Rio History: Tests of Heart Urchins

By STEVE HATHCOCK
Special to the PRESS

Pete Stathis asked me to help identify some interesting shells he found while beach combing on South Padre Island.

Here is my answer.

Hi Pete, congratulations on your rather rare find. However, these are not shells … rather these are the remains of a broad group known as echinoderm which are closely related to the common sand dollar. In echinoids, the skeleton is almost always made up of tightly interlocking plates that form a rigid structure or test. The shape of the test can be either flattened or globular shaped. Living echinoids are covered with spines, which are movable and anchored in sockets in the test. In sand dollars and heart urchins the spines are very short and form an almost felt-like covering. The mouth of most echinoids has five hard teeth arranged in a circlet known as Aristotle’s Lantern.

Heart urchins, also known as mud urchins, can reach a size of nearly 2 inches in diameter. They are light brown to yellow-brown, and in many specimens, a horseshoe-shaped line of dark red pigmentation partially encircles the central area of the test. Heart urchins are found primarily on mud or muddy-sand substrates where they may burrow to a depth of 6 inches. They feed on various types of organic matter, including plants, small animals, and waste material. Heart urchins can be found along most areas of the Atlantic and Gulf Coast. They are found at depths ranging from zero to 1,500 feet, but are most common at depths less than 160 feet.

Be careful when handling any urchin. Both the long-spine purple urchin and the short-spined urchin, found locally, are covered with sharp, venom-coated spines. Touching or stepping on these spines can produce a painful puncture wound. The spines commonly break off in the skin. If they are not removed immediately they can cause joint, muscle pain and skin rashes. Vinegar dissolves most sea urchin spines and several vinegar soaks or compresses may be all that is needed to remove spines that have not penetrated deeply. If vinegar is not available, soak the area in hot water as heat will inactivate urchin venom. It’s a good idea to visit a doctor if the spines break off in your skin.

Thanks for the photos!

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