Pnei Moshe Shabbos 1:3

The Pnei Moshe on Maseches Shabbos, Perek 1, Halacha 3 explains:

“And not from the chilazon have we heard.” Meaning, this supports what Chizkiyah said: “One who kills a louse on Shabbos is like one who kills a camel.” Even though a louse is not considered a significant creature since it has neither sinews nor bones, nevertheless, have we not heard this about the chilazon? For we learned in the Tosefta (Perek 9): “One who traps a chilazon and crushes it is liable for two chata’os.” But the chilazon—does it have sinews and bones?! It is a type of Tolaas! Yet still, one who kills it on Shabbos is liable. The same applies to a louse.