Terga

Definition and stakes

Portrait of Charles Darwin Charles Darwin,  A Monograph on the Sub-class Cirripedia…

“ The Terga are remarkable for their variability in all the species; in many specimens of E. Kingii and modestus the basal margin on the carinal side of the spur is deeply hollowed out. The width and acumination of the spur varies in all the species. In E. plicatus and simplex this valve is remarkably like that of Tetraclita porosa. In some specimens of E. Kingii the terga and scuta are firmly calcified together.
Structure of the Parietes and Radii.—As in Tetraclita, the two lateral compartments are necessarily broad.
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Source: Gutenberg

Portrait of Charles Darwin Charles Darwin,  A Monograph on the Sub-class Cirripedia…

“ Terga, with the apex beaked, beak triangular, dull purple; the longitudinal furrow is so shallow as hardly to exist. The basal margin slopes down on both sides, with a nearly equable curvature towards the spur; hence the spur is broad in its upper part, and narrow at its obliquely truncated lower end. Internally, there is an elongated dark purple patch: the shallow articular furrow is of quite remarkable breadth; the articular ridge is medial, and the inflected scutal margin is not wide. ”
Source: Gutenberg

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