Arachnus are armadillo-like creatures found on SR388. They appear on SR388 in Metroid II: Return of Samus and appear in a mimicked form in Metroid Fusion. Arachnus appear much less often than most other creatures on SR388. An X Parasite mimics an Arachnus aboard the B.S.L research station. They are capable of attacking by with fireballs and they can also ram their targets.
Metroid II: Return of Samus
In Metroid II, Samus battles an Arachnus on SR388 that was previously mimicking an Item Sphere on a Chozo Statue. After Samus shoots the Sphere, it starts bouncing around and attempts to hit her. On occasion, it will stop to shoot a fireball. Samus can only damage it by dropping Morph Ball Bombs directly into its path, as any other attacks it will simply dodge. Once she defeats it, Samus acquires the Spring Ball.
In Fusion, Samus battles an X mimic of an Arachnus on the Main Deck of the B.S.L Research Station. This Arachnus, due to the nature of the X, is much more aggressive than the one seen on SR388's surface. Its basic fighting abilities are similar to the one Samus fought on SR388, but the X mimic has a variety of other abilities. From its claws, it can unleash a large wave of energy, and its fireballs detonate on the ground, creating a wave of flame in its wake. Samus can defeat it by firing at its exposed chest, but its shelled back is invulnerable.
Metroid: Samus Returns
Arachnus returns in Metroid II's remake, Samus Returns. Like Fusion, he is vulnerable to missiles hitting his front.
- Arachnus-X was seen in the first trailer for Metroid Fusion, and was amongst the first enemies to be revealed from the game pre-release.
- There is a beta image of Arachnus from Fusion showing it scream into the air, a function that was removed before the game's release. The image also shows other unused features, such as the color palette for the scene and Samus's health bar.
- A remix of Arachnus-X's theme is used in Metroid Prime 3: Corruption during the boss battle with the Berserker Lord. Both bosses are the first in their respective games.
- The Arachnus boss in both games rewards Samus with a Morph Ball-related upgrade: the Spring Ball in Metroid II, and the Morph Ball in Fusion.
- In the later Japanese version of Fusion (and likely II as well), this creature is known as the "Marukara" (マルカラ), which carried over to the Metroid Prime & Fusion Original Soundtracks.