Sexual dimorphism in the parasitic snail Nanobalcis worsfoldi: a histological and morphometric approach with insights for the family Eulimidae

Sexual dimorphism has long been stressed as a remarkable characteristic of Eulimidae snails. This idea is so common for this family that, even without information on the soft parts, some species were already identified as male or female, as observed in Nanobalcis worsfoldi Waren, 1990. Here, we investigated whether larger and smaller individuals of N. worsfoldi are female and male, respectively, and what are the most useful characteristics to differentiate the sexes. We analyzed shell morphology and morphometry, along with coloration of the soft parts of large and small individuals, and crosschecked our findings through histological analysis. Our results confirmed that (i) larger and smaller individuals are females and males, respectively; (ii) shell morphology is not useful, while morphometry is important to address sexual dimorphism; (iii) since shell length and width showed the most remarkable differences, they are considered the best parameters to predict the sex. Furthermore, conchological characteristics associated with histological analysis suggest that this species could be the first non-sessile eulimid known as a sequential hermaphrodite (protandric) with environmental sex determination, but this remains to be confirmed. Considering that most studies on eulimids are based on shells, the morphometric parameters used here may support future ecological/biological analyses in the family, such as parasitological prevalence, or parasitic burden related to sex.