TT #35 · Parashas Noach · Third Aliyah · Passuk 8:19
Every animal, every creeping thing, and every bird, everything that stirs on earth came out of the ark by their families.
Torah Temimah points to Sanhedrin 108b (by families — not they themselves for boneless creatures).
E-Daf image — Sanhedrin 108b (size=3)
English: “By their families they went out” — by their families, and not they themselves (i.e., creatures without bones that cannot live twelve months left only through their offspring).
Custom (diyuk excluding boneless creatures from the original entrants).
Boneless creatures (which cannot live twelve months) did not themselves exit; only their families/offspring did.