nebesářová, 2003; Antonelli et al ., 2014). The sensory endings of the oral sucker of C. parvicaudata are also of the same type (fig.…”