It is found in the North Pacific and Northwest Atlantic, on the North American east coast from New Jersey north, as well as in Alaska, Siberia, British Columbia, and Japan. It inhabits isolated areas on sandy bottoms below the low tide level down to a depth of 5,000 feet (1,500m).
Description
The tests (shells) of these sand dollars are round, flat and disc-like, typically measuring 3 inches (7.6cm) in diameter. The growth rate for this animal is between 3.5 and 6mm/yr in the latter 5 years of their lifespan, and the lifespan is typically around 8 years.[2] The entire shell is also covered with maroon-colored moveable spines. The color is a purplish brown, becoming bleached white when deceased and washed ashore. This color occurs due to only the hard, calcified exoskeleton remaining, with further bleaching by sun and saltwater as it reaches the shore. As in other echinoderms, they have five-fold radial symmetry, with a petal-shaped structure, or petalidium, on the aboral surface. The feet containing small hair-like structures (cilia) are located on this surface.The mouth, food grooves, and anus are located on the bottom side of the animal.
This and other species of Echinarachnius have been around since the Pliocene epoch.
Feeding
In terms of feeding, sand dollars are suspension feeders that rely on a specialized structure called Aristotle's Lantern. Their cilia create grooves on the underside of their body that funnel food particles like plankton, detritus, and microscopic organisms toward their central mouth. Their interlocking teeth, known as "doves," work together to grind and process food. This feeding strategy allows them to extract nutrients from the surrounding sediment and water. They are opportunistic feeders.
Reproduction
The reproductive strategy of the common sand dollar includes both sexual and asexual methods, with the latter being particularly fascinating. Sand dollars typically reproduce sexually through external fertilization, where eggs and sperm are released into the water column. However, under certain conditions, particularly in the larval stage, sand dollars exhibit a form of asexual reproduction.
When faced with predation threats, sand dollar larvae can reproduce asexually through budding or fission. This response allows the larvae to split into smaller clones, which are less detectable by predators. The process not only increases the larvae's chances of survival but also enhances the population's ability to persist in predator-rich environments. This strategy is thought to be an evolutionary adaptation to reduce predation pressure on vulnerable larvae.[3][4]
Say, T. (1826). On the species of the Linnean genus Echinus, inhabiting the coast of the United States. Journal of the Academy of Natural Sciences of Philadelphia. 5, 225–229
Gosner, K. L. (1971). Guide to identification of marine and estuarine invertebrates: Cape Hatteras to the Bay of Fundy. John Wiley & Sons, Inc. 693 p.
Linkletter, L. E. (1977). A checklist of marine fauna and flora of the Bay of Fundy. Huntsman Marine Laboratory, St. Andrews, N.B. 68: p
Mortensen, T. (1948). A Monograph of the Echinoidea. IV, 2. Clypeasteroida. Clypeasteridæ, Arachnoidæ, Fibulariidæ, Laganidæ and Scutellidæ. 471 pp., C. A. Reitzel, Copenhagen.
Bromley, J.E.C., and J.S. Bleakney. (1984). Keys to the fauna and flora of Minas Basin. National Research Council of Canada Report 24119. 366 p
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