The Lem Colonist Gauna is the Gauna that took over the Lem Colonist Ship, using it to attack Sidonia. Taking on the approximate shape of the Lem Colonist Ship, it approximated both the crew of the ship and the GCPDS weapons used by Guardians (though without the striking power or damage potential of the GCPDS). Though the Lem Colonist Ship had been successfully defended by Tanikaze Nagate on their outbound voyage, they fell prey to Gauna after they left Sidonia's protection.
The Lem Colonist Gauna is a single Gauna. Unlike the Ocarina, it is not a Small Mass Union Ship; it has a single True Body, though its Placenta is significantly thicker than normal. Inside the Gauna are alternating rings of Placenta and True Body-like material, presenting a significantly more difficult target than previous Gauna. These rings allowed the Lem Colonist Gauna to shrug off shots from the GCPDS, and required multiple shots to pierce through its layers.
After receiving severe damage to its Placenta, the Gauna was able to change shape and composition, and was able to use a large Higgs-particle attack to destroy a Guardian.
The Gauna contained multiple rifle-like projections, letting the Gauna fire long-range shots at the Guardian units engaging it. These rifles appeared to not have as much stopping power as GCPDS; Guardians were able to shrug off some of the shots, and only direct hits were shown to deal critical damage.
The Lem Colonist Gauna was engaged by two Guardian squads and Nagate in the Guardian Type 19 Prototype. Though Samari was the initial pilot for the prototype, her sickness prevented her from piloting it during the fight, and Nagate piloted it instead. At first, the immense power of the prototype seemed to swing the battle in Sidonia's favor, but the rapidly regenerating Placenta and the ranged attack abilities of the Gauna soon proved to be too much for the two squads, even with Nagate's assistance.
With the Guardian teams facing a difficult foe, Shiraui Tsumugi made her debut, piloted by Kunato and destroying 20% of the Gauna's Placenta in a single shot. After discarding her weapon, she ripped through the Lem Colonist Gauna, exposing the last layer protecting the Gauna. After the Gauna changed form, Tsumugi tore a hole through the Gauna, piercing the True Body with her Kabi claws, and foaming the Gauna.