Planet of the Damned

This is page turning story that keeps you wondering how it will end. It explores the notion of symbiosis and it's advantages and disadvantages. The characters are typical of a pulp novel: strong independent man, weak and emotional woman, cruel and evil antagonists.

Doesn't belong on your short list, but a pleasant read overall.

The original title 'Sense of Obligation' is referenced in the story, unlike the later pulp title, which is just used to catch the buyer's eye.