The Eccentric Sand Dollar is, at least among its fellow echinoids, precisely that: eccentric. Their behavior is very different from other related species.
In regions of steadily flowing water, this creature gathers in large groups and then they align themselves in rows, on the ocean floor. They then dig their front edge into the sand and leave the back portion raised up. This cooperative effort, along with the shape of their bodies, generates a natural hydrofoil effect.
The action draws food closer to their mouths, in a communal feeding. In some areas, tens of thousands of the Eccentric Sand Dollar may be present forming such communal feeding groups, all aligned in neat rows.
Eccentric Sand Dollar Physical Characteristics
The Eccentric Sand Dollar is highly variable in size. They attain a maximum known carapace diameter of roughly 4 in (10 cm), though most are considerably smaller. Their coloring varies, but typically includes shades of brown, gray, black, or even purple.
Their body is roughly disk-shaped, with a small dome in the center of their chitinous covering. The body itself is tiny, including numerous small, tube feet.
The mouth is on the underside of the carapace, in the approximate center.
Sexual dimorphism is not present in this species. The Eccentric Sand Dollar reproduces through a method known as broadcast spawning.
Eccentric Sand Dollar Range, Habitat, and Ecology
The Eccentric Sand Dollar is endemic to the shallow coastal waters along the west coast of North America, from Alaska to Baja, California.
They most typically inhabit subtidal zones, such as bays, rarely living at depths of more than 164 ft (50 m).
They themselves possess very few natural predators due to the simple fact that they are almost all skeleton.
The greatest threats to their existence are, in fact not surprisingly, human-related. These include tourist trade and destructive fishing practices, such as bottom trawling.