Clypeasteridae Family of Sea Biscuits

One Sea Biscuit of the Clypeasteridae Family can be found in this website:

Europacific Sea Biscuit, Clypeaster europacificus. A representative Sea Biscuit of the Clypeastgeridae Family.

Phylogeny: Sea Biscuits of the Clypeasteridae Family are members of the phylum Echinodermata and the class Echinoidea. As such, they have have either globose or disk-like bodies that are enclosed in a rigid endoskeletal shell called a test. They have radial symmetry and moveable external spines. They are in the order Clypeasteroida of irregular sea urchins,  also commonly known as sand dollars. This order contains only one suborder-Clypeasterina. The Clypeasteridae Family is the only family in suborder Clypeasterina. The Clypeasteridae Family consists of three subfamilies, four genera, and around forty-eight species. The name Clypeasteridae is derived from both the Greek and Latin words meaning “round shield star”.

Morphology: Sea biscuits are disk-like, with a flattened to inflated profile. The dorsal side of the test may be slightly or strongly humped and the ventral or oral surface is flat or concave.  In outline, adults may have an ovate, rounded pentagonal, or star shape. Juveniles have a more circular outline. The 5-petalled pattern on the dorsal surface is variable. It may be open or closed, with rounded or lyre-shaped petals. The petals may be short or extend to the margin. The pores that delineate the petals come in pairs, and can be round or elongate. These pores allow for respiration through specialized tube feet. Like other urchins, they have a mouth (located centrally on the ventral surface) and a modified Aristotle’s Lantern (complex jaw structure). Grooves, lined with cilia, direct food to the mouth. The epidermis is covered with small spines, which facilitate movement over, and through, soft substrates. Some species in this family have a double-walled test. Sea Biscuits are medium to large in size, with the largest species reaching a maxium of 30 cm (11.8 inches) in diameter.

Habitat and Distribution: Sea Biscuits are generally found on sandy substrates. They live in the lower intertidal zone and to depths around 216 m (709 feet). They are found worldwide in temperate to tropical seas. Six species from the Clypeasteridae Family are found in Mexican waters.

Reproduction:  Sea Biscuits are gonochoric (male or female for life). They reproduce sexually through broadcast spawning, with external fertilization. The fertilized eggs hatch into planktonic larva. These larva eventually settle to the sea floor and develop into their adult form.

Ecosystem Roles:  Sea Biscuits are depositional feeders that consume algae, larval crustaceans, diatoms, detritus, and mollusks. In turn they are preyed upon by fish, mollusks and starfish.