The fine structure of gametogenesis and somatic cells in the ovotestis of the terrestrial pulmonate slug, Laevicaulis alte (Férussac, 1822)

ABSTRACT

The development of gametes and somatic cells in the ovotestis of Laevicaulis alte of different body weights is studied using transmission electron microscopy. Spermatogenesis is a proliferative phase in the ovotestis of smaller slugs acting as males, while oogenesis predominantly occurs in larger slugs acting as females. Male gametes are distributed throughout the acini in smaller slugs and residual cytoplasmic materials of developing spermatids bud off into the Sertoli cells. In larger slugs, each acinus comprises only one vitellogenic oocyte, completely surrounded by a follicle cell layer with a follicular cleft which is linked to the development of the oocyte. Oocytes utilise auto- and heterosynthetic mechanisms of yolk formation. Autosynthesis is accomplished by various ooplasmic organelles while heterosynthesis is promoted by an endocytic activity of the oolemma. The development of gonadal somatic cells is directly related to the growth of stage-specific gametogenesis. Sertoli cells are divided for the first time into two categories, cortical Sertoli cells or luminal Sertoli cells. Sertoli cells possess numerous tunnelling nanotubes which assist the transportation of cellular components to distant developing gametes. The suggestion that oocyte numbers in each acinus depend more on the corresponding habitats of the pulmonate species than on their taxonomic relatedness is discussed.

KEYWORDS:

• Follicular layer
• hermaphrodite
• interacinar cell
• periacinar cell layer
• tunnelling nanotubes
• types of Sertoli cell
• ultrastructure
• yolk formation

Acknowledgments

The authors express their thanks to the Department of Zoology, City College, Kolkata for their necessary help in light microscopic study and to the staff of TEM unit, Department of Anatomy, AIIMS New Delhi for their technical support and photographic services. The authors thank Dr. Amit Mukherjee and all other faculty members, Mollusca Section, Zoological Survey of India, India, for identification of specimens. The authors also express their thanks to the Head of the Department of Zoology and other faculty members of West Bengal State University, Barasat, West Bengal, India. The authors are also grateful to the reviewers of the manuscript for their constructive suggestions.

Disclosure statement

No potential conflict of interest was reported by the authors.