"The Metamorphosis of Echinoderms," Quart. J. Micr. Sci. xxxviii. 1896, p. 53.
Pelagothuria is said to have no calcifications.
Hjalmar Théel, "On a singular Case of Hermaphroditism in Holothurids," Bih. Svenska Vet. Akad. Hand. xxvii. Af. 4, No. 6, 1901.
Bronn's Thier-Reich, vol. ii. Abt. 3, Buch i. "Die Seewalzen," 1891, pp. 327 et seq.
Genuine suckers appear never to be developed; but the ends of the ventral podia are sometimes rounded, sometimes slightly flattened.