Brachiopod Similarities And Differences

All animals belong to the supergroup Unikonta. Since these animals are found in almost every environment on earth, it has become possible to study their characteristics and construct evolutionary relationships, noting morphological and molecular similarities and differences. The relationships between the most primitive of animals were determined by the morphological traits of symmetry, tissues, body cavity, embryological development, and molecular evidence. [1] Symmetry and tissues are major determinants in the differentiation of clades. Ancestral forms exhibit no symmetry and no tissue. Over time, radial symmetry arose along with diploblastic tissue followed by bilateral symmetry with triploblastic tissues. [2] Symmetry and tissue are the …show more content…
[3] Additionally the two classes of Brachiopoda, Inarticulata and Articulata, are differentiated by their hinges. Inarticulata, the more primitive of Brachiopoda, possess a simple, smooth hinged while the Articulata class have a complex, teethed hinge. Despite their differences in hinges, all Brachiopods have a mantle, a trait which is shared with the phylum Mollusca. Mollusca can be differentiated from the rest of the supergroup Unikonta by the presence of a foot. The foot, a modified appendage which offers anchorage and locomotive abilities, is found in all four classes of Molluscs, Cephalopoda, Gastropoda, Polyplacophora, and Bivalvia. The foot of a Cephalopod however, bears little resemblance to the foot of the other three classes. Instead, the Cephalopod foot bears arms and tentacles which offer jet propulsion. [4] To differentiate among the three remaining classes, Polyplacophora have dorsal plates, Bivalvia have a calcium carbonate two valve shell, and Gastropoda possess the distinctive characteristic of torsion, the ability of the internal organs to rotate 180° within the