Covered Tetran is the Tetran variant that appears in Gradius IV. It is the only Tetran that has destroyable arms. In fact, destroying all its arms kills it.
Covered Tetran flails its arms for a few seconds after appearing. During this time, it is invulnerable, even though the core is open. After this, it slowly rotates its arms around the main core, like the normal Tetran. Unlike the normal Tetran, it fires both bullets and mines. These mines can be destroyed, however. Once two arms are destroyed, it will begin to spin them rapidly around its body, making it difficult to approach. It will spin its last arm faster to compensate for the lost ones. Covered Tetran is actually very difficult to destroy properly. Most players destroy the arms, which kills it anyway.