They are also popularly known as sea-eggs.

Utterly devoid of limbs, the locomotion of these creatures is effected by means of rows of small tubular suckers (which protrude through pores in the calcareous plates) and by moveable spines scattered over the body.
[Illustration: PEDICELLARIAE.

(Immensely enlarged.)] Besides these spines and suckers there are certain very peculiar structures, termed "Pedicellariae." Each of these consists of a long slender stalk, ending in three short limbs--or rather jaws--the whole supported by a delicate internal skeleton.

The three limbs (or jaws), which start from a common point at the end of the stalk, are in the constant habit of opening and closing together again with a snapping action, while the stalk itself sways about.

The utility of these appendages is, even now, problematical.
It may be that they remove from the surface of the animal's body foreign substances which would be prejudicial to it, and which it cannot otherwise get rid of.