Some critical notes on the name change of Lotoria perryi (Emerson & Old, 1963) into Lotoria triangularis (Perry, 1811) (, )

by M.C. van Veen, 25 September 2020

Introduction

Septa triangularis Perry, 1811 has been the object of discussion several times. Dodge (1957) suggested that Perry's was femorale (Linnaeus, 1758), and Clench & Turner (1957) synonymised it also with the same species. Emerson & Old (1963) proposed triangularis to be a taxon inquirendum, because a type specimen was not available.

However, they leaned toward the possibility that Perry's species could be a juvenile specimen of their new species Cymatium perryi, which is now placed in the Lotoria: Lotoria perryi (Emerson & Old, 1963).

Even though all of these authors were well aware of the distribution range that was given by Perry, they most likely ignored his description because of its shortness and its "non-diagnostic" character. Authors started to analyse Perry's illustration instead of his description, and all of their suggested species did not match regarding their distrubution range.

There is however one species that matches perfectly with both Perry's description as well as his illustration.

Perry's description and illustration

figure 1.

Perry described this species as follows:

No. 6. Septa triangularis. Shell reddish brown, variegated with white and dark brown marks; its angular cheek, will easily distinguish it from the rest of its congeners. It is a native of the Southern Ocean. Analysis

First of all, it must be noted that the drawing provided by Perry is not entirely accurate, it is an artist's impression that is close to realism, but it lacks detail and consistency on several points.

Nevertheless, Perry’s description makes a strong emphasis regarding identification: the angular cheek, or its funnel shape, sets it apart from all other species. The reddish brown colour is of less concern, because several species meet that criterium. Another important detail is its distribution range: the Southern Ocean.

Nowadays this is the ocean around the Antarctic, with 60 degrees south latitude as its northern limit. In Perry's time, the early 19th century, the northern boundary of the Southern Ocean would have been different.

According to the definition of 1919 the Southern Ocean stretched northward to South Africa and included the Great Australian Bight. This was published in the first edition of 'Limits of Oceans and Seas,’ by the International Hydrographic Bureau in 1928. Figure 2 shows this world map, which is provided by the NOAA Central Library Historical Collections, uploaded to Wikimedia Commons https://commons.wikimedia.org/wiki/File:Limit_of_Oceans_and_Seas_-_1st_Edition_-_1928.jpg

figure 2. World map of the Limits of Oceans and Seas, by the International Hydrographic Bureau, first edition, 1928. Discussion

Septa triangularis has now become synonymous to Lotoria perryi, and the name of this species has been changed into Lotoria triangularis (Perry, 1811). In WoRMS (World Register of Marine Species) this record was last updated in March 2019. http://www.marinespecies.org/aphia.php?p=taxdetails&id=1332344

The species Lotoria perryi, as described by Emerson & Old, does not correspond with Perry’s Septa triangularis. Not only regarding its morphology, but also its distribution range is different: Southern India and Sri Lanka are not even near the Southern Ocean. The motivation behind the change in the record on WoRMS is unclear and should be questioned.

Perry's species can be interpreted in several ways, and Dodge (1957) made an interesting remark when he mentioned that Bonanni (1709) gave the Caribbean species (Linnaeus, 1758) the pre-Linnean name Murex triangularis This is Bonanni's species number 291 which is also clearly illustrated.

This however doesn't automatically mean that Bonanni's Murex triangularis is the same as Perry's Septa triangularis. Homonyms were common in 18th and 19th century literature, because relatively isolated malacologists worked independently of each other and came up with identical names but for different species. It should also be mentioned that Perry used the genus Septa instead of Murex, and in itself this is already enough to question the synonymy.

The fact that Bonanni's and Perry's 'Triangularis species' both belong to the family Cymatiidae and are both 'classic Cymatiums,' might be a consequence of the fact that a number of species in the Cymatiidae produce shells that are triangular in the juvenile or in the adult stage. Naming a triangular or funnel-shaped species 'triangularis' can become rather obvious.

There is however a species that fits both description and illustration, and that is Cymatium ranzanii (Bianconi, 1850). Its distribution range is South Africa and Mozambique, stretching far north toward the coasts of the Arabian Sea. In essence this corresponds with the Southern Ocean, as the South African waters were considered a part of it back in the early 19th century.

Morphologically this species also matches with Perry’s strongest identification key: the angular cheek.The angular shape of the siphonal canal, the outer edge, and the parietal area, matches the illustration. Also the long, continuous brown-white checkered varix on the outer edge (the cheek) is a feature seen in Cymatium ranzanii but not in the much more undulating outer edge of adult Lotoria perryi. Two photographs from Wikimedia Commons show this difference in figure 3.

However, juvenile specimens of Lotoria perryi still have a fairly straight outer edge, as Emerson &Old (1963) showed with their paratype. It is possible that this similarity created the impression that Septa triangularis and Lotoria perryi are synonymous. The only issue that remains is the discrepancy in the distribution range of both species. figure 3.

Left. Cymatium ranzanii (Bianconi, 1850). Locality: Mozambique. Provenance: Jan Delsing on Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Cymatium_ranzanii,_underside_-_BioLib.jpg Right: Lotoria perryi (Emerson & Old, 1963). Provenance: user Shellnut on Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Lotoria_perryi.jpg

If Perry's description of Septa triangularis would get validated the way it did with Lotoria perryi, even in absence of a type specimen, then one could argue for the substitution of the name Cymatium ranzanii, since Perry holds seniority over Bianconi.

Literature next page. References

Bianconi, J.J. (1850) - Specimina Zoologica Mosambicana, Fasciculus IV, Memorie della Accademia delle Scienze dell'Istituto di Bologna, Tome 3, pp 3-18, Plate 3.

Bonanni, P. (1709) - Musaeum Kircherianum, 522 pp., 412 illustrations.

Clench, W.J. & Turner, R.D. (1957) - The family Cymatiidae in the western Atlantic, Johnsonia, Harvard University, vol. 3, pp. 189-244, pls. 110-135.

Dodge, H. (1957) - A historical review of the mollusks of Linnaeus, Part 5, The genus Murex of the class Gastropoda, Bulletin of the American Museum of Natural History, vol. 113, pp. 73-224.

Emerson, W.K. & D'Attilio, A. (1962) - Remarks on Triton ranzanii Bianconi (, Gastropoda), American Museum Novitates, no. 2108, 8 pp., 4 figs.

Emerson, W.K. & Old, W.E. (1963) - A new subgenus and species of Cymatium (Mollusca, Gastropoda). American Museum Novitates, no. 2137: 1-13.

Linnaeus, C. (1758) - Systema Naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Editio decima, reformata [10th revised edition], vol. 1: 824 pp

Perry, G. (1811) - Conchology, or the natural history of shells: containing a new arrangement of the genera and species, illustrated by coloured engravings executed from the natural specimens, and including the latest discoveries. 4 pp., 61 plates. London.