Entocolax, mouth at free extremity, animal fixed by aboral orifice of pseudopallium, Pacific. Entoconcha, body elongated and tubular, animal fixed by the oral extremity, protandric hermaphrodite, parasitic in testes of Holothurians causing their abortion.
Eschscholtz at the Marshall Islands in 1825, Balanoglossus was described as a worm-like animal belonging to the Echinoderm order of Holothurians or sea-cucumbers.
There was also sufficient comprehension of the differences between the main classes of Echinoderms - the sea-urchins or Echinoidea, the starfish or Asteroidea, the brittle-stars and their allies known as Ophiuroidea, the worm-like Holothurians, the feather-stars and sea-lilies called Crinoidea, with their extinct relatives the sac-like Cystidea, the bud-formed Blastoidea, and the flattened Edrioasteroideawhile within the larger of these classes, such as Echinoidea and Crinoidea, fair working classifications had been established.
Among these the abyssal starfish and holothurians described by W.
The theory has been vigorously opposed, notably by Semon (op. cit.), who saw in the holothurians a nearer approach to the ancestral form than was furnished by any calyculate echinoderm, and by the Sarasins, who derived the echinoids from the holothurians through forms with flexible tests (Echinothuridae, which, however, are now known to be specialized in this respect).