Glabella

Glabella adansoni, copyright Femorale.

Belongs within: Marginellinae.

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.

Glabella harpaeformis, copyright Joop Trausel and Frans Slieker.

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.

Glabella adansoni, copyright Rudolf Kapeller.

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.

Systematics of Glabella
Glabella Swainson 1840 [incl. Faba Fischer 1883, Phaenospira Hinds 1844]CC95
|--*G. faba (Linnaeus 1758)P61, L58 [=Voluta fabaP61, Marginella (Marginella sect. *Faba) glabellaCC95]
|--G. adansoni (Kiener 1834)CC95
|--G. aupouria (Powell 1937) [=Marginella (Glabella) aupouria]P61
|--G. bifasciata (Lamarck 1822) [=Marginella bifasciata]CC95
|--G. cracens (Dell 1956) [=Marginella (Glabella) cracens]P61
|--G. ergastula (Dell 1953) [=Marginella (Glabella) ergastula] P61
|--G. judithae (Dell 1956) [=Marginella (Glabella) judithae]P61
|--G. larochei (Powell 1932) [=Marginella (Glabella) larochei] P61
|--G. lucani (Jousseaume 1884)CC95
|--G. manawatawhia (Powell 1937) [=Marginella (Glabella) manawatawhia]P61
|--G. nodata (Hinds 1844) [=Marginella nodata, M. (*Phaenospira) noduta (l. c.)]CC95
|--G. otagoensis (Dell 1956) [=Marginella (Glabella) otagoensis]P61
|--G. prunum (Gmelin 1791)CC95 [=Marginella prunumCC95; incl. Voluta plumbea Sol. msC64]
|--G. pygmaea (Sowerby 1846) [=Marginella (Glabella) pygmaea]P61
|--G. pygmaeaformis (Powell 1937) [=Marginella (Glabella) pygmaeaformis]P61
|--G. tryphenensis (Powell 1932) [=Marginella (Glabella) tryphenensis]P61
`--G. vailei (Powell 1932) [=Marginella (Glabella) vailei]P61

*Type species of generic name indicated

References

[C64] Carpenter, P. P. 1864. Supplementary report on the present state of our knowledge with regard to the Mollusca of the west coast of North America. Report of the British Association for the Advancement of Science 33: 517–686.

[CC95] 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.

[L58] Linnaeus, C. 1758. Systema Naturae per Regna Tria Naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis revised 10th ed. vol. 1. Laurentii Salvii: Holmiae.

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.

[P61] Powell, A. W. B. 1961. Shells of New Zealand: An illustrated handbook 4th ed. Whitcombe and Tombs Limited: Christchurch.

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