In Echinoneus, the shell is described by M.Perrier as bearing two kinds of pedicellariae, one resembling those of Echinus, and the other those of Spatangus; and such cases are always interesting as affording the means of apparently sudden transitions, through the abortion of one of the two states of an organ.
With respect to the steps by which these curious organs have been evolved, Mr.Agassiz infers from his own researches and those of Mr.
Muller, that both in star-fishes and sea-urchins the pedicellariae must undoubtedly be looked at as modified spines.

This may be inferred from their manner of development in the individual, as well as from a long and perfect series of gradations in different species and genera, from simple granules to ordinary spines, to perfect tridactyle pedicellariae.
The gradation extends even to the manner in which ordinary spines and the pedicellariae, with their supporting calcareous rods, are articulated to the shell.

In certain genera of star-fishes, "the very combinations needed to show that the pedicellariae are only modified branching spines" may be found.

Thus we have fixed spines, with three equi-distant, serrated, movable branches, articulated to near their bases; and higher up, on the same spine, three other movable branches.
Now when the latter arise from the summit of a spine they form, in fact, a rude tridactyle pedicellariae, and such may be seen on the same spine together with the three lower branches.

In this case the identity in nature between the arms of the pedicellariae and the movable branches of a spine, is unmistakable.