It didn't take long to discover that everything we thought we knew about Crabs was wrong. As soon as we saw their cities, their power plants and factories, their trains, planes and rockets, we jumped to the natural conclusion that they were sentient. Their technology meant they were clever; their space travel meant they were curious; their peaceful global community meant they were wise. It was, in retrospect, an obvious mistake.
The raw probe data suggested troubling divergence from the model. Nowhere was there any trace of writing. No labels or signs, no billboards or placards, no books or newspapers, no street names or numbers, not even any graffiti -- nothing. Likewise there was no radio communication, and the clicks they made themselves seemed to be more correlated with their level of arousal rather than their activity. There was no obvious hierarchy or leadership structure, and nothing that we could discern as coordinated decision making. It just looked like they all knew what they needed to be doing without having to ever ask.
Chemical language theory was invented to hold up the edifice of sentience. Crabs engage in trophallaxis, much like ants. While sharing food by mouth they probably also pass pheromones and other chemical signals. Why couldn't there be a pheromone grammar to express complex ideas? This chemical language might resist reduction to symbols, unlike our own very linear form of communication, so perhaps they never discovered writing or radio. Some even argued (those troubled by the Crab's tiny brain size) that the chemical signals might be a deeper type of "brain language" that would allow individual Crabs to share thoughts. They would solve problems collectively, like a kind of "hive mind."
Tantalizingly close, and yet wrong in every important respect.
When the E.O.Wilson dropped into the Crab system one of the survey team's very first tasks was to get samples of Crab saliva. They found it was easy to send probes to the surface; the Crabs entirely ignored both the starship and all their robot vehicles. Of course the samples were teeming with Lexocytes. It seemed like the answer. Lexocytes ("book cells") held about 10 times the genetic material of the Crabs themselves, and that would make an excellent media for expressing thoughts in a chemical language.
The name stuck, but the idea died quickly. Too many converging lines of evidence contradicted any plausible theory of Crab sentience. Once they worked out how Lexocytes worked in the Crab brain there was no going back. Crabs are semi-sentient at best, and more likely rate as entirely non-sentient. It might be more realistic to argue that the Lexocytes live a technological lifestyle using the Crabs as hosts, but the idea of a sentient microbe is beyond nonsense. Sometimes finding out you're wrong can be the most important conclusion.