Ultrastructure of the anterior organ and posterior funnel-shaped canal of Gyrocotyle urna Wagener, 1852 (Cestoda: Gyrocotylidea).

Larisa G Poddubnaya,Tomas Scholz,Roman Kuchta,Glenn A Bristow

doi:10.14411/fp.2015.027

Larisa G Poddubnaya, Tomas Scholz + Show 2 more

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https://doi.org/10.14411/fp.2015.027

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Abstract

Using scanning and transmission electron microscopy, ultrastructure of the anterior organ and posterior funnel-shaped canal of Gyrocotyle urna Wagener, 1852 (Cestoda: Gyrocotylidea) from ratfish, Chimaera monstrosa (Holocephali), was studied for the first time. The proper anterior organ is localised at a short distance (about 170 µm) from an apical pore surrounded by a receptor field, whereas its distal end is marked by a muscular sphincter. The tegumental surface of this organ is covered with short filitriches of irregular length; large area of muscle layers traverse beneath the tegumental layer. The funnel-shaped canal of G. urna (2.5-3.0 mm long) is a specialised, muscular part of the posterior attachment organ; it opens on the rounded elevation on the dorsal body surface. The tegumental layer bears conical sclerite-like structures (up to 1.5 µm long). It produces electron-dense bodies that are transported into a canal lumen and surrounded thick muscle area mixed with numerous nerve fibres. The present ultrastructural study of G. urna indicates that gyrocotylideans share some ultrastructural characters of the anterior organ with spathebothriidean cestodes with a single anterior attachment sucker-like organ. In contrast, the unique posterior rosette attachment organ with funnel-shaped canal of the Gyrocotylidea resembles the haptor of polyopisthocotylean monogeneans in its position at the posterior end of the body and presumed origin. The above-mentioned features add more clarity to support the basal position of the Gyrocotylidea Poche, 1926 among cestodes. In addition, they also indicate a possible relationship of gyrocotylidean ancestors with monogeneans.

Highlights

The Gyrocotylidea Poche, 1926 are a small and enigmatic group of unsegmented cestodes (Cestoda), which includes 10 nominal species that are parasites of ratfishes belonging to an ancient vertebrate group, the Holocephali (Bandoni and Brooks 1987, Williams et al 1987, Bristow 1992, Gibson 1994)
The aim of the present study is to provide data on the ultrastructure of the anterior organ at the anterior end and the funnel-shaped canal of the posterior attachment organ of Gyrocotyle urna Wagener, 1852
Anterior organ of Gyrocotyle urna scanning electron microscopical (SEM) micrographs of Gyrocotyle urna show that its anterior extremity can be slightly extended over the body and is pierced by a circular opening into the cavity of the anterior organ (Fig. 1A,C)

Summary

Introduction

The Gyrocotylidea Poche, 1926 are a small and enigmatic group of unsegmented cestodes (Cestoda), which includes 10 nominal species that are parasites of ratfishes ( known as chimaeras) belonging to an ancient vertebrate group, the Holocephali (Bandoni and Brooks 1987, Williams et al 1987, Bristow 1992, Gibson 1994). (1985) compared this invagination with the mouth (oral sucker) of monogeneans, testifying to the ancestral presence of a digestive system and considering this structure as muscular organ; they illustrated this organ as a sucker for 10 species of Gyrocotyle Wagener, 1852 (see Bandoni and Brooks 1987). The posterior rosette of gyrocotylideans serves for their fixation in the spiral valve of the final (definitive) hosts (Williams et al 1987), a conspicuous difference from other cestodes where the attachment organs are situated at the anterior extremity of the body (scolex).

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