Located within the informal group “Lower Heterobranchia”, the Architectonicoidea form a group of sea snails, with the category of superfamily, with spirally coiled shells, often ornamented, which are categorized as heterobranchs by heterostrophy, sperm morphology and osphradium, as well as by certain genetic traits.

Heliacus fallaciosus @ Eivissa, Spain May, 2022 by Joan Pereyra

Most of them are very small in size, with benthic habits, living under rocks in the subtidal, but also in specialized microhabitats. Its phylogenetic classification was still unresolved in 2018 but there are several studies ongoing.

The order Architectonicida (equivalent to the Superfamily Architectonicoidea sensu lato) share the above-mentioned characteristics of being benthic snails with a very flattened spiral shell, which are usually pigmented brown and ornamented. They have a wide, bifid snout and foot, and a pair of broad, elongated tentacles on the head. It contains 3 families worldwide, all present in European waters.

Taxonomy of Architectonicoidea

  • Mollusca (Phylum)
    • Gastropoda (Class)
      • Heterobranchia (Subclass)
        • “Lower Heterobranchia” (Infraclass)
          • Architectonicoidea (Superfamily)
            • Architectonicidae (Family)
              • Basisulcata (Genus)
              • Heliacus (Genus)
              • Philippia (Genus)
              • Pseudotorinia (Genus)
              • Psilaxis (Genus)
              • Solatisonax (Genus)
            • Mathildidae (Family)
              • Mathilda (Genus)
            • Omalogyridae (Family)
              • Ammonicera (Genus)
              • Omalogyra (Genus)

Species of Architectonicoidea reported in the Mediterranean Sea o around the Iberian Peninsula:

Heliacus fallaciosus @ Eivissa, Spain May, 2022

Heliacus fallaciosus


    Baeumler N, Haszprunar G, Ruthensteiner B. 2008. 3D interactive microanatomy of Omalogyra atomus (Philippi, 1841) (Gastropoda, Heterobranchia, Omalogyridae). Micromolluscs: Methodological Challenges - Exciting Results: Proceedings from the Micromollusc Symposium of the 16th Unitas Malacologica World Congress of Malacology. 1:101–118. Available from ://WOS:000278006900006.
    Dinapoli A, Klussmann-Kolb A. 2010. The long way to diversity - Phylogeny and evolution of the Heterobranchia (Mollusca: Gastropoda). Molecular Phylogenetics and Evolution. 55(1):60–76.
    Healy JM. 1993. Comparative Sperm Ultrastructure and Spermiogenesis in Basal Heterobranch Gastropods (Valvatoidea, Architectonicoidea, Rissoelloidea, Omalogyroidea, Pyramidelloidea) (Mollusca). Zoologica Scripta 22(3):263-276.
    Tiberi N. 1872. Generi e specie della Fam. Solariidae, viventi nel Mediterraneo e fossili nel terreno pliocenico italiano. Bullettino Malacologico Italiano. 5:31–48.

    Bibliography based on the works by Steve Long, 2006. Bibliography of Opisthobranchia 1554-2000 and Gary McDonald, 2009. Bibliographia Nudibranchia, with later updates from other resources.