Heliophora

Lore & Background

Heliophora orbicularis is highly morphic, with a remarkable diversity in individual specimens. Its test is extremely variable, ranging from circular to oval, and may have indentations restricted to the posterior edge or found along the entire margin. These indentations can be very shallow or quite deep, forming long fragile digits that are prone to breaking off. The species lives in large groups in very shallow lagoons and estuaries, usually lightly buried in mud. Food particles are picked from the substrate by tube feet and moved into food grooves on the oral side, then caught in a string of mucus and transported to the mouth at the center of the test.

Reader's Guide

Heliophora is significant as the sole member of its genus and as a subject of constructional morphology due to its morphological extremes. Like other sand dollars, it possesses an endoskeleton of calcareous ossicles, an Aristotle's lantern for feeding, and lunules that reduce lift generated by its low domed profile on unstable sediments. Its spines are adapted for burrowing and feeding rather than protection. The species is capable of delaying metamorphosis for a limited time, a trait studied in related sand dollars; research indicates that spontaneous metamorphosis peaks in the fourth week of competence and that juvenile growth is faster when sand is present. This adaptation may help larvae avoid tube-building predators such as Leptochelia dubia.

Did You Know?

• Heliophora orbicularis is the only species in the genus Heliophora.
• Its digits are very fragile and prone to breaking off.
• The species lives in large groups in very shallow water of lagoons and estuaries.
• It is capable of delaying metamorphosis for a limited amount of time.