Heliophora orbicularis, also known as the West African Sand Dollar, is a small sand dollar in to the family Rotulidae, and the only species in the genus Heliophora. It, and other members of Rotulidae have been found in West African marine strata from the Late Miocene onward. Like the related , it is still extant. Description Individuals of H. orbicularis are very distinctive in appearance and also highly morphic, with a remarkable diversity in individual specimens. This genus has an extremely variable circular to oval-shaped test. The indentations may remain restricted to the posterior edge or may be found along the entire margin of the test. The indentations may be very shallow or quite deep, forming long "fingers," or digits. The digits are very fragile, and prone to breaking off. Ecology and feeding Heliophora orbicularis live in large groups in very shallow water of lagoons and estuaries, usually lightly buried in mud. Food particles are picked out of the substrate by the tube feet, and are maneuvered into the food grooves along the oral side of the test, which are underneath the digits of the test. Once placed into a food groove, food particles are caught in a string of mucus and moved into the mouth, which is located in the very center of the oral side of the test. Distribution This sand dollar is present from western coast of Sahara and Senegal to Angola. Morphology Within a group of organisms, taxa showing morphological extremes are favorite objects in constructional morphology, and the West African Sand Dollar is no exception. The West African Sand Dollar is a bilaterian (animals with bilateral symmetry) even though adults possess radial symmetry, because the larvae possess bilateral symmetry. Since the organism is a bilaterian, it has three tissue layers: endoderm, ectoderm, and mesoderm. The sand dollar is part of the phylum Echinodermata, and so the organism has an endoskeleton composed of calcareous ossicles which grow from the mesodermal tissue. This endoskeleton is covered in ciliated tissue. The West African Sand Dollar is a deuterostome, meaning that the blastopore forms an anus instead of the mouth. The organism has an oral surface with podia (tube feet) and ambulacral grooves and an aboral surface. These tube feet are not used for locomotion in sand dollars, but instead for gas exchange. Instead, locomotion is achieved by movable spines. In the center of the test, the West African