Which term does NOT name one of the four main categories of galaxies in the Hubble classification scheme?

Name: Which term does NOT name one of the four main categories of galaxies in the Hubble classification scheme?
Brand: Quizplus
Rating: 4.7 (54 reviews)

Question

Quizplus · Accepted Answer

The Hubble classification scheme includes four main categories of galaxies: normal spirals (S), barred spirals (SB), ellipticals (E), and irregulars (I). "Starbursts" is not a main category, but rather a type of galaxy that is undergoing a burst of star formation activity.

Which Term Does NOT Name One of the Four Main