Ultrastructure of gametogenesis in the ovotestis of an estuarine pulmonate slug, Onchidium tigrinum (Stoliczka, 1869)

ABSTRACT

The pulmonate slug Onchidium tigrinum (Stoliczka, 1869) is an estuarine protandrous gastropod. Transmission electron microscopy of both the gonadal and somatic cell populations of the ovotestis of the slug is documented. The acini of smaller slugs are comprised of developing spermatogenic cells and three to four small ill-developed oocytes. Details of the microscopic structures of Sertoli cells, interacinar cells and acinar boundary are described in-depth, revealing their secretory function. Sertoli cells are more numerous in the ovotestes of smaller slugs than in those of larger slugs. Tunnelling nanotubes of 200–400 nm in diameter are described for the first time in the Sertoli cells of molluscan ovotestis. These nanotubes may help to supply various cellular materials into distantly developing spermatogenic cells. The acini of larger slugs possess 2–3 mature oocytes along with a few spermatogenic cells. Sertoli cells, interacinar cells and spermatogonial cells are fewer in number in the acini of the ovotestis of larger individuals establishing the predominance of oogenesis in this phase of life. The number of oocytes per acinus is analysed in relation to the habitat of the pulmonates.

KEYWORDS:

• Follicle cell
• hermaphrodite
• interacinar cell
• periacinar cell
• tunnelling nanotube

Acknowledgements

The authors express their thanks to the laboratory staff of the Department of Zoology, City College, Kolkata for their necessary help in light microscope observations and to the staff of the TEM unit, Department of Anatomy, AIIMS, New Delhi for their technical support and photographic services. The authors express their thanks to Dr A. Dey, Zoological Survey of India, Kolkata, West Bengal for the identification of the slugs. The authors also express their acknowledgments to Dr Gary Barker, Associate Editor and an anonymous reviewer for their constructive suggestions on the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Soumen Roy http://orcid.org/0000-0002-3510-0947

Korak Kanti Chaki http://orcid.org/0000-0003-1681-9718

Tapas Chandra Nag http://orcid.org/0000-0002-6962-0844

Kamales Kumar Misra http://orcid.org/0000-0003-4909-3319