Sand Dollars

Sand Dollar Clypeasteroida

Sand Dollar Clypeasteroida

Sand Dollar Clypeasteroida

Sand Dollar Clypeasteroida

Sand Dollar Clypeasteroida

Sand Dollar Clypeasteroida underside

The aboral side of the shell (test) has the off-centered petalidium, as seen clearly here in a dead specimen which has lost its spines. Note also that, unlike urchins which have 5, sand dollars have only 4 gonopores, visible around the star-shaped pattern in the center.

The oral (under) side of the test is flat. It has the mouth in the middle, with tracks leading to it. The anus is near the edge of the shell (at the bottom in this photo).

Although no external ridges are visible around the mouth from the outside (see previous photo), this broken piece shows that 5 radiating ridges around reinforce the test on the inside. Photo by Dave Cowles, July 2010.

Live Dendraster excentricus on sand in an aquarium at Shannon Point Marine Center. Found subtidally in Bellingham Bay. Diameter 6 cm. (Photo by: Dave Cowles, August 2006)

Green sea urchins; Levende zeeboontjes.

Eccentric Sand Dollar (Dendraster excentricus), Ganges Harbour, Salt Spring Island, British ColumbiaSource: http://en.wikipedia.org/wiki/File:Eccentric_sand_dollar.jpg

Encope cocosi, holotype, aboral spinesEncope cocosi, holotype NHMLA 39.1, Bahia Wafer, Isla de Cocos, Costa Rica

Encope cocosi, holotype, posterior lunuleEncope cocosi, holotype NHMLA 39.1, Bahia Wafer, Isla de Cocos, Costa Rica

Encope cocosi, holotype, lateral view (anterior to right)Encope cocosi, holotype NHMLA 39.1, Bahia Wafer, Isla de Cocos, Costa Rica

Encope cocosi, holotype, oral view Encope cocosi, holotype NHMLA 39.1, Bahia Wafer, Isla de Cocos, Costa Rica

Encope cocosi, holotype, aboral view Encope cocosi, holotype NHMLA 39.1, Bahia Wafer, Isla de Cocos, Costa Rica

Encope californica, lateral view of denuded test (anterior to right)Encope californica, Mogote, La Paz, Mexico, Gulf of California.

Encope californica, oral view of denuded testEncope californica, Mogote, La Paz, Mexico, Gulf of California.

Encope californica, aboral view of denuded testEncope californica, Mogote, La Paz, Mexico, Gulf of California.

Encope fragilis, holotype, posterior lunuleEncope fragilis, holotype NHMLA 43.4, North of White Friars, Guerrero, Mexico

Encope fragilis, holotype, aboral spinesEncope fragilis, holotype NHMLA 43.4, North of White Friars, Guerrero, Mexico

Encope fragilis, holotype, lateral view (anterior to right)Encope fragilis, holotype NHMLA 43.4, North of White Friars, Guerrero, Mexico

Encope fragilis, holotype, oral viewEncope fragilis, holotype NHMLA 43.4, North of White Friars, Guerrero, Mexico