Zoosphaerium neptunus is an endemic Malagasy species (restricted to Madagascar). It exhibits a relatively widespread distribution throughout the island. Specimens of this millipede are typically found inhabiting the leaf litter of humid tropical lowland forests, with an altitudinal range extending up to 850 meters above sea level (m a.s.l.).
Zoosphaerium neptunus belongs to the Class Diplopoda (millipedes), Family Arthrosphaeridae. Like all congeners, it possesses a robust chitinous cuticle and a segmented body plan. Each segment, beginning with the fourth, bears two pairs of legs (the first segment is legless, while the following three each possess a single pair). These organisms exhibit a dark green, emerald coloration. Females reach a maximum length of 90 mm, while males grow up to 45 mm. When threatened, the individual performs volvation, rolling into a tight sphere. The margins of the plates covering the animal’s body (tergites) coincide perfectly, resulting in a highly hermetically sealed ball.
Zoosphaerium neptunus millipedes possess an additional notable trait: they live in large aggregations. This colonial behavior is hypothesized to provide enhanced anti-predator defense.
These individuals are detritivores, feeding on decomposing leaves, wood, and fungi. It is posited that their gut microbiota includes bacteria capable of lignin degradation. Thus, by breaking down organic matter and facilitating its return to the soil, they perform a critical function in nutrient cycling within their ecosystem.
Following fertilization, Zoosphaerium neptunus females deposit their eggs into crevices, specifically within the layer of decaying leaves. After several weeks, the juvenile millipedes hatch. These initial instars are morphologically similar to a comma and possess three pairs of legs. As they grow, they undergo ecdysis (moulting), with the number of legs increasing after each subsequent moult.
There is interest in keeping these millipedes in captivity; however, attempts are often unsuccessful. This failure is typically attributed to the millipedes rejecting the food offered by keepers, leading to starvation. Collection of this species is prohibited in Madagascar, yet illegal harvesting activities persist.
