Étude du tégument et des récepteurs sensoriels du scolex d’un plérocercoïde de Cestode Tetraphyllidea à l’aide de la microscopie électronique

Abstract

Résumé.On décrit la structure des bothridies et du myzorhynque d'une larve plérocercoïde d'un Cestode Tetraphyllidea. Le tégument, au niveau de ces formations, est recouvert de microtriches de deux types. Sur la bothridie, il s'agit de microtriches lancéolés alors que sur le myzorhynque, ce sont des filaments longs et flexueux. Des récepteurs sensoriels uniciliés, présentant un ou deux colliers denses périphériques, sont observés au niveau des différents organes.Nous reprenons l'hypothèse émise par Joyeux et Baer (1961), d'une homologie entre le rostre des Cyclophyllidea et le myzorhynque des Tetraphyllidea dont nous montrons, par ailleurs, qu'il cons titue avant tout un organe de fixation. Summary.A study on the tegument and sensory receptors of the scolex of a Tetraphyllidean Cestode pleroeercoid, by transmission and scanning electron microscopy.

Sensory receptors and surface ultrastructure of trypanorhynch cestodes

“…Within the cestodes, such structures are known from Amphilinidea, Gyrocotylidea (Allison 1980;Rohde 1994), and eucestodes belonging to the Tetraphyllidea, Pseudophyllidea, Proteocephalidea, Cyclophyllidea (Gabrion and Euzet-Sicard 1979;Fairweather and Threadgold 1983;Zdarska and Nebesarova 1997;Brunanska et al 1998), and Trypanorhyncha (Davydov and Biserova 1985;Palm et al 1998;Casado et al 1999a).…”

Microtriches of tetraphyllidean metacestodes from Western Mediterranean striped dolphins (Stenella coeruleoalba)

“…In our plerocercoids, cilium-like projections occur on the apical sucker and the surface of the accessory suckers and distal bothridial loculus, three areas that contact the substratum. In other metacestodes, Gabrion and Euzet-Sicard (1979) and Casado et al (1999) described structures externally similar to the cilium-like projections of our plerocercoids, with a similar scolex distribution; based on TEM observations, these authors proposed a sensory function. In the case of merocercoids, "buttons" occur on the accessory suckers and distal bothridial loculus.…”

“…However, the possibility that the absence of microtriches is caused by a loss during the processing of the material cannot be ruled out (see Caira and Ruhnke, 1991). With respect to other tegumental structures, the external morphology of the cilium-like projections of our plerocercoids is very similar to the uniciliated sensory receptors found by Gabrion and Euzet-Sicard (1979) on the bothridial surface and the apical sucker of other tetraphyllidean plerocercoids.…”

“…Similarity also occurs in other tegumental structures; in both types, cilium-like projections appear interspersed among microtriches on several areas of the scolex. As far as is known, other tetraphyllidean plerocercoids share a similar microthrix morphology and distribution (Gabrion and Euzet-Sicard, 1979;Caira and Ruhnke, 1991;Khalil, 1995), although some differences appear to exist. Caira and Ruhnke (1991) examined several scolex regions in plerocercoids of Calliobothrium verticillatum and, unlike our results, they reported no microtriches surrounding the apical sucker.…”

“…However, information on the tegumental structures of tetraphyllidean metacestodes (the terminology for the larval cestodes follows Chervy, 2002) is rather scarce. Gabrion and Euzet-Sicard (1979) and Khalil (1995) described the morphology of several tegumental structures on the surface of unidentified tetraphyllidean plerocercoids from Mediterranean teleosts, but did not provide detailed information on the patterns of microthrix distribution. In the most detailed study to date, Caira and Ruhnke (1991) described the microtriches found on the scolex of plerocercoids and adults of the onchobothriid Calliobothrium verticillatum and revealed ontogenetic changes in the morphology and distribution of microtriches.…”