Incorrect.(Psi)SeveredHead said:Abilities such as rend are no longer considered Ex abilities. They are considered natural abilities. For obvious reasons, they are not going to errata every other monster in the Monster Manual.
The spell specifically says that you don't get any extraordinary abilities. This has also been confirmed by the Sage.
It's up to the DM if you get the two (constrict and low-light vision) specifically mentioned, but they were probably included by mistake - see below.
<This page> contains several Sage answers to polymorph questions. (Note that he is mistaken about constrict not being extraordinary.)
Also see <Psionics Handbook errata> (Version 05302002) where all extraordinary abilities used as examples have been removed. (Originally the Polymorph Self in the Psionics Handbook was essentially identical to the errataed version in Tome and Blood.)