Infected Slugs: Case #4

In a similar manner to Case #1, this slug keeled over right in front of me and then was eaten by a fellow slug. Like Case #1, the body of Case #4 was lumpy, but unlike that first case, this one had no visible growths. My attention was first drawn to this slug because of its abnormal body shape and mantle. However, since the slug had no external growths on its body, I can't determine if it was infected by parasites or was suffering from some other ailment.

Case #4 was crawling among the lily leaves and began munching on a sunflower shell, when suddenly it reared back, retracting its tentacles, and fell over. It didn't die in that instant, but it obviously experienced some adverse sensation.

It lay there for some time and, rolling it over to get some different angles, I could see colors and forms below the skin in its neck area: whether these were simply displaced organs or parasitic masses, I can't say, but in a healthy slug the mantle and skin pigment usually provide cover for this area.

Colored forms...That yellowish mass could be a parasitic growth, but it could also be an organ.

A white mass partially covering the retracted right tentacle inside...could be genitalia. 

Now, at one point the slug extended its left cephalic tentacle, then the right (or perhaps they extended of their own accord, there being still nerve function in the muscles), but these quickly drooped. 

In lieu of growths, the appearance of the mantle can provide a clue to a slug's physical condition, and this one seemed to be strangely shrunken and ill-fitting. 

The slug did retract its tentacles again, before extending them once more when the healthy slug began to feed on its body. Again, I believe that slugs are able to sense when their fellows are sick or dead, and feed on them accordingly.

Now its tentacles have drooped for good, as though their extension was the slug's last gasp.

When the healthy slug had eaten enough, it crawled away.

You can see that the slug's radula didn't do that much damage, but it did penetrate and expose some tissues. I don't know what that black substance is.