Grenchler

Grenchlers are amphibious predators that live in Torvus Bog, Aether. They will attack anything that moves with their jaws and fire energy bursts when it can't reach its prey.

The shell on the Granchler's back is susceptible to explosives and once its shell is removed, the Grenchler is vulnerable to attack from behind. However, it is usually a better strategy to use Charge Beam shots - even the charged Power Beam does more damage than missiles, and although missiles achieve a better fire rate, this usually does not mean much as the shell is usually vulnerable for short periods of time, so when fighting them it is best to keep the equipped beam charged, and attack when they become vulnerable. Interestingly Grenchlers fade away more slowly than other enemies so they can be scanned even when dead. In Dark Torvus Bog, Samus battles Dark Grenchlers, which are Ing-possessed Grenchlers.

The Grenchlers fought during the game are most likely adolescents or even infants, as much larger carcasses can be seen in Temple Grounds and Torvus Bog. 242 shots from Federation weaponry were required to bring one down, while another was electrocuted on exposed wires, foreshadowing the Grapple Guardian encounter, which is also an adult Grenchler, albeit possessed by an Ing who stole Samus's Grapple Beam.

Creature similarities
Grenchlers are similar to the Baby Sheegoths, from Metroid Prime. This is mainly based on the two creatures' similar behavior and attack patterns, as well as the existence of a larger variant and "boss" form of the species (Sheegoth and the Grapple Guardian, along with the previously mentioned large, dead Grenchlers). However, this is likely in regards to the developers wanting an enemy in Metroid Prime 2: Echoes similar to Baby Sheegoths, but in a different environment. The key differences besides appearance is the Grenchler's ability to jump and swim underwater, both skills that Sheegoths do not have. Also, Sheegoths attack by breathing ice, while Grenchlers attack with bolts of electricity and are seemingly more agile than the former Sheegoths. Grenchlers deal more damage as well; at close range they will use a powerful impaling attack, and at long range they will rely on firing strong, guided bolts of electricity which are much harder to evade than the ice blast of a Baby Sheegoth. However, the Baby Sheegoth is capable of freezing its target.

As it is mentioned off-handedly in Prime 2 that the Luminoth and Chozo had interacted in the past, it leads to a possibility that the two space-faring species may have exchanged local flora and fauna. These introduced lifeforms could have been genetically modified or simply allowed to evolve into their new home habitat. This conclusion explains the similarities of many dual-planet species, such as War Wasps, Triclops/Mechlops and Grenchlers/Sheegoths. It also explains the similarities between organisms seen on Tallon IV and life-form styled mechanoids seen on Aether.

Trivia

 * Without their armor, Grenchlers also look quite similar to the shriekers in Tremors 2: Aftershocks.
 * The Grenchlers, along with the Grapple Guardian, have body structures very similar to the ones belonging to Motos, Gigafraugs, as well as both infant and mature Sheegoths. These creatures' designs may have inspired the creation of one another.
 * Grenchler's appear to have eight eyes visible on each side of their head, with an additional eye behind the lower jaw.