Tricolia pullus pullus, copyright H. Zell.

Belongs within: Vetigastropoda.

Tricolia: fluorescent seashells
Published 2 November 2020
Tricolia pullus, copyright Ar rouz.

Search among patches of seaweed along the shores of Africa, Australia or warmer parts of Eurasia and you may be able to find represents of the marine gastropod genus Tricolia. Tricolia are small shells, less than a centimetre in height, with shiny shells that may be smooth or spirally ribbed. Most species have a moderately high spire and an ovate shape but some are lower and more globose (Knight et al. 1960). The shell may or may not have an umbilicus, and there is a calcareous, externally convex operculum. Tricolia belongs to the Phasianellidae, commonly known as pheasant shells, presumably in reference to the bold, intricate colour patterns of many species. Species of Tricolia and the closely related genus Eulithidium, which replaces it in the Americas, have shell pigments containing porphyrin that fluoresce under ultraviolet light (Vafiadis & Burn 2020). Over forty species of Tricolia are currently recognised with the highest diversity in southern Africa (Nangammbi et al. 2016). However, the taxonomy of the genus has historically been confused due to polymorphic species being named multiple times; it is possible that at least some of the apparent African diversity is an artefact of the genus being largely unrevised in that region. An analysis of some of the southern African taxa by Nangammbi et al. (2016) found that some ‘species’ could not be distinguished genetically. They were, nevertheless, distinct geographically and the authors suggested that they may be variants of a single species responding to different environments.

Variants of Tricolia kochii, copyright Brian du Preez.

Like other members of the Vetigastropoda (the clade containing most of what used to be called the ‘archaeogastropods’), Tricolia species have a simple life cycle without an actively feeding planktonic larva. The basic mode of reproduction is by broadcast spawning with separate males and females releasing gametes into the water column. After fertilisation, a brief non-feeding planktonic phase is nourished by yolk from the egg before the larva settles. The brevity of this phase is reflected by the resultant form of the protoconch which accounts for less than an entire whorl. In the Indo-West Pacific species T. variabilis, the male is smaller than the female and sits directly on her, waiting to fertilise her eggs as they are laid as gelatinous capsules rather than freely broadcasted. A temperate Australian species, T. rosea, takes things a step further as the female broods embryos (up to nearly fifty at a time) within the cavity of the last shell whorl (Vafiadis & Burn 2020). How the eggs are actually fertilised remains unknown but all embryos within a brood are about the samesize and stage of development, indicating a single fertilisation event; perhaps males associate with females as in T. variabilis. After the young pheasant shells hatch or settle, they initially feed on diatoms and other microalgae until they eventually grow enough to move onto the seaweed fronds that will comprise their adult diet.

Systematics of Tricolia
<==Tricolia Risso 1826BR05 (see below for synonymy)
|--T. (Tricolia)KC60
| |--*T. (T.) pullus (Linnaeus 1758)KC60 (see below for synonymy)
| `--T. (T.) variegataKC60
|--T. (Aizyella Cossmann 1889)KC60
| `--T. (*A.) suessoniensis Deshayes 1863 [=Phasianella suessoniensis, P. herouvalensis Cossmann 1889]KC60
|--T. (Eotricolia Kuroda & Habe 1954)KC60
| `--T. (*E.) megastoma (Pilsbry 1895) [=Phasianella megastoma]KC60
|--T. (Hiloa Pilsbry 1917)KC60
| `--T. (*H.) thaanumi (Pilsbry 1917) [=Phasianella thaanumi]KC60
`--T. (Phasianochilus Cossmann 1918)KC60
`--T. (*P.) turbinoides (Lamarck 1804) [=Phasianella turbinoides]KC60

Tricolia incertae sedis:
T. affinisBC01
|--T. a. affinisBC01
`--T. a. beaui Robertson 1958BC01
T. compta (Gould 1855)O27 (see below for synonymy)
|--T. c. comptaO27
`--T. c. punctulata (Carpenter 1865) [=Phasianella compta punctulata]O27
‘Eucosmia’ cyclostomaC64
T. fordiana (Pilsbry 1888)BC01 (see below for synonymy)
T. gabiniana (Cotton & Godfrey 1938)W93
T. laubrierei (Cossmann 1888)TTE93
T. macleani Marincovich 1973BC01
T. pulloides (Carpenter 1865) [=Phasianella (Tricolia) pulloides]O27
|--T. p. pulloidesO27 [=Phasianella compta var. pulloidesC64]
`--T. p. elatior (Carpenter 1865)O27 [=Phasianella pulloides elatiorO27, P. compta var. elatiorC64]
‘Eucosmia’ punctataC64
T. rosea (Angas 1867)W93 [=Pellax roseaF26]
T. thalassicola Robertson 1958BC01
T. tomlini (Gatliff & Gabriel 1921) [incl. T. irritans Thiele 1930]W93
T. variabilis (Pease 1861)W93 [incl. T. gregaria Laseron 1955W93, T. virgo Angas 1867W93, Pellax virgoF26]

Tricolia Risso 1826BR05 [=Eudora Gray 1852 non Péron & Lesueur 1810KC60, Steganomphalus Harris & Burrows 1891KC60, Tricoliella Monterosato 1884KC60; incl. Chromotis Adams & Adams 1863KC60, Eucosmia Carpenter 1864 non Stephens 1831KC60, Usatricolia Habe 1956KC60]

Tricolia compta (Gould 1855)O27 [=Phasianella (Tricolia) comptaO27; incl. P. affinisC64, P. capensisC64, P. concinnaC64, P. elongataC64, P. intermediaC64, P. pulchellaC64, P. compta var. punctulataC64, P. tenuisC64, P. tessellataC64]

Tricola fordiana (Pilsbry 1888)BC01 [=Phasianella fordianaBC01; incl. T. elachista Melvill 1901W93, T. minima Melvill 1896W93]

*Tricolia (Tricolia) pullus (Linnaeus 1758)KC60 [=Turbo pullusKC60, *Eudora pullusKC60, Phasianella pullaC64, *Steganomphalus pullusKC60, *Tricoliella pullusKC60]

*Type species of generic name indicated


[BR05] Bouchet, P., & J.-P. Rocroi. 2005. Classification and nomenclator of gastropod families. Malacologia 47 (1–2): 1–397.

[BC01] Boyko, C. B., & J. R. Cordeiro. 2001. Catalog of Recent type specimens in the Division of Invertebrate Zoology, American Museum of Natural History. V. Mollusca, part 2 (class Gastropoda [exclusive of Opisthobranchia and Pulmonata], with supplements to Gastropoda [Opisthobranchia], and Bivalvia). Bulletin of the American Museum of Natural History 262: 1–170.

[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.

[F26] Finlay, H. J. 1926. A further commentary on New Zealand molluscan systematics. Transactions and Proceedings of the New Zealand Institute 57: 320–485.

[KC60] Knight, J. B., L. R. Cox, A. M. Keen, R. L. Batten, E. L. Yochelson & R. Robertson. 1960. Gastropoda: systematic descriptions. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt I. Mollusca 1: Mollusca—General Features, Scaphopoda, Amphineura, Monoplacophora, Gastropoda—General Features, Archaeogastropoda and some (mainly Paleozoic) Caenogastropoda and Opisthobranchia pp. I169–I331. Geological Society of America, and University of Kansas Press.

Nangammbi, T. C., D. G. Herbert & P. R. Teske. 2016. Molecular insights into species recognition within southern Africa’s endemic Tricolia radiation (Vetigastropoda: Phasianellidae). Journal of Molluscan Studies 82: 97–103.

[O27] Oldroyd, I. S. 1927. The Marine Shells of the West Coast of North America vol. 2 pt 3. Stanford University Press: Stanford University (California).

[TTE93] Tracey, S., J. A. Todd & D. H. Erwin. 1993. Mollusca: Gastropoda. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 131–167. Chapman & Hall: London.

Vafiadis, P., & R. Burn. 2020. Internal embryonic brooding and development in the southern Australian micro-snail Tricolia rosea (Angas, 1867) (Vetigastropoda: Phasianellidae: Tricoliinae). Molluscan Research 40 (1): 60–76.

[W93] Wilson, B. 1993. Australian Marine Shells vol. 1. Prosobranch Gastropods. Part One. Odyssey Publishing: Kallaroo (Western Australia).

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