A preliminary scheme for grouping peculiar galaxies was given in [4, 5]. Independently, Arp and Madore [6] give 24 natural groups listed in Table A. Karachentsev [59], on the other hand, suggests a much more modest morphological classification for non-equilibrium systems as outlined in Table B. Because of the very nature of peculiar galaxies none of these systems has found wide application.

Ring galaxies, as a subset of peculiar and interacting galaxies, are widely recognized [27], sub-divided and internally classified as in [185], as explained in Table C; or as outlined in [43] and Table D; while [41] presents a report on classifying ring galaxies according to the morphology of their nuclear component alone. ``Ringed'' galaxies, on the other hand, are discussed in detail in [19]; shells and rings around galaxies are reviewed in [8]; warped disks and inclined rings are the topics in [22].