Marginella pseudosebastiani Mattavelli, 2001.
Statements on the "Complex", with particular respect to
Marginella sebastiani Marche-Marchad & Rosso, 1979.
Marginella pseudosebastiani, recto & verso, 47,3 mm length, sintype.
Introduction. In 2001, on the basis of 30 sintypes about, a new species has been described as Marginella pseudosebastiani [Flavio Mattavelli, Malacologia Mostra Mondiale (magazine, via Adriatica Nord, 240 - 63012 - Cupra Marittima - AP - Italy), n°34, September 2001, pages 03-08, only in Italian language]. The species was located in Mauritania, 60-90 m depth.
Owing to shell affinity, the species Marginella glabella (Linneus 1758), Marginella sebastiani Marche-Marchad & Rosso 1979 and Marginella pseudosebastiani were included in a "(Marginella) glabella & sebastiani Complex", linking to the Complex M. desjardini Marche-Marchad 1957, M. goodalli Sowerby 1825, M. irrorata Menke 1828 and the "hybrid forms".
The terms “hybrid” and “albino” were used, and
are used only with a morphological purpose.
Comparative description. In order to distinguish M.
pseudosebastiani it is essential to notice the simultaneous presence of
several evident morphologic features:
- length 40/64 mm (min/max. length of my 30 homogeneous sintypic specimens of new species)
- dark brown bend always present under the suture, always with very evident whitish axial subsutural flames (these axial flames are always clear in M. glabella & M. desjardini too, but not in M. sebastiani Marche-Marchad & Rosso 1979: it is important to note that true M.sebastiani can show axial subsutural whitish small flames, that however in many cases are not clearly evident, or even absent in most forms related to its holotype)
- very light carnation pink bottom colour (the bottom colour of M. pseudosebastiani is lighter than typical M. sebastiani)
- two evident dark bends only on the body whorl (the dark bends of M. pseudosebastiani are always less evident than the dark bends of M. desjardini, and those of M. pseudosebastiani are always more evident than those of typical M. sebastiani)
- several whitish spots, about 1-2 mm diameter, clearly spread in a large quantity on the body whorl, generally without superposition, sometimes aligned (these spots are smaller and more numerous than the relatively few marks of the typical M. sebastiani, that is studded with big punctiform marks, 2-3 mm diameter about; besides on M. pseudosebastiani the spots are never very close and confused as on M. glabella, where the spots are mostly superimposed)
- on M. pseudosebastiani (but also in M. sebastiani) you can find some spots also in light bends, which never happens in M. desjardini, where the marks, often changed into light long marks, can be found only in the area of the dark bends
- the shape of shell of M. pseudosebastiani is usually lengthened nearly as in M. desjardini, little more than in M. sebastiani, much more than in M. glabella (but some small specimens of M. pseudosebastiani can be confused with special forms of M. glabella)
- whitish margin inner side with feeble crenation from 0 till 19 denticles never striking (often there are tracks of denticles distributed along the whole margin), never concentrated (on the contrary the denticles are sinusoidally protruding and concentrated in the adult specimens of M. desjardini).
You must not consider a single feature, but you must consider the whole of them.
Gallery. In biology a species could be
define also when it is not easily distinguishable, and vice versa an
animal can be distinguished but not biologicaly distinct from its similars.
I do not know the DNA test for M. pseudosebastiani, but it does not touch the high “conch-logic” interest, especially at amatorial level. Passion is above all stimulate when watching a shell the collector does not succeed in morphologic classification. So the ideas can change depending of the collector culture or knowledge, can he be a lumper or a splitter more or less expert.
For this reason i decide to share this
Not all the pictures are mine, some are
taken from internet with a didactic purpose only for scientific reasons.
Marginella sebastiani, 42 mm length, almost “typical” morph, picture taken on a Singapore site. In the buccal view note the crenated margin and the “typical great” spotting of the livery (spotting already reduced in the dorsal view).
Morphologic notes. Sometimes, to abbreviate, I indicate Marginella pseudosebastiani as P, and Marginella sebastiani as S. The margin of P usually is smoother of S. However the presence of the dentation on the margin alone is never determining for the identification. There are S with the completely smooth margin.
It is difficult to separate P from S only by watching the dots of the shell. In my opinion the white spots (generally smaller in P) are not determining by themselves. The configurations of the dots sometimes do not show the "typical" configurations. There are atipical P with great dots.
pseudosebastiani with wide spots, recto and verso, picture
taken on eBay with the wrong name of M. desjardini, 41 mm, trawled at 300
m, Mauritania. The nomenclature is incorrect because in M. desjardini
there are no spots in the light stripes, instead in the picture spots are
present (bigger than the typical M. pseudosebastiani), of course without
considering the flash reflexes. Generally in M. desjardini the dark
stripes are darker, the over sutural pale stripe seams nearly white, the lip is
not smooth as in the picture.
The holotype of M. sebastiani Marche-Marchad & Rosso 1979 had few very great clear points. However there are also atypical M. sebastiani with small and numerous clear points (which are similar to those of the typical M. pseudosebastiani), as you see in the following photo, where axial subsutural flames are absent.
Atypical M. sebastiani, with small and numerous clear points.
The discriminating factor between P&S is the presence of white axial subsutural flames.
In M. pseudosebastiani they are always present and are crammed and subparallel to the axis of the shell. In M. sebastiani they are usually absent or, when they seldom appear, they are like isolated prolonged stains.
The flames exist commonly also in M. glabella, and in M. desjardini, but these species are different from P & S, for different patterns.
The real problem is with intermediate specimens P & S, for example see picture in Harry G. Lee's section.
Also see the pictures in Quick reference guide.
Distribution. The correct geographic distribution of molluscs is always fundamental. I reconfirm that the distribution area of Marginella pseudosebastiani is only "Mauritania", as defined below. I found that confirmation is on line, in specialized Web sites about West Africa shells (see links page).
better Cap Vert, is a board line between two
different marine zoogeographic provinces:
1. In the North of Cap Vert an almost temperate area with high salinity and cold sud-west currents; to semplify I call this Senegal's portion "Mauritania", including true Mauritania also.
2. In the South of Cap Vert an hotter region with moderate salinity and warm sud-east currents ; I call this Senegal’s portion "Guinea", I mean with Guinea Bissau and Guinea Conakry, also this “Guinea” is homogeneous since Niger delta, that is the cause of a low water salinity, introducing a new ecological boundary. Do not confuse this area with the Equatorial Guinea in the South-East.
Marginella sebastiani can be found surely and typically from South of Cap Vert as far as Conakry and Bissau "Guinea" (not Equatorial Guinea), but specimens are found in South of "Mauritania" also (Senegal, not including true Mauritania). Marche-Marchad & Rosso chose as holotype of M. sebastiani a specimen from Senegal (“Cap Vert Peninsula”), coloured, without whitish subsutural axial flames, with wide light spots, shell not very elongated, but with the buccal margin armed with a lot of denticles, as many typical specimens of “Guinea”.
Incidentally, in Cap Vert Islands, species of the “glabella & sebastiani complex” are not found, because of the too cold waters (Antonio Guerreiro, personal comunication).
It should be investigate also on the batimetric distribution of all the complex, but it is so hard!
Geographical discussion. On the market today, M. pseudosebastiani is rarer than M. sebastiani, but I believe that both species live common, respectively the first in the temperate waters of “Mauritania” and the second in the warm waters of “Guinea”, even if the living area of M. sebastiani can be found in the North of Senegal (to Mauritania), not with typical populations, but principally with hybrids S & P, or presumable ones, as before in Harry G. Lee's section, for rare reverse coiled specimens. There are also hybridations of S with M. glabella, and P with M. glabella.
P & S seam to be actually two “sister” species highly hybridable, without being the same biological species, and also not to be two geographical subspecies of the same biological species. Note that, in case of P or S populations, every morphology, extreme or intermediate, has a geographic location pratically unic. P & S are the furthermost limits of a chain, that have no possibility of interbreeding between themselves in most of cases. Where there is a species there is not the other, generally; sometimes the intermediate rings can form “hybrid” populations (with intermediate morphologial characteristics) of homogeneous and fertile individuals; for this reason it is discussible to define them as hybrids. Every single population actually presents characteristics sometimes more P or more S, without raeching the total mixing of the two morphology in all the individuals of the population, in the same geographical area.
North of Cap Vert, with precision in Kayar, there should be the biggest specimens of P, in simpatry with M. desjardini (Marcel Pin, personal communication; oddly, he spoke about some specimens called S, with the P morphology instead). I cannot exclude also a probable hybridation of P versus M. desjardini, north Cap Vert. This hybridation could be the cause of the growth of the sizes of the shells of P.
On the other hand, as in the following picture, from e-Bay, there are hybridations (but not hybridations of P) with M. desjardini also south Cap Vert. The provenience of the big specimen, in e-Bay wrongly named: "Marginella desjardini", 57mm, F++/Gem, Casamanche, is south Cap Vert, but the specimen is not completely M. desjardini (in M. desjardini there are no spots in the light stripes, instead in the picture big spots are present, typical of S). It not could be a "hybrid" P/S for the presence of sinusoidal protuberance of the lip, distinctive of M. desjardini.
In my opinion it is a "hybrid" M. sebastiani/desjardini.
At the end, in “Guinea” are found only M. sebastiani, and in the South of Senegal the most striking M. sebastiani (in my opinion because of hybridations with the best M. desjardini, and sometimes with M. goodalli, instead in “Guinea” there should not be hybridations between P & S).
If P & S were two flowing subspecies, statistically, a gradually intermediate mutant big population shoul appear in a wide intermediate living area, while actually there is a morphologic separation in two different big population only with some hybrid population, or single hybrids, in the boundary area between the 2 endemicity zones. It is as there was a clepsydra-like distribution. By clepsydra distribution I have deduced that P&S really are two different species.
“Albinos”. In M. glabella, "albinos" sometimes are apparently common, little size, stocky, in determinate places ("Mauritania"). On the contrary, I have not found albino specimens that can be related to M. sebastiani or to M. pseudosebastiani surely, but they could exist. I have notice this following picture of Roger Le Béon about two marginellas of the studied complex.
On the left an unique elongated specimen completely with an uniform greenish straw colour, 54 mm length, Cote d'Ivoire (!), 1,86 lengthening. The lengthening is like M. desjardini, but the shell outline looks like P/S. It should be also a strange variety, in strange locality, of M. glabella, species where albinos are known, also in shells not so elongated as in P/S.
On the right another specimen of uncertain nomenclature, perhaps a hybrid M.glabella/ M.sebastiani, or atypical M. sebastiani, 53 mm length, Sénégal, 1,79 lengthening, with too little subsutural flames, coulored as M. sebastiani.
M. glabella is certainly the species that presents greatest variability, generally associated with a smaller size than P&S, and alternate in geographic distribution. See the article "Universo lumperia".
Geographic exceptions. I propose an interesting particular case, the “almost-albino” specimen n° 1488 of the Web site FIRAMA.
Specimen n° 1488. The anomaly of the great clear spots, perhaps a tendency to albinism, is no doubt the worthiest morphologic characteristic. So this specimen, 52 mm length, may be a very anomalous Marginella pseudosebastiani or a true hybrid P/S. In my opinion this specimen is rare, both for the morphology and the place of origin.
The most amasing biological characteristic is that the shell seems to come from the Guinea Bissau, Geba River, trawled 50 m: it would be like finding a white bear in Italy. It is possible a hybridation M.sebastiani/M.desjardini too, but very strange morphologically: it is too clair, the outer lip is smooth, without sinusoidal protuberance of the central denticles.
Conclusion. In the "Complex", with M. desjardini, P&S and M. glabella, there are 4 basic morphologies which are different but between themselves they are intermediate, as if the basic morphologies were set each at the vertexes of a tetrahedron. Biological science today is based no longer on morphology, but without morphology not even Biology can exist. How to identify the intermediate cases? It would be necessary to find the soft parts of the molluscs, and, besides a direct anatomical comparison, the scientist could make the DNA analysis, or some other discriminating biological analysis. For shell collector the game could not be worth the candle.
Dott. Ing. Flavio Mattavelli.
Via Serbelloni, 67
20064 - Gorgonzola - MI - Italy. E-mail: firstname.lastname@example.org
Update 11/2006. Top.
Il sito a giugno 2020 è composto da 41 pagine, raggruppate in 4 Sezioni, da dove potete risalire alle singole pagine:
Sez. Macchine (7 pag.). Panoramica di alcune macchine costruite presso la ditta Cavalleri Mattavelli Sas., dove ho lavorato per oltre 40 anni.
Sez. Aeromodellismo (16 pag. solo in italiano). Parentesi ludica su aeromodelli non convenzionali in cartoncino, canard e tuttala, con studi di aerodinamica amatoriale.