[en] More than 1900 specimens of Pelagosphaera were collected during the «Dana» Expedition. They were caught in all explored seas.
In addition to contracted specimens wich have already been described by previous authors, a few inflated individuals were funds. In front of a spherical body, these larvae present a conical collar with a strong metatroch (fallen in fixed specimens) and a proboscis orientated ventrally.
The anatomical features of the larvae are exactly similar to those described by previous authors. The number of longitudinal muscles as well of retractor muscles is so variable that it is even impossible to try to class the larvae in a definitive species. But it is highly probable that they belong to a Sipunculus.
Some anatomical features are described with more precision, especially the structure of the accessory organs of the mouth and of the nephridia wich are metanephridia.
Some 15 individuals were at the beginning of metamorphosis, but they still retained all the larval organs. The metatroch, in particular, is in perfect state. The colla ris invaded by a lot of muscle fibers and is fringed, so that it seems to be the origin of the tentacles of the adult.
Many Radiolarians and Diatoms were found in the gut of Pelagosphaera.
Pelagosphaera is a trochophore highly adapted to pelagic life. It was caught mostly in the upper 300 metres but above depths of 2000 metres or more.
The study of Pelagosphaera, especially of the specimens in metamorphosis, suggests the the Sipunculids are trochophores adapted to benthic life.
