Lenticular Galaxy

Lenticular Galaxies  are a form of galaxy that classify as something between an elliptical galaxy and a spiral galaxy. Lenticulars, like spirals, are disks with a central bulge region. They may also possibly have a bar structure. Unlike spirals, however, they have no spiral arm formation and, like ellipticals, have little ongoing star formation and consist mainly of old stars. Lenticulars may contain significant amounts of dust in their disks, however. They are thought to have been formed as a result of galactic collisions between spiral galaxies. Roughly 20% of galaxies are lenticular.

Lenticulars are classified as S0 (unbarred) or SB0 (barred).

Lenticulars are likely to exhibit the same properties as spirals and ellipticals when it comes to habitability. Whether an individual lenticular is closer to an elliptical than to a spiral is up to the discretion of the worldbuilder.

Examples of lenticular galaxies include the Cartwheel galaxy, NGC 2787 and M84.

Worldbuilding in Practice
"The Ripple Galaxy, named for its ripple-like ring structure, is a barred lenticular galaxy and a ring galaxy, classified SB0(r). It is about 1800 parsecs across and contains roughly 30 billion stars. It is incredibly beautiful to observe and is the second largest object (apart from any nearby planets or suns) in the night sky when observed from Karnak, second only to Hathor, visible in most parts to the naked eye."