Water Slug

Water slug (tentatively Seaslug hydroclast). A biological enigma that converts seawater into drinkable fresh water.

1. Microbial fuel cell
Removing salt from seawater is energy-intensive. Nonetheless, the water slug does it, perhaps as a byproduct of an internal microbial reactor that feeds on waste in seawater.

2. Fresh water reserve
A hydrophobic plastic bulb that protects the slug from rapid dehydration by saltwater.

3. Plankton farm
The slug's water bulb hosts a highly productive plankton species, turning light into food. Fresh water may be necessary for the plankton's chemistry, or it may be a prison—a way to keep the plankton from leaving.

4. Vampiric aura
The water slug's developed beak has a sharp cutting surface. Possible evolutionary history as a parasite or commensal, tapping a host's blood and filtering out toxins.

Assessment: only nearby source of drinkable water. Advise fabricator cook before drinking. In case of kidney problems, consider allowing the water slug to feed on your blood.