Momoo named on-page (Ch. 73 page 6). Heavy-quadruped sea-cow with horns and nose-ring. Summoned by Hatchan’s trumpet from an underwater kelp/anemone cave. The chapter’s Heavy Combat Beast role-card formalizes Momoo’s slot in the Arlong-Pirates organizational chart — combat-asset, not crewmate.
The payoff
Momoo recurs as a too-traumatized-to-fight-Luffy register in subsequent cameos. The chapter’s Heavy Combat Beast role is set up for peaceful-after-Luffy-trauma later:
Coby/Helmeppo cover-story (later) — Momoo encountered again, flees from Luffy on sight.
Davy Back Fight cameo — Momoo as a thrown-projectile by Foxy.
Why this matters
Oda installs Momoo as a recurring slapstick-monster whose first appearance is in Grand-Line-tier register and whose later appearances are in Luffy-trauma-comic register. The Ch. 73 introduction is the only serious-combat appearance of Momoo in the series; every subsequent appearance reads as a callback to this defeat.
Payoff — Ch. 82 (Heavy-Combat-Beast role-card paid off via redeployment + flinch-and-flee pivot)