Raavya, Hilchos Shabbos, siman 194, §20

The Raavya calls the Chilazon a תולעת (tola’as) and states that it has no עור (or), in the context of liability for chaburah on Shabbos. Neither description identifies the creature as a literal “worm” in the modern zoological sense.

The term תולעת is considerably broader. Rashi (Chullin 85b), for example, describes the יאניבא that damages flax as תולעת האוכלת פשתן and identifies it in Old French as טיינ״א (teigne), a moth/clothes-moth. (Wikisource) Thus tola’as can encompass creatures very different from what modern English speakers ordinarily picture when hearing the word “worm.”

Nor does אין לו עור mean that the Chilazon lacked a shell. The Raavya is discussing עור, skin or hide, for purposes of chaburah. A soft-bodied mollusk enclosed in a hard shell presents no difficulty.

This is particularly noteworthy because elsewhere the same Raavya uses פורפירין / פורפירא (purfirin / purpira) in explaining Techeiles. The manuscript reading of his passage gives the natural parallel Techeiles — purfirin; karti — prasinin, with prasinos meaning leek-green.

Accordingly, the Raavya’s חלזון תולעת ואין לו עור provides no zoological objection to a shelled marine gastropod such as the Murex. Translating תולעת simply as “worm” without qualification gives the word a specificity that its usage in the Rishonim does not warrant.