The Reclassification That Made Opisthobranchia Disappear

For decades, nudibranchs and their relatives were classified under the subclass Opisthobranchia (後鰓類). But recent molecular phylogenetic studies have shown that this group is not monophyletic — meaning it doesn't include all descendants of a common ancestor.

What Changed?

The landmark paper by Jörger et al. (2010) and subsequent studies reorganized gastropod taxonomy. Opisthobranchia was dissolved, and its members were redistributed into new clades within Heterobranchia.

The New Classification

Under the new system, "sea slugs" are spread across multiple groups: Nudipleura (true nudibranchs and pleurobranchs), Euopisthobranchia (sea hares, bubble shells, pteropods), Panpulmonata (including some former opisthobranchs and land snails), and Sacoglossa (sap-sucking slugs).

What Does This Mean for Us?

For divers and enthusiasts, the practical impact is mainly in understanding that "sea slug" is not a formal taxonomic group but a convenience term. At SEASLUG.WORLD, we continue to cover all shell-less or reduced-shell gastropods, regardless of their current classification.

Taxonomy is a living science — classifications will continue to evolve as new evidence emerges. What matters most is accurate identification and documentation.