Below: Seen upside down here, this pedicle (lower) valve of Actinoconchus shows the expansions along the growth lines, but the fine ribbing is not clearly visible in this specimen.
These layered expansions helped to prevent Actinoconchus sinking into the muddy sea floor it inhabited, and also acted as camouflage, protecting it from the attentions of predators.
These creatures fed by filtering out tiny
particles of food from the surrounding water