Paranephelium xestophyllum is one of two Paranephelium species that occur in Borneo. Paranephilum are in the Rambutan family (Sapindaceae) and these two species are very similar in appearance to the Horsechestnuts (Aeschalus) of Europe and N. Asia, also in the Sapindaceae. As with Aeschalus there is no aril (edible pulp) attached to the seed, therefore dispersal by primates is extremely unlikely.
The Horsechestnuts (Aeschalus) are dispersed in two ways. Large browsers e.g. elephants, deer, pluck the fruits hanging from small trees when they are ripe to swallow the pericarp and defecate the seed. If the shiny seeds fall directly to the ground they are collected and scatter-hoarded or larder-hoarded by rodents e.g. rats or squirrels.
According to Glyn Davies who studied Red Langur feeding ecology at Sepilok Red Langurs (Presbytis rubicunda), the diet consisted largely of young leaves and unripe fruit and seeds especially seeds without any sweet pulp (aril) surrounding the seed. Thus Red Langurs were seed predators of Paranephilium seeds.
Davies (1991) Seed eating by Maroon Langurs
For further information on the two Paranephelium species in Borneo see;
Davids (1984) Taxonomic revision of Paranepheliulm (Sapindaceae) BLUM1984029002008