Sand dollars are one of the many animals that belong to the group called Echinoderms, which includes starfish, sea urchins and other creatures.
The sand dollar is related to sea urchins but has miniaturized spines and tube feet that are more suited to sandy sea floors.
They are not endangered and are unlikely to go extinct any time soon. Their primitive nature means that they have not changed for millenia, making them highly adapted to their situation.
Current State
Sand dollars are a type of echinoderm, which are urchin-like creatures that are related to sea stars, crinoids, and sea cucumbers. They have a rigid skeleton called the test that is covered in tiny, symmetric perforations, similar to petals.
They also have ambulacral radii, or tube feet that extend from the familiar petal-like pattern on the test’s top surface, which allow them to breathe and access fresh water. They can nab food from passing currents as well.
But they are not as hardy as some other echinoderms, and their skeletal structure is vulnerable to changes in ocean chemistry and habitat loss. For example, destructive fishing practices such as bottom trawling can reduce populations of some sand dollar species.
But despite their vulnerabilities, they are not going extinct! They are currently thriving at Ocean Beach and will continue to do so as long as we keep preserving their coastal habitats. We can do our part by breeding and culturing sand dollars, instead of collecting them in the wild.
Primitive Nature
Sand dollars are a group of echinoderms that are well-adapted to live on the ocean floor. Despite their small size, they are very efficient at digesting food particles and bury themselves in the sand to protect them from predators.
Most people are familiar with their rigid outer skeleton, known as a test, that is constructed of five symmetrical calcium bicarbonate plates. These tests remain intact after the sand dollar dies and are commonly found along the shorelines of many countries.
They have radial symmetry (the bodies look the same on both sides) with the mouth and anus located at the center of the body. This is a feature that is unique to sand dollars and not seen in other urchin species.
The skeleton also has a series of small holes that allow oxygenated water to flow across its surface, allowing the animal to breathe. The sand dollar’s coat of spines also helps it move along the seabed.
Not Endangered
Sand dollars are flat, burrowing creatures that are members of the phylum Echinodermata.
They are related to radially symmetrical sea creatures such as sea lilies, sea cucumbers and starfish (also called starfish).
They are a part of the order Clypeasteroida, which contains over a hundred species worldwide.
Their skeletons, known as test, are made of fused calcareous plates which make them different from other echinoderms such as sea stars, basket stars, and brittle stars.
Their tube feet, which look like jaws on stalks, help to catch small prey and algae for food. This is done by slowly moving the animal across the sand using its spines and tiny hair-like structures, known as cilia.
Both male and female sand dollars release eggs into the water and hope for fertilization, which occurs if a suitable temperature and salinity conditions are present. Fertilized eggs hatch into larvae and grow over months, subsisting solely on plankton before metamorphosing into a fully developed adult sand dollar.
Not Going Extinct
Sand dollars are unlikely to go extinct any time soon, and are probably going to outlive humans and most other mammals on earth. They are a common part of the world’s ocean ecosystems, and are often found in shallow waters that are below the intertidal zone, where they live below the sea surface and burrow into or on top of the sand.
Scientists have discovered that 4-day old sand dollar larvae will clone themselves, in a process they use to asexually reproduce when they sense a predator’s dissolved fish mucus. This cloning process creates an exact replica that is twice as small, which helps them conceal themselves from predators.
Despite their abundance, sand dollars are facing many anthropogenic and human-based threats worldwide, such as bottom trawling, pollution, climate change, and ocean acidification. The most common threat to sand dollars is habitat loss.
