During a previous study of lithocyte transport on balancers (8), I noticed that free lithocytes, dissociated from the statolith, are often whirled or spun about by water currents under the dome (Tamm, unpubl.
Lithocytes are transported along the ciliary surface to build the statolith of ctenophores.
The single large statolith consists of numerous aggregated living cells, or lithocytes. Each lithocyte is filled with a membrane-bound calcareous concretion surrounded by a rim of cytoplasm and nucleus (Samassa, 1892; Krisch, 1973; Aronova, 1974; Tamm, 1982, 2014a, c; Noda and Tamm, 2014).
I recently discovered that the statolith of Mnemiopsis, Pleurobrachia, and Beroe is not a spherical mass of lithocytes, as previously supposed, but has a superellipsoidal shape with its major axis parallel to the tentacular plane (Fig.
The beads somewhat resembled the aggregated lithocytes of living statoliths, but were much smaller relative to statolith size.
The function of dome ciliary motility may be related to the newly discovered process of statolith formation by lithocyte transport up the balancers (see Discussion).
The relation between lithocyte supply and demand is complicated by the absence of time or age data to correlate with our morphological measurements.
I thank Signhild Tamm and the MBL Central Microscopy Facility for transmission electron microscopy, Mark Terasaki for help and support, Naoki Noda for his work on lithocyte transport, and Susan Banks for expert assistance in scanning figures.
Live cell moving on cilia: lithocyte movement on ciliary bundles during the statolith formation of ctenophore.
The single large statolith consists of an aggregate of numerous living cells (lithocytes), each filled with a large membrane-bound calcareous concretion surrounded by a thin peripheral zone of cytoplasm and the nucleus (Samassa, 1892; Krisch, 1973; Aronova, 1974; Tamm, 1982, 2014a).
It has long been known that lithocytes arise from the thickened epithelial floor of the statocyst in ctenophores (Chun, 1880; Samassa, 1892; Tamm, 1982).
This paper describes the spatial and temporal development of lithocytes, and how their novel delivery route into the statolith and the rectangular arrangement of their ciliary scaffold results in a superellipsoidal shape and a specific orientation of the statolith.