''Zoosphaerium neptunus'', also known as the giant emerald pill millipede, is a species of millipede within the family

Arthrosphaeridae Arthrosphaeridae is a family (biology), family of Sphaerotheriida, giant pill millipedes that are found in Madagascar, the Western Ghats of India, and Sri Lanka. The largest pill-millipede in the world, ''Zoosphaerium neptunus'' (Butler 1872) bel ...

. Its size is an example of

island gigantism Island gigantism, or insular gigantism, is a biological phenomenon in which the size of an animal species isolated on an island increases dramatically in comparison to its mainland relatives. Island gigantism is one aspect of the more general "is ...

, it being the largest known pill-millipede in the world, with some individuals reaching a maximum length of 90 mm (3.5 inches) long. The species is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

, where it is known to swarm at certain times of the year. ''Z. neptunus'' is the only known species within the order

Sphaerotheriida Sphaerotheriida is an order (biology), order of millipedes in the infraclass Pentazonia, sometimes known as giant pill millipedes. They inhabit Southern Africa, Madagascar, South and Southeast Asia, Australia and New Zealand. Like the Northern He ...

that is known to exhibit this mass swarming behaviour.

Description

''Zoosphaerium neptunus'' is a large species of pill millipede which ranges in colour from a shiny light green to a darker olive green. The species is characterized by smooth and hairless tergites. The tergites display a green coloration, with a thin brown line along the posterior margin. The head possesses over 80

ocelli A simple eye or ocellus (sometimes called a pigment pit) is a form of eye or an optical arrangement which has a single lens without the sort of elaborate retina that occurs in most vertebrates. These eyes are called "simple" to distinguish the ...

, and the antennae consist of six joints. The sixth joint is the longest, and it bears a disc with 18-26 sensory cones on the tip. The first segment has long isolated hairs along its anterior margin and a row of even more strongly isolated hairs along the posterior margin. The legs exhibit varying numbers of ventral spines on different tarsi.Wesener, Thomas & Wägele, J. Wolfgang. (2008). The giant pill-millipedes of Madagascar: Revision of the genus Zoosphaerium (Myriapoda, Diplopoda, Sphaerotheriida).

Zoosystema ''Zoosystema'' is a peer-reviewed scientific journal published by the National Museum of Natural History, France (''Muséum national d'histoire naturelle''), covering research in animal biodiversity. Specific subjects within the journal's scope in ...

. 30. 5-85.

Sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

is present within the species, with females reaching larger sizes than males. Males reach up to around 45 mm (1.8 inches) long, while females can reach up to 90 mm (3.5 inches) long. Preserved specimens may darken in alcohol, becoming light brown.

Male traits

Hands full of rolled up Zoosphaerium neptunus

Males have an average length of 45.5 mm, the width of the thoracic shield is 21.5 mm, and a height of the thoracic shield is 11.35 mm. The mandible possesses six rows of pectinate lamellae, and the gnathochilarium has numerous bristles. The tergites of males are smooth and hairless with green coloration. The anal shield in males is strongly bell-shaped and covered laterally with numerous small round pits, some of which support a short hair. The legs have weakly curved claws on the first two leg pairs and tarsi that are 4.6 times longer than wide, with curved claws and 8-10 ventral spines. The anterior telopods, used for reproduction, possess a stridulation harp and one stridulation rib on the first joint, with a process on the second joint reaching about half to three-fifths of the third joint's height. The posterior telopods have a slimmer third joint towards the tip and a chela covered with isolated long hairs on the posterior side.

Female traits

Females can reach an average length of around 80.9 mm and a width of 45.85 mm. The vulva of females is large, covering more than two-thirds of the coxa. The operculum is elongated, protruding up to the apical edge of the coxa, with an apical margin that is notched and two rounded tips. The subanal plate in females has a washboard-like structure consisting of well-developed stridulation ribs, with 2-3 ribs on each side. The anal shield in females is weakly bell-shaped and covered laterally with numerous small round pits. Females have tarsi that are 4.6 times longer than wide, with curved claws, 8-10 ventral spines, and one apical spine. The stigma-carrying plates in females consist of a short lobe covered with long hairs and curved towards the coxa.

Distribution and habitat

''Zoosphaerium neptunus'' is an endemic species found only in Madagascar where it is widely distributed on the island. ''Z. neptunus'' can be found living among leaf litter in moist lowland

rainforest Rainforests are forests characterized by a closed and continuous tree Canopy (biology), canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforests can be generally classified as tropi ...

habitats up to elevations of 850 metres above sea level. ''Z. neptunus'' is a detritovore, which feeds on decaying organic matter such as rotten wood and dead leaves.

Pet trade

''Zoosphaerium neptunus'' is vulnerable to collection for the

pet trade Wildlife trade refers to the exchange of products derived from non-domesticated animals or plants usually extracted from their natural environment or raised under controlled conditions. It can involve the trade of living or dead individuals, tis ...

. Captive populations tend to have a scarcity of males, possibly because their smaller size renders them less desirable to collectors compared to the larger females. The species is known to have a short lifespan in captivity, often starving to death due to conditions incompatible with its regionally-specific metabolic adaptations.

References

{{Taxonbar, from=Q27941374 Sphaerotheriida Endemic fauna of Madagascar Arthropods of Madagascar Millipedes of Africa Animals described in 1872