Echinoderm Larvæ and their Bearing on Classification

Abstract

DR. MORTENSEN (NATURE, December 16, p. 806) says that “since the larvæ of the more primitive Asteroids (the Phanerozonia) are devoid of a Brachiolaria stage, the sucking discmust be a later specialised structure” Surely the statement is an error, and (even if it were true) the conclusion unjustified. The Phanerozonia of Sladen includes eight families. One of these families, the Asteropectinidæ, contains species with non-attaching larvæ. Two other families (the Asterinidæ and the Gymnasteriidæ) have species with attaching larvæ (Asterina, Q.J.M.S., 1896, and Porania, Q.J.M.S., 1915). It is true that the Asterinidæ approach the Cryptozonia in some respects, but taken by itself this fact might rather lead us to look on the Asterinidæ as “primitive”—an annectant family between the two great orders of starfish. The Gymnasteriidæ are frankly Phanerozonate.