The skeleton is responsive to mechanical usage (immobility means significant atrophy), yet the basis for its remarkable sensitivity remains uncertain. Osteocytes seem central as they are the most abundant bone cells (90%). Their cytoplasmic syncitium is pervasive and well placed to bridge the uncertain gap between mechanical signal transduction and cellular response especially since it is morphologically reminiscent of a neuronal network. However, its calcified entombment limits accessibility, while isolation or manipulation may alter its specific threshold characteristics. Insight into the basics of musculoskeletal exchange may be found in certain protozoa from which the metazoan pathway apparently evolved (Pautard, 1960, 1970; Ruffalo, 1978). In particular is the organism Spirostomum ambiguum (a cigar-shaped creature visible to the naked eye) which fabricates and accumulates calcium phosphate particles, about 1µm in diameter, resembling those in bone. Moreover, their intracellular, golgi-directed synthesis (Fallon and Aaron, in press) is determined by the active life-cycle of the animal. This modulates between a free-swimming state when calcified particles are minimal and a silt-burrowing stage when calcified particles become abundant. Thus when the mineral of cultured S. ambiguum was labelled with the fluorochrome tetracycline (commonly used as a bone histology marker of formation) the green fluorescence intensity (AU) mapped using laser confocal microscopy, recorded a high mineral level in the silt-burrowing animals (138.0 ± SD4.0) compared with their free-swimming counterparts (89.7 ± SD 3.3). Similarly when the live organisms were transfected with a GFP construct (Fallon, 2006) the resulting GFP-tagged mannosidase II enzyme as an expression of Golgi activity differed significantly (p<0.0001, two-sample t-test) between tunnelling (104.6 ± SD 2.7) and free-swimming (74.5 ± 6.7) activity. Within the same context, it was observed that the distribution of the intracellular particles did not seem to be entirely random. Rather, a proportion related in disposition to a regular and well-defined pattern of contractile muscle myonemes, the fibres of which were arranged longitudinally within the high stress burrowers in contrast to their transverse alignment in the low stress swimmers. The capacity of this animal model not only to package bone-like mineral in response to changing environmental pressures, but also to relate them to their intracellular contractile elements may suggest an early integrated musculoskeletal system and cytoplasmic calcium phosphate storage phenomenon that substantially predated the vertebrates which eventually exploited the major advantages they bestowed. The apparently modest protozoan model described may therefore serve as a valuable tool for future fundamental investigation of osteocyte ancestry, mechanotransduction, perception and response.