Shining margins
Published 1 November 2023
Perhaps the first thing to be noticed about the margin snails of the Marginellidae is how shiny they are. Next is likely to be how brightly they are coloured; even those species where the shell is largely white are typically strikingly patterned. Margin shells must surely be among the contenders for the most aesthetically pleasing of all the neogastropods, and that’s a hard-fought contest indeed.
Marginellids get both their zoological and vernacular names from the thickened outer lip along their shell aperture. As seems to be the standard for neogastropods, the classification of marginellids has a complicated history, following the common trend of a shift from broader but less informative genera towards narrower but more contentious groupings. Though Glabella was first established as a generic name back in 1840, authors have disagreed whether to recognise its distinctiveness or treat it as a subgenus of the related Marginella (just to confuse matters, the species M. glabella is not a member of the genus or subgenus Glabella, but is instead the type species of Marginella). Coovert & Coovert (1995) recognised Glabella as distinguished by its biconic shell with strong axial costae, a distinct siphonal notch, strong plications on the columella, and distinct teeth on the outer lip. Molecular analysis by Fedosov et al. (2019), however, found Marginella and Glabella species intermingled within a single clade.
Whatever their relationship, both Marginella and Glabella reach their highest diversity around the coast of Africa, with a handful of Glabella species found in the Indo-Pacific (Coovert & Coovert 1995). Glabella species are found in relatively shallow waters, from the intertidal zone down to about 200 metres. In life, the animal is variously striped, streaked or spotted, with a broad foot (about 1.5 times as broad and long as the shell). Tentacles and siphon are also long.
Glabella and other species of the tribe Marginellini are united by the loss of the radula and associated buccal mass. I haven’t found any descriptions of the diet of Glabella species, but the related Marginella glabella is a predator or scavenger on a range of other marine animals such as gastropods and fish (Luque et al. 2012). Despite its lack of teeth, M. glabella is seemingly able to capture prey by paralysing it with toxin delivered through the long proboscis. Once the target has been rendered helpless, the voracious snail can presumably swallow it whole.
References
Coovert, G. A., & H. K. Coovert. 1995. Revision of the supraspecific classification of marginelliform gastropods. Nautilus 109 (2–3): 43–110.
Fedosov, A. E., M. C. Gutierrez, B. Buge, P. V. Sorokin, N. Puillandre & P. Bouchet. 2019. Mapping the missing branch on the neogastropod tree of life: molecular phylogeny of marginelliform gastropods. Journal of Molluscan Studies 85: 439–451.
Luque, Á. A., A. Barrajón, J. M. Remón, D. Moreno & L. Moro. 2012. Marginella glabella (Mollusca: Gastropoda: Marginellidae): a new alien species from tropical West Africa established in southern Mediterranean Spain through a new introduction pathway. Marine Biodiversity Records 5: e17.