Sand dollar is the general name of a sea animal in the same class as starfish. The sand dollar has a hard, flattened, disc-shaped test or shell made of rigidly bonded plates that lie just below the thin skin. Small thorns that cover the test intensively allow the animal to accumulate in the sand just below the surface. Like other members of the class, the sand dollar is also radially symmetrical. It also shows evidence of a secondary bilateral symmetry, ie the mouth is centered on the mouth surface, but the anus extends near the back edge of the test.

The tube feet are similar to those in other echinoderms, and they use small food particles, which are mostly organic matter in the sand, for conveying to the mouth. They perform their breaths thanks to the tube feet on the upper surface. Sand dollars are separated by shorter spines and a flatter shape than the heart-associated chestnut chest. More convex, short-sleeved sand dollars are also called sea biscuits. Deeper waters of both Atlantic and Pacific coasts are found in sandy sand at the foot of the sand and are classified in the Echinodermata Filum.

Sand Dollar Tag

• Scientific name: Echinarachnius parma

• Common name (s): Common sand dollar or northern sand dollar; Also known as sea cookies, crispy biscuits, sand pies, chestnuts or pansy shells

• Essential animal group: Invertebrate

• Size: Live adult animals diameter between 2-4 inches and about 1/3 inch thick

• Lifetime: 8-10 years

• Diet: Carnivore

• Growing environment : the northern part of the Atlantic and Pacific oceans

The live animals of the species of the common sand dollar (Echinarachnius parma) are usually about 2 to 4 inches in size and are covered with purple, reddish-purple or brown colored spines. Sand dollar test is endoskeleton and is called endoskeleton. Because the sand dollar spines are found under the skin and are made of molten limestone plates. This is different from the skeletons of other echinoderms, starfish, basket stars and fragile stars have smaller plates that are flexible and the sea cucumber skeleton consists of tiny bones embedded in the body.

The top of the sand dollar test (aboral) surface has a structure that looks like five leaves. There are five sets of pipe feet extending from these leaves that the sand dollar uses for breathing. The anus of the sand dollar is found on the back of the animal, on the edge of the test, under a single vertical line extending from the center of the star, and using the spines at the bottom.

Types of Sand Dollar

Sand dollars are echinoderms, which means they are related to starfish, sea cucumbers and sea urchins. In fact, they are basically flat sea urchins and Echinoidea, which is in the same class as the sea urchin. This class is divided into two groups: normal echinoids (sea urchins and pencils) and irregular echinoids (including heart urchins, sea biscuits and sand dollars). Irregular echinoids have a front, back and basic two-sided symmetry above the normal pentameral symmetry (5 parts around a center) of normal echinoids. There are many kinds of dollars in the sand. Outside of E. parma, commonly found in the United States are as follows:

• Dendraster excentricus (Eccentric, western or Pacific sand dollar):They’re in the Pacific Ocean from Alaska to Baja, California. These sand dollars grow around 4 inches and have gray, purple or blackish spines.

• Clypeaster subdepressus (Sand Dollar, sea biscuits): They live in the waters of Brazil, in the Atlantic Ocean and in the Caribbean Sea of ​​Carolinas.

• Mellita subdepressus (keyhole sand dollar or keyhole chestnut): They are found in tropical waters in the Atlantic, Pacific and Caribbean Sea, and there are about 11 types of sand dollars.

The classification of sand dollars is as follows:

• Kingdom: Animalia

• Filum Echinodermata

• Class: Clypeasteroida (includes sand dollar and sea biscuits)

Habitat and Distribution

Common sand dollars were found in the North Pacific and East North Atlantic oceans in areas just below the intertidal region, up to 7,000 meters. As the name implies, sand prefer to live in the sand at densities ranging from 5 to 215 per 10.7 square meters. They use their thorns to find their food and to protect themselves. The adult sand dollars are larger than 2 inches in diameter and live in intertidal regions.

Some sand dollars live in sea water (salty environments), but some species occur in river mouth habitats that combine river and lake water and are chemically different from saline or freshwater environments. Research shows that the sand dollar requires a certain level of salinity to fertilize the eggs.

Nutrition and Behavior

Sand dollars are fed with small food particles in the sand, typically fed by algae in microscopic size, but are also classified as carnivores according to the records of other marine species. The particles descend on the spines, then are transported through the tube feet and the mucous cilia to the mouth of the sand foot. Some sea urchins stand on the edge of sandy areas to maximize their ability to capture floating prey. Like other sea urchins, the mouth of the sand dollar is called Aristotle’s lighthouse and consists of five jaws. When a sand dollar test is taken and shaken slightly, parts of the swinging mouth can be heard.

Reproduction and offspring

Male and female sand dollars, it is difficult to say which is the outside. Reproduction is sexual, provided with sand dollars that leave eggs and sperm in the water. Fertilized eggs are yellow in color and covered with a protective gel. The average diameter can vary from about 135 microns or about one inch to about 1/500. They grow into small larvae that feed and move using lashes. After a few weeks, the larvae settle to the base of the metamorphosis.

The offspring (below 2 inches) are found in subtidal regions and, as they mature, gradually pass into exposed beach areas, the smallest being found in the highest beach elevations. They bury themselves in the sand to a depth of two inches, and very dense populations can push themselves into the depths of three animals.

Threats

The ability of the dollar to be tested may be affected by fishing, in particular by the bottom trawl and by ocean acidification. Climate change and reduced salinity, which may affect existing habitat, reduce fertilization rates. Sand dollars are not consumed by humans, but they can hunt for starfish, fish and crabs. Sand Dollars are not currently listed as an endangered species.

Sand Dollar and People

Sand dollar tests are sold in a shell or card, on the internet, for decorative purposes or for souvenirs and usually with a card or letter referring to the Legend of the Sand Dollar. Such references are related to Christian mythology. They argue that the five-pointed star in the center of the summit of the sand dollar is a representation of the Bethlehem Star, which directs the wise men to the baby Jesus. The five openings in the test are said to represent the wounds of Jesus during his crucifixion, with four wounds on his hands and feet and the fifth near him. Under the sand dollar test, Christmas is said to be a draft of a poinsettia, and when it is opened, it is indicated that there will be five small bones representing the peace pigeon. These pigeons are actually five jaws of the sand dollar mouth.

References:

jstor.org

marinespecies.org

eol.org

journals.uchicago.edu