Debate Responses
Item
R’ Perr argues that calling the chilazon a “fish” excludes a snail and that if Chazal meant a snail they would have said shavlul. But dag in Chazal is a broad term — the Torah calls sea-serpents dag gadol (Bereishis 1:21), and Rambam (Hil. Berachos 8:10) uses dagim to cover all sea creatures. “Caught like fish” (Menachos 44a) describes its harvest method, not its taxonomy, so calling the chilazon a “fish” does not exclude a shelled creature.
The Arukh defines nartik as an enclosure:
ערוך ערך נרתק:
“משניטל הארון בשעת הכנסת כלים לנרתק שלהן … לכשתצא חמה מנרתקה פי’ מנושתקה … ולפעמים שם כללי לכל תיק.”
“When the Ark was removed they would place the vessels in their nartik … when the sun emerges from its nartik — meaning from its cover … and sometimes it is a general term for any case or container.”
And Rashi writes:
רש״י מגילה כו ב:
“תיק ונרתיק – חדא היא, אלא שלשון ‘תיק’ נופל על דבר ארוך ולשון ‘נרתיק’ נופל על דבר קצר.”
“Tik and nartik are the same thing — a case. ‘Tik’ refers to something long, ‘nartik’ to something short.”
Together, these show that nartik means a case or enclosure. A mollusk shell is literally such an enclosure — the animal “makes it for itself,” exactly as Chazal describe. Shavlul in Shabbos 77b refers to a slimy land snail that leaves trails, not a rare sea creature with halachic significance. Chazal often use distinct terms for sea species (compare tzav for a land turtle vs. tannin for a sea reptile).
Even the simanim in Menachos 44a aren’t meant as strict biological markers. “Once in seventy years” is interpreted in multiple ways:
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Natural cycle: Many shellfish swarm to the coastline in rare intervals, sometimes triggered by storms.
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Once-in-a-lifetime: R’ Benzion Halberstam explains that “seventy years” was the biblical shorthand for a human lifetime — so the phrase means “rare in a lifetime.” He notes a Roman event where a healthy Roman rode on the shoulders of a crippled Jew (symbolizing Esav over Yaakov) — and says the chilazon surfaced in greater numbers at that time to provide tekhelet more widely.
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Never / extremely rare: Dr. Ziderman has verbally noted that “seventy years” can be a rabbinic idiom for something that virtually never happens — like the Gemara’s statement that a Sanhedrin executing once in seventy years is a murderous court.
These interpretations show that the phrase is not literal biology but a way to describe rarity. Combined with “its body resembles the sea” (camouflaged or sea-colored) and “its blood is used for tekhelet,” the simanim point us toward a rare sea creature whose very casing (nartik) must be opened to extract its dye. The murex remains the best fit we have.