Calcinite
A terror unit that may accompany the Aquatoids on land missions. Fortunately, while its diving suit makes a good disguise, no Terror mission involves civilian aquanauts. So unless you have an agent obsessed with yellow diving suits (and refuses to take off his helmet on land), there should be no problem identifying this armored blob. The creature's corpse also provide information needed to study melee weapons like the Vibroblade. Unfortunately for the scientists, Aquatoids don't enjoy terror missions much and X-Com commanders may never encounter this green blob.
Live Specimen
In the diving suits of lost mariners, these aliens stalk the seabed for the unwary. A vicious swipe by the creature's stronger than steel claws can be enough to send the best divers to the bottom.
A gelatinous green form can be seen swirling around in the face mask. No hint of the real creature can be divined from the often lethal encounters we have had with them.
Autopsy
Once the armoured suit is stripped away the Calcinite is revealed to be a huge amorphous blob of protoplasm. No visible brain, limbs or sensory organs exist, a small metallic component resides deep in the liquid body.
Once dead we can only guess at the creature's nature. An inexplicable enigma of our alien enemies.