Complex sentence: The smallest are a few millimeters long, most are less than, several exceed, and the longest animal ever found, at long, may a specimen of "Lineus longissimus", although "L. longissimus" is usually only a few millimeters wide.
Split into simpler sentences: The smallest are a few millimeters long, most are less than, and several exceed. The longest animal ever found, at long, may a specimen of "Lineus longissimus", although "L. longissimus" is usually only a few millimeters wide.