Is there a special symbol for instrumentation amplifier, to distinguish it from an opamp?
The simplest InAmps need a gain setting resistor and a reference pin like this: -



Now that doesn't look much like an op-amp to me. However, if it doesn't use a gain setting resistor (or maybe it's internally fixed) and, the reference pin is somehow internally dealt with you can use an op-amp symbol. 

However, I don't believe there are any InAmps that can internally deal with the reference pin other than by connecting it to midrail and this requires a 0V connection: -



Normally the 0V connection on R3 would exit the chip on a pin. 

You have to consider why this is so; An InAmp takes the difference in voltage levels between the two inputs, amplifies it by the gain factor and then references this amplified difference to (for want of better words) to a "reference pin".

This is what an InAmp does.