Sclerodermite

In fact each zoonite in turn is formed of several distinct parts or sclerodermites, which also, by welding together, produce arrests of development and atrophied members.

The most recent study has been made by Hayasi (78), who finds that the calcareous lamellae which form the sclerodermites are formed by secretions of the calicoblasts and that the latter are not themselves calcified.

The same is true of the sclerodermites of Holothuroidea but it is not true of other echinoderm microfossils, such as echinoid pedicellariæ and microcrinoids.

Where the sclerodermites are arranged in a linear series making an almost continuous ( commonly zig-zag, Fig.38) line of centres of calcification, the resulting trabecula has a circular cross-section equal to the equatorial section of a single sclerodermite.

Observations made during microprobe analysis and with SEM indicate that calcitized sclerodermite centers are concentrated in horizons parallel to growth banding.

The aspicular, aragonitic skeleton of a living sphictozoid (Neocoelia) lacks the sclerodermite microstructure in other aragonitic skeletons indicating a significant difference in the pattern of crystallization. The absence of entrapped siliceous spicules in this sponge does not appear to be the cause for the lack of sclerodermites since in Merlia sclerodermites are present but entrapped spicules are not ( Hartman and Goreau, 1970).