STRUCTURE AND NOVEL BIOMINERALIZATION OF MNEMIOPSIS LEIDYI AND BEROE OVATA LITHOCYTE CONCRETIONS (LCS) AS REVEALED BY POLARIZATION (LC-POL), SCANNING ELECTRON MICROSCOPY (SEM) AND ELECTRON DISPERSION SPECTROSCOPY (EDS)

Ctenophore statocysts have multicellular statoliths borne on the tips of balancer compound cilia (Curr. Biol. 24:R951; Biol. Bull. 227:7). Lithocyte concretions (LCs) were prepared by three methods: 1) statocysts were microsurgically collected and washed w/0.2 µm filtered sea water (FSW), followed by 5 diH₂O rinses in a deep well dish (DWD); 2) statocysts were treated with 50% Chlorox/FSW to release the statolith/LCs; 3) statocysts were fixed in 2.5% glutaraldehyde or 1% paraformaldehyde-2.5% glutaraldehyde in 10 mM pH 7.8 HEPES-buffered FSW, and statoliths and LCs microsurgically released. LCs for SEM were glued to stubs, C-stabilized and Pt-coated to a thickness of 8 nm and viewed at 10 kVe. LCs for EDS were applied to carbon tape on aluminum stubs and analyzed by EDS at 3 and 10 kVe. SEM and EDS were performed on a Zeiss Supra 40 VP equipped with an EDS detector controlled by INCA software (Oxford). Results were compared against compounds of known elemental composition. LCs examined by LC-POL revealed no birefringence (BR). LCs viewed by SEM were either a lumpy mass (M. leidyi) or smooth ellipsoid (B. ovata). LCs on carbon tape typically shattered and released overlapping, layered, multi-oriented crystals. EDS of LC crystals from both species collected by all methods lacked Ca, Mn and Mg. Predominant elements were Na, K, O and S in ratios suggesting that LCs contain mixed sodium/potassium sulfates. The unique composition of ctenophore statoliths may have been critical for the 600+ million years persistence of these organisms (J. exp. Biol. 218:592) including survival through multiple global extinctions and related ocean acidifications. Thanks to L. Kerr, R. Oldenbourg, S. Mehta, A. Verma, M. Tran, A. Kuzirian and S. Tamm for stimulating discussion and technical advice. EDS stds compounds were curtesy of L. Amaral-Zettler, J. Huber and K. Gribble (Bay Paul Center/MBL). Funding: AU PIL Program, NSF-EPS-1158862.