Level 7 Crimson Fists Sergeant has Tarantula Mk2 in one of his two equipment slots. When reching level 8, the game places Tarantula Mk1 in the third slot. As long as you do not touch either of those two slots, you keep both.

On a related note, Crimson Fists paint Tarantulas in yellow. Just like Imperial Fists do.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=862309996

And another Tarantula bug:
The Mk2 version has no audio for shooting, i.e. no bullet sound. At least the yellow Crimson Fists' version.