at Roscoff But proliferated when oil covered the sea in English Channel - lack of light, lack of sediment. Spine forms simply by upward projection of epithelial cells. The speciality of spines i.e. are there different kinds is a separate question in G.'s thinking A spine Epithelial cells always come together - you can't keep them apart; they always have a binding action. always some undiff. cells wh. have potential as embryonic cells to take off as growing tip.