Sand Dollars | Learn About Their Decorative Use

Sand Dollars

What Is A Sand Dollar?

Sand dollars are a type of marine invertebrate that lives in warm coastal waters and sands on the ocean floor. They feed on microscopic plants and animals, which they strain from the sand they pass through their feeding apparatus.

Their skeletons are composed of individual calcite elements called ossicles (a tiny skeletal element fused together), each one shaped like a miniature sand dollar. These ossicles are embedded in the skin, connected by soft tissues.

The skeletons of these urchins typically disintegrate after the death of the animal, but if they remain unbroken, they can sometimes form a “ghost” of their former body. They are closely related to sea urchins and starfish, forming a group of irregular sea urchins.

Why do sand dollars have high demand in decorative art?

These marine invertebrates are in high demand for the decorative arts; they’re often used as sand timers and in shadow boxes. They’re also commonly used in jewelry and as collectibles. [Mandal, 2012]

Physical Structure Of Sand Dollars

Sand dollars are spiny, flattened, round, or ovoid-shaped marine organisms found on the seabed. They’re part of the phylum Echinodermata and the class Holothuroidea, which means they share characteristics with other members such as sea stars and sea urchins.

Their skeletons are composed of individual calcite elements called ossicles (a tiny skeletal element fused together), each one shaped like a miniature sand dollar; these ossicles are embedded in the skin, connected by soft tissues. The skeleton can sometimes form a “ghost” of its former body after the sand dollar dies.

The sand dollar’s mouth is located on the underbelly or oral surface; they feed by everting their stomachs through their mouths and using their tube feet to pass food into their mouths. They eat microscopic plants and animals which they strain from the sand they pass through their feeding apparatus.

Sand Dollars
Sand Dollars

How do Sand dollars reproduce?

Sand dollars reproduce sexually by releasing sperm and eggs into the water column or asexually by dividing themselves. They are hermaphrodites; both male and female organs mature at the same time to allow self-fertilization. Sand dollars also reproduce by transverse fission, where they split in half.

The sand dollar’s eggs are fertilized internally and develop into larva; these larvae eventually fall to the ocean floor where they develop into adults.

Sand dollars reproduce asexually by dividing themselves or sexually by releasing sperm and eggs into the water column. They are hermaphroditic and undergo synchronous oogenesis and spermatogenesis at the same time. Sand dollars also reproduce by transverse fission, in which they simply split in half through their middle.  

What is the life span of sand dollars?

Sand dollars can live as long as 25 years, but most die within three to five years. Sand dollars are preyed upon by crabs and other fish. They’re also susceptible to infection; a type of protozoan parasite known as Orchitophrya stellarum attaches itself to the spines on the bodies of sand dollars and slowly kills them.

Sand dollars can also be affected by domoic acid poisoning, which results from exposure to biotoxins produced by a species of algae known as Pseudo-nitzschia.

Sand dollar’s skeletal system

The sand dollar’s skeletal system is a mosaic of small ossicles or plates called “test” which are covered by a skin membrane called the peritoneum. These ossicles are embedded in the skin and connected by soft tissues. The peritoneum plays a role in feeding as it gathers food for ingestion. This “feeding membrane” contains tube feet that provide the sand dollar with locomotion; these appendages are also used in respiration when moving across the ocean floor.

In California’s Catalina Island, a species of barnacle can be found attached atop sand dollars; barnacles are often camouflaged and look like rocks or plants underwater. Sand dollars also attract feather duster worms that grow on and inside them.

What is the feeding method of Sand dollars?

Sand dollars feed by everting their stomachs through their mouths and using their tube feet to pass food into their mouths. They eat microscopic plants and animals which they strain from the sand they move through with their feeding apparatus.

Conclusion

Sand dollars are fascinating creatures, and the sand dollar urchin commonly found on beaches is a great example of this. In fact, the finding of one is often what causes people to visit a beach in the first place.

So what happened? Well, in this particular case, the sand dollar has been bleached by the sun, which leaves it looking a dead and dull white. But don’t be fooled… those ‘dead’ spines are actually very sharp. However, they are much less dangerous than the living urchin with its five venomous spines.

This is why you should always pick up a sand dollar by the flat side and not one of its spines.

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