Morphology
These snails float and swim freely in the water, and are carried along with the currents. This has led to a number of adaptations in their bodies. The shell and the gill have disappeared in several families. Their foot has taken the form of two wing-like lobes, or parapodia, which propel this little animal through the sea by slow flapping movements. They are rather difficult to observe, since the shell (when present) is mostly colorless, very fragile and usually less than 1 cm in length. Although their shell may be so fine as to be transparent, it is nevertheless calcareous; their shells are bilaterally symmetric and can vary widely in shape: coiled, needle-like, triangular, globulous.
The shell is present in all stages of the Cavolinioidea (euthecosomata) life cycle, whereas in the Cymbulioidea (pseudothecosomata), adult Peraclididae bear shells, Cymbuliidae shed their larval shells and develop a cartilaginous pseudoconch in adulthood, and Desmopteridaen adults lack any rigid structure.
Read more about this topic: Sea Butterfly
Famous quotes containing the word morphology:
“I ascribe a basic importance to the phenomenon of language.... To speak means to be in a position to use a certain syntax, to grasp the morphology of this or that language, but it means above all to assume a culture, to support the weight of a civilization.”
—Frantz Fanon (1925–1961)