{"id":235,"date":"2012-05-14T21:13:06","date_gmt":"2012-05-14T19:13:06","guid":{"rendered":"https:\/\/opistobranquis.info\/nudibranquis-nudibranchianudibranquios-nudibranchianudibranchs-nudibranchia"},"modified":"2025-10-29T16:01:05","modified_gmt":"2025-10-29T15:01:05","slug":"nudibranchia","status":"publish","type":"page","link":"https:\/\/opistobranquis.info\/en\/guia\/nudibranchia\/","title":{"rendered":"Nudibranchia"},"content":{"rendered":"

Nudibranchs are a group of sea slugs that includes the traditional cladohepatic nudibranchs (aeolidaceans, arminaceans, and dendronotaceans), together with the enigmatic family Doridoxidae. All of them are characterized by having the anus located on the right side of the body and a more or less branched digestive gland.<\/p>\n

\"Felimare<\/div>
Felimare tricolor<\/em> by Enric Madrenas<\/center><\/span>

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The taxonomic history of nudibranchs (Nudibranchia Cuvier, 1817) is a paradigmatic example of how marine biology has evolved from an essentially morphological approach toward a phylogenetic synthesis that integrates anatomical, molecular, and ontogenetic data. Nudibranchs, traditionally included among the “opisthobranchs”, were for decades considered an order within this large group of marine gastropod mollusks characterized by the loss of the shell in the adult stage and the presence of external gills. This classical conception\u2014derived from nineteenth-century zoology\u2014remained current well into the twentieth century, when the first systematic morphological analyses began to reveal the internal complexity of the group and the lack of monophyly of the “Opisthobranchia”.<\/p>\n

The studies by Heike W\u00e4gele (2000), based on more than one hundred anatomical and histological characters, were decisive in consolidating the monophyly of Nudibranchia and establishing a primary division into two major lineages: Anthobranchia and Cladobranchia, distinguished by body morphology and gill arrangement. This basic framework dominated the group\u2019s systematics for almost two decades, until the advent of molecular techniques radically changed the way internal relationships among heterobranchs were understood.<\/p>\n

From the first molecular and transcriptomic studies of the 21st century (such as Karmeinski et al., 2021), it became clear that many traditional classifications were artificial or paraphyletic. Groups defined by superficial traits -such as body shape or the structure of cerata- proved to be heterogeneous, while other, seemingly unrelated lineages displayed unexpected phylogenetic affinities. In this context, the classical notion of Nudibranchia as a set of “shell-less opisthobranchs” lost its meaning, and attention shifted toward a phylogenetically coherent delimitation within the larger clade Heterobranchia.<\/p>\n

The work of Korshunova et al. (2025) represents, in this sense, a fundamental turning point. The authors propose an in-depth revision of nudibranch taxonomy based on a combination of detailed morphological data, ontogenetic observations, and molecular sequences. Their study denounces what they call “taxonomic pseudo-optimization”: a historical tendency to oversimplify classifications in order to fit them into rigid hierarchical models, thereby suppressing much of the group\u2019s genuine diversity.<\/p>\n

Korshunova et al. (2025) explicitly restrict the scope of the order Nudibranchia and reinstate five classical suborders that had been progressively merged or abandoned: Arminina, Tritonina, Dendronotina, Janolina, and Aeolidina. This reorganization restores phylogenetic coherence to the classification and recognizes the evolutionary independence of several lineages previously grouped under artificial names such as “Cladobranchia”. Particularly significant is the revision of the suborder Aeolidina, within which the authors identify ten clearly defined superfamilies and twenty-nine families, including two newly described ones (Chudidae fam. nov. and Hantazuidae fam. nov.). They also reinstate the superfamily Embletonioidea, whose position had long been debated in molecular studies.<\/p>\n

Although complex, this new classification offers a more realistic evolutionary framework and demonstrates that nudibranch diversity is far greater than previously assumed. The integrative approach of Korshunova et al. (2025) argues that only a joint analysis of morphology, genetics, and development can avoid distortions caused by taxonomic “optimization” and thus restore the group\u2019s true evolutionary richness. Ultimately, their work redefines Nudibranchia not as a remnant of the old “opisthobranchs”, but as a well-delimited clade within Heterobranchia, where the evolution of body forms and chemical defense systems has generated a diversity that, as the title of their paper suggests, is truly “endless and extraordinarily differentiated”.<\/p>\n

Nudibranchs, as a group, do not have a homogeneous body organization: the Aeolidioidea, Fionoidea, Flabellinoidea, and Proctonotoidea have elongated bodies and clusters of papillae called cerata<\/em> along both sides of the body. The Arminoidea have a more or less triangular body shape and live on soft bottoms. The Dendronotoidea and Tritonioidea possess elongated bodies with dendritic extensions on both sides, while the Doridoxoidea exhibit a body form similar to dorid nudibranchs, being dorsoventrally flattened.<\/p>\n

The systematic synopsis of nudibranchs according to Bouchet et al. (2017) and published at WoRMS is as follows:<\/p>\n

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Nudibranchia Cuvier, 1817<\/strong><\/p>\n