Dendrasteridae Family of Sand Dollars
One Sand Dollar from the Dendrasteridae Family can be found in this website:
Eccentric Sand Dollar, Dendraster excentricus. A representative of the Dendrasteridae Family of Sand Dollars.
Phylogeny: Dendrasterid Sand Dollars are members of the Dendrasteridae Family and along with sea stars, basket stars, sea cucumbers and sea urchins are in the phylum Echinodermata. These Sand Dollars, along with heart urchins and sea biscuits, are irregular Urchins in the class Echinoidea. They differ from regular urchins in that they are not radially symmetrical, but instead have bilaterally symmetrical. They are in the order Echinolampadacea, the suborder Scutelloida, the infraorder Scutelliformes, and the superfamily Scutelloidea. The Dendrasteridae Family is one of four families in this superfamily. The Dendrasteridae Family is small, with only one genus and three species. Species in the family are also commonly called Dendrasterids. The name Dendrasteridae comes from the Greek words meaning “tree” and “star”. This refers to the branching tree-like pattern of grooves on the oral surface and the petaloid star shape on the aboral surface.
Morphology: Dendrasterid Sand Dollars have a very flattened profile and an irregular circular profile, with a flat margin posteriorly. The aboral (dorsal) surface is slightly humped and oral (ventral) surface is flat. They have a rigid test (external skeleton) that is perforated with multiple pores and contains all of the organs, except for the epidermis. They have a 5-petalled pattern on the aboral surface. This petaloid design on top is made of pairs of pores which allow for respiration through specialized tube feet. Their mouth and a modified Aristotle’s Lantern (complex jaw structure) is located centrally on the oral surface. Grooves, lined with cilia, direct food to the mouth. The epidermis is covered with small spines, which facilitate movement over, and through, soft substrates. Young sand dollars ingest sand and store it in their gut, to serve as ballast. Living Sand Dollars are brown, gray or purple in color. The tests of dead specimens quickly bleach to white. They can reach a maximum of 10 cm (3.9 inches) in diameter and 1.0 cm (0.4 inches) in height. Dendrasteridae Sand Dollars differ from the Mellitidae Family of Keyhole Sand Dollars by lacking the five or six lunulae through their test.
Distribution: Dendrasterid Sand Dollars are found on sand or muddy sand substrates. They live in the lower intertidal zone, and to depths of around 90 m (295 feet). Dendrasterid Sand Dollars are found in the temperate to subtropical Eastern Pacific. Three species fromthe Dendrasteridae Family are found along the Pacific coast of Mexico.
Reproduction: Dendrasterid Sand Dollars are generally gonochoric (male or female for life). They reproduce by broadcast spawning, with external fertilization. Eggs are brooded by the parents and the planktonic larvae metamorphose through several stages over a long period of time before the test is formed, at which point they become benthic. These Sand Dollars also have the ability to reproduce asexually via larval cloning, a mechanism of self-defense that doubles their numbers while effectively halving their size making them less attractive for predation.
Ecosystem Roles: These Sand Dollars are depositional feeders that consume algae, larval crustaceans, diatoms, detritus and mollusks. In turn they are preyed upon by fish, mollusks and starfish.