Project 2877: J. A. Goodheart, S. Bleidissel, D. Schillo, D. L. Ayres, A. Preisfeld, E. E. Strong, A. G. Collins, M. P. Cummings, H. Waegele. 2018. Comparative morphology and evolution of the cnidosac in Cladobranchia (Gastropoda: Heterobranchia: Nudibranchia). Frontiers in Zoology. 15:43.
Specimen: Dondice occidentalis (USNM:1276036)
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A number of shelled and shell-less gastropods are known to use multiple defensive mechanisms, including internally generated or externally obtained biochemically active compounds and structures. Within Nudipleura, nudibranchs within Cladobranchia possess such a special defense: the ability to sequester cnidarian nematocysts – small capsules that can inject venom into the tissues of other organisms. This ability is distributed across roughly 600 species within Cladobranchia, and many questions still remain in regard to the comparative morphology and evolution of the cnidosac – the structure that houses sequestered nematocysts (called kleptocnides). In this paper, we describe cnidosac morphology across the main groups of Cladobranchia in which it occurs, and place variation in its structure in a phylogenetic context to better understand the evolution of nematocyst sequestration.

Overall, we find that the length, size and structure of the entrance to the cnidosac varies more than expected based on previous work, as does the structure of the exit, the musculature surrounding the cnidosac, and the position and orientation of the kleptocnides. The sequestration of nematocysts has originated at least twice within Cladobranchia based on the phylogeny presented here using 94 taxa and 409 genes.

The cnidosac is not homologous to cnidosac-like structures found in Hancockiidae. Additionally, the presence of a sac at the distal end of the digestive gland may have originated prior to the sequestration of nematocysts. This study provides a more complete picture of variation in, and evolution of, morphological characters associated with nematocyst sequestration in Cladobranchia.

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Article DOI: 10.1186/s12983-018-0289-2

Project DOI: 10.7934/P2877,
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    Authors' Institutions

    • National Museum of Natural History, Smithsonian Institution

    • University of California Santa Barbara

    • University of Maryland

    • University of Wuppertal

    • Zoologisches Forschungsmuseum Alexander Koenig

    • Smithsonian Institution


    member name taxa specimens media
    Jessica Goodheart
    Project Administrator
    Sabrina Bleidißel
    Allen Collins
    Michael Cummings
    Dorothee Schillo
    Ellen Strong
    Heike Wägele
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    Document downloads3Data Matrix of Cnidosac Details (1 download); Data Matrix of Presence/Absence of Distal Sac and Kleptocnides (2 downloads);
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