Also look at the very Pokemon that turns into an octopus.
Case in point, another [bizarre] Generation II evolutionary masterpiece. Other than being aquatic creatures, the only thing Remoraid and Octillery have in common is that both were designed after firearms/artillery (i.e. handgun/pistol to siege weapon). Of course, they could've picked any fish in the sea, but decided to go with an octopus. Perhaps they were being cute and were going along the lines of real life remoras and octopi. Both have suction ability and tend to latch onto objects or other living creatures.
Generation II was great. But if you want to compare evolutionary logic with the other five generations, it had the most peculiar design choices.
I made the point about Mega Evolution because the only evolutionary line that has two final forms capable of Mega Evolving is the Ralts line (both Gardevoir and Gallade can Mega Evolve). You can't do much else with that line considering it's already at three stages. The only other diverging final evolved forms that can Mega Evolve are Slowbro and Glalie. Both have counterparts (Slowking and Froslass, respectively) who have significant similarities in design.
Pinsir and Heracross do not, other than the fact that both are bugs. Can't rule out the possibility that Game Freak will eventually run out of ideas and decide to throw in a pre-evolved form for Pinsir and Heracross, but I highly doubt it due to the significant differences between the two and the fact that they already opted to Mega Evolve them instead. It's like giving Kangaskhan the same treatment. Clearly there's a baby form there, but Game Freak has not designed a pre-evolved form of Kangaskhan and opted for Mega Evolution instead.