Sentence:  They do not always elevate their polyparies from the depths of the waters to their surface, some extend themselves horizontally upon the bottom of the sea, following its curvatures, declivities, and <WSD>anfractuosities</WSD>, and cover the soil of old ocean with an enamelled carpet of various and brilliant colours, sometimes of a single colour as dazzling as the purple of the ancients. 
Meaning of the word marked with <WSD> tags:  A winding channel or crevice, such as occur in the depths of the sea or in mountains.