Hope 2007 rox yer sox! My contribution, almost unfinished 'cause I only found this thread last Saturday, and my heat just went out (again) and I have to figure out how not to freeze. R L SUX (tm). But the main subject's covered OK.
The evolved Chryssalids resulted from earlier generations bringing surviving humans back to the hive, where the queen incorporated human DNA into a new breed of soldiers that have adapted some human structural features for greater strength, speed and increased size. The tentacles in the head act similar to a jellyfish's nematocysts (stinging cells), lashing out to embed parasitical organisms in living humans. These do not grow, but instead act as internal bioengineering factories, taking over the human DNA and hyper-mutating it to produce an evolved Chryssalid without the need for the hive mother.