No comb at all? Born that way or it could have gotten torn off. Maybe a pea comb or walnut. Alot of my hens have practically no comb, but very small peacomb....the stags though all have visible, even if pea.
I guess I it is called a pea comb, but my birds in the Amazon just had smaller ones I have seen here in the US. Here is a picture of one that I found that looks similar.