Green Lobiger

This slug steals a chemical weapon rather than a solar panel.

Caulerpa, the grape weed it lives on, defends itself with caulerpenyne, a compound that turns sticky and toxic within seconds of the alga being damaged. Lobiger and its relative Oxynoe eat it anyway, and convert the caulerpenyne into oxytoxins that end up in their own mucus. The slug is drinking a defended plant and reissuing the defense under its own name.

It is choosy about which plant. Caulerpa species differ widely in how much of the compound they carry, and this slug works the middle of the range, on weeds like the grape Caulerpa racemosa rather than the mildest or the strongest. On a standing bunch of it a bright green 3 cm slug is close to invisible.

The four finger-like lobes on its back are the second line. They are usually carried rolled up, and a disturbed animal flicks them open, which roughly doubles its apparent size and shows color patches that were not there a moment before. Push it further and the lobes come off altogether, exuding a sticky secretion and writhing on the spot while the slug crawls away. They grow back.

Between the lobes sits a small transparent shell, too small to withdraw into and no use as armor, left over from ancestors that had a proper one. What this animal does not have is the family's famous trick: when photosynthesis was measured across the sacoglossans, Lobiger viridis registered zero. It drains Caulerpa cells and digests what it takes, chloroplasts included.

Search calm shallow bays with standing Caulerpa, mostly after dark, and expect to find nothing on most attempts.