from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A larval stage of a mollusk characterized by the presence of a velum.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The planktonic larva of many kinds of marine and freshwater gastropod molluscs, as well as most bivalve molluscs.
from the GNU version of the Collaborative International Dictionary of English
- n. Any larval gastropod or bivalve mollusk in the stage when it is furnished with one or two ciliated membranes for swimming.
from The Century Dictionary and Cyclopedia
- n. One who or that which bears a velum; in Mollusca, specifically, the veligerous stage of the embryo, or the embryo in that stage, when it has a ciliated swimmingmembrane or velum (see velum, 3, and typembryo).
What was discovered in the Wahpeton area is known as a veliger - a microscopic free-swimming zebra mussel that can float for weeks before eventually attaching to something and growing into a dime-size mussel.
They also go through a second larval stage called the veliger stage, which is also a free-swimming stage.
The trochophore matures into a veliger, which is the second stage of its development.
Truncatella breathes with a gill (see my dissection here), but lives its entire life on land near the sea, while Melampus breathes with a lung, lives at the edge of the sea, but enters it to reproduce via planktonic veliger larvae.
Truncatella breathes with a gill see my dissection here, but lives its entire life on land near the sea, while Melampus breathes with a lung, lives at the edge of the sea, but enters it to reproduce via planktonic veliger larvae.
The larvae pass through the veliger stage, while they are still in the marsupium and are only released after they transform into the glochidial stage.
These veliger larvae are free-swimming unlike those of other freshwater bivalves.
Had the littorinids' ancestors evolved a way to modify the veliger larva and at the same time evolved some sort of protective egg, they would have paved the way towards full terrestriality.
Moreover, as Martins1 noted, the species in the subfamily Melampinae, including M. bullaoides, have veliger larvae that start out as plankton in the sea before settling down to more terrestrial lives.
Laurencia pacifica is required to trigger metamorphosis from a free-swimming veliger larva to a small crawling snail, a discovery that allowed him to show the first pictures of the beautiful tiny post-metamorphic juvenile Aplysia.