Giant squid
From Wookieepedia, the Star Wars wiki.
The Giant squid were creatures that lived in the oceans of Mon Calamari.
While traversing the oceans of Mon Calamari, Luke Skywalker's minisub was caught by a giant squid. These creatures were very rare and highly dangerous, grabbing and pulling down to the depths any creature, (or vehicle) that comes near its territory.
This species is likely related to the Devilsquid also native to the planet.
