Notes on Cymbium glans and Cymbium coenyei (Gastropoda, Volutidae) by M.C. van Veen, November 2020 Introduction A few months ago a vendor in Italy sold me a very large shell of the genus Cymbium. At first glance it seemed the photo of the shell depicted a gerontic Cymbium glans (Gmelin, 1791). Considering its size (323 mm) and its locality (Cameroon) it would be hard to imagine it could be any other species than Cymbium glans, which is known to have the largest shell of the genus, with a maximum size over 360 mm. But on closer inspection the overall shape looked less sleek, the shell had patches of dark brown periostracum, and remarkably there wasn't any spot on the exterior surface to be found with the glossy nacre that is so typical of Cymbium glans. Also the columellar folds were of a uniform flesh colour, not white like in Cymbium glans. Recently, a new Cymbium species was described from the mouth of the Congo River in southern Congo-Kinshasa and northern Angola: Cymbium coenyei Nolf, 2017. All fifteen type specimens came from the same locality and the largest measured 153 mm. Even though the giant Cymbium from Cameroon is more than twice this length, its morphological features match well with this newly described species. Whether or not this giant shell is indeed Cymbium coenyei is of course still open for debate. Cymbium shell morphology Comparison between Cymbium glans and the giant Cymbium cf coenyei specimen Cymbium coenyei Nolf, 2017 Nolf (2017) describes a solid, slender shell with a fairly straight outer edge, a narrow posterior canal and three columellar folds. The two most distinctive morphological details he mentions are: 1. only the sutural incision of the last whorl (the body whorl) is visible. The sutural incision lies right beneath the spiriform sutural crest and has for the most part been buried under a continuous deposit of callus on the sutural ramp.. 2. the protoconch is covered with a brown callus, alhough this feature is not always so obvious in some specimens, as can be seen in the holotype and paratypes 7 and 14. Cymbium glans (Gmelin, 1791) The protoconch is usually small or even rudimentary, but specimens with a larger protoconch have been observed. Both the protoconch and the sutural ramp are completely covered by callus in Cymbium glans, giving it the appearance of glazed stoneware. This glossy callus layer hides the details and the deeper lying parts of the spiral on top, and usually reduces the visibility of the protoconch in case it never grew large in the first place. The sutural crest is variable both in shape and in height. Sometimes it grows short and in longitudinal direction, in other specimens the sutural crest is longer and fans out considerably. The sutural ramp is horizontal to slighlty tilted upward, the posterior canal deeply concave. The parietal area does not have a callus.layer; the shell lacks a parietal plate. The shape is elongated, the widest point of the aperture at about two fifth of its length, and the strongest curvature of the lip roughly at the same spot, giving it a sleek appearance. The external colour is grey, pinkish or brown and the exterior surface is covered with a silvery nacre layer and sand grain inclusions of varying degree. The colour of the aperture varies from cream to pinkish flesh colour. There are three columellar folds, two smaller ones in the middle with a similar shape, and the third one stretched toward the anterior. The colour of the columellar folds is white to cream, with orange or pink furrows in between. The fasciole has got the same colour and gloss as the rest of the exterior, perhaps the colour is slightly lighter. And it has got a well defined though relatively fine siphonal sculpture. The siphonal canal is wide, in some specimens shallow, in others somewhat deeper. The giant Cymbium cf coenyei specimen from Cameroon The shell shape is rather slender with the aperture at its widest at about one third of its length and the curvature of the lip strongest at about one quarter of its length, which gives it a bulging appearance. The colour of the shell is pinkish brown, with a rust coloured protoconch that stands out sharply against the duller brown background. The top is relatively cylindrical and only slightly curved inward, as a result of a short sutural crest that has grown in longitudinal direction. The sutural ramp is only slightly pointing upward, making the spiral on top resemble a shallow gully. On the last few inches of the sutural ramp, right behind the posterior canal, a pink layer of callus has been deposited with one large sickle-shaped marking. The posterior canal is concave and is relatively narrow, even though its width varied during growth, as can be observed from the inconsistent spiral on top, which is shaped by the sutural crest. The last few centimeters of the concave edge of the posterior canal is covered by a pinkish callus, the same colour as the aperture. The parietal area is very narrow, almost without parietal callus. The aperture is pinkish with brown streaks. There are three strong columellar folds with a brownish flesh colour. The fasciole is sharply defined, whitish, and with a clearly visible siphonal sculpture. The siphonal canal is shallow and wide in this specimen. The exterior surface has got a periostracum, which is patchy on the ventral side and almost absent on the dorsum. Some patches of encrusting bryozoa. The most important differences A number of morphological elements are markedly different between the shells of Cymbium glans and the giant Cymbium cf coenyei specimen. Below a table. Cymbium glans Cymbium cf coenyei Cymbium coenyei exterior silvery nacre with sand lacks nacre, instead a lacks nacre, instead patchy surface inclusions patchy brown periostracum dark brown periostracum usually small, blends in has got a rust colour, deep covered with dark brown protoconch with the surface reddish brown callus sutural has got uniform surface uniform but rough surface, the callus is layered, with ramp texture, even glossy callus from orange to light brown sickle-shaped markings ** columellar white ridges with orange in uniform brownish flesh white, brown or grey folds between colour shell length max. over 360 mm 323 mm largest 153 mm ** This characteristic is not in Nolf's original description. Discussion Marche-Marchad & Rosso (1978) gave an elaborate description of Cymbium glans, in which the protoconch was described as 'a little visible or not visible at all'. There are however examples of Cymbium glans specimens with a larger and clearly visible protoconch, comparable with the protoconch of for example Melo aethiopicus (Linnaeus, 1758). Even though Nolf (2017) presented a number of key characteristics of Cymbium coenyei, some of those cannot be regarded as certain or consistent. The holotype and the fourteen paratypes show that Cymbium coenyei is a species with a high morphological variability, especially regarding overall shape and the sutural elements. Specimens can have a slender outline (paratypes 4, 7 and 13) or instead a broad mango-like shape (paratypes 1, 9 and 10). There is another given key feature of Cymbium coenyei that does not show similarity among the type specimens: the narrow siphonal notch (or siphonal canal) in Cymbium coenyei as opposed to the wide siphonal notch in Cymbium patulum (as shown in Plate XXVII), is not evident in paratypes 1, 4, 9, 12, 13 and 14. The sutural ramp varies in width, even in individual specimens, with the result that the spiral on top often has a whimsical character, as can be seen in paratypes 5, 10 and 14 for example. Also the amount of parietal callus is variable; paratype 5 has got a well defined parietal plate, while the holotype hasn't got much parietal callus at all. Nolf's type material originated from one locality only, and this could possibly result in uniform geographical adaptations and phenotypical similarity. All of the specimens of Cymbium coenyei were found off the mouth of the Congo River, which carries a trail of black mud into the sea for miles. In such a muddy environment it is likely that the aperture of the specimens remains without much pigmentation and that the periostracum becomes almost black. Individual animals living away from river estuaries may well develop a shell with a different colour, which may also differ in size as a result of different environmental conditions - which may or may not be optimal for the species. The morphology of Cymbium coenyei is characterised by variability; not only between individuals but also within the lifespan of one individual. Because of the overall allometry it is hard to identify this species on the basis of separate morphological elements alone. These morphological elements have congruence however, but when identifying the species synthesis seems to be required, perhaps similar to face recognition. The very large specimen from Cameroon is named Cymbium cf coenyei instead of Cymbium cf glans, because morphologically it resembles Cymbium coenyei more than Cymbium glans, even though its size alone would suggest Cymbium glans without any shadow of doubt. Simply because there isn't any species known in the region that grows 32 cm tall besides Cymbium glans. The morphology however seems to be too distinct to call it a gerontic specimen of Cymbium glans with a grown-out shape. The three largest other known species are: 1. Cymbium pepo (Lightfoot, 1786), which can grow to about 30 cm, but its globose shape makes it morphologically very dissimilar. 2. Cymbium senegalense Marche-Marchad, 1978. This species can grow to 30 cm, but only resides in the Senegalese waters.