Plandin F.A., Temereva E.N. 2023. Anatomical data on Novocrania anomala (Brachiopoda: Craniiformea) support the “brachiopod fold” hypothesis // Invertebrate Zoology. Vol.20. No.3: 269–278 [in English].

Dept. of Invertebrate Zoology, Biological Faculty, Lomonosov Moscow State University, Moscow, 119991, Russia. E-mail:

doi: 10.15298/invertzool.20.3.01 Published online on August 26th, 2023

ABSTRACT. Brachiopoda is a phylum of marine benthic animals belonging to the Spiralia clade; however, their relationships with other spiralians and the origin of their unusual body plan remain unclear, even with the application of molecular genetics methods.

One of the major ideas on the origin of the brachiopod body plan is the “brachiopod fold” hypothesis, first proposed in 1991, and much developed since then. In its present content it implies that brachiopods derived from metameric ancestor by reduction of the number of metameres, and folding onto the ventral side. Thereby both valves – “dorsal” and “ventral” – turn out to be actually dorsal.

In the present study, we discuss the pros and cons of this hypothesis, and provide some additional data on the anatomy of Novocrania anomala adults, which is consistent with the “brachiopod fold” hypothesis. We have found traces of ancient “folding” in the form and co-localisation of lateral mesenteries and metanephridia. We also propose a general scheme of the evolution of the craniiformes’ body plan.

KEY WORDS: Brachiopoda, morphology, evolution, metanephridia, 3D reconstructions, “brachiopod fold” hypothesis.

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