Qualitative and quantitative insights into the 3D microanatomy of the nervous ganglia of Scrobicularia plana (Bivalvia: Tellinoidea: Semelidae)

ABSTRACT

The nervous system of bivalves is bilaterally symmetrical and consists of interconnected cerebropleural, pedal and visceral ganglia, which may be partially to totally fused. We studied the microanatomy of the ganglia of Scrobicularia plana using three-dimensional (3D) reconstruction. We also examined whether intersex differences in the neural structure exist. Each type of ganglion had a characteristic 3D shape, and the cerebropleural ganglia shape was slightly asymmetrical. The visceral, pedal and cerebropleural ganglia are progressively smaller in volume, but only the pedal ganglion volume was positively correlated with the animal’s length, height or width; suggesting functional implications. As to total surface area, correlations were found for the cerebropleural and visceral ganglia, but it was the visceral that consistently showed strong positive correlations with each biometric parameter. The medulla may often penetrate the cortex and touch the capsule in areas that (contrary to what might be expected) are not connected with emerging nerves. Despite the differences in volume and surface area among ganglia, the volume ratio of cortex/medulla is fairly stable (c. 1.5), suggesting a functional optimum. Finally, we conclude that the ganglia of males and females do not show significant quantitative differences.

KEYWORDS:

• Bivalve
• histology
• morphometry
• nervous system
• 3D reconstruction

Acknowledgements

We thank Fernanda Malhão and Célia Lopes for teaching technical details to the first author, and for overseeing her in the processing of the animals for histology. We also thank Catarina Cruzeiro for helping in bivalve handling in the field and in-house. We are grateful for the editorial advice that improved the manuscript.

ORCID

Eduardo Rocha http://orcid.org/0000-0001-9813-4389

Additional information

Funding

The first author was supported by a Thai Government Science and Technology Scholarship. This work was partially supported by funds from the European Regional Development Fund (ERDF) through the Competitiveness and Trade Expansion Program (COMPETE) and by national funds as provided by the Fundação para a Ciência e a Tecnologia—FCT, via the research project PEst-C/MAR/LA0015/2013 and the strategic funding UID/Multi/04423/2013.