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Comprehensive Description

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Description

“Genus Venustatrochus n.g.

 

Type: V. georgianus n.sp.

 

 

This genus is provided for a benthic species from South Georgia, which on external shell features is not dissimilar from normal deep-water thin-shelled Calliostomids. The dentition, however, is different from that of typical Calliostoma, Photinula and the Photinula-like Calliostomids of the Magellan Province that generic separation is essential. Normal Calliostomids exhibit a radula with from four to seven laterals and a central tooth with a simple, more or less rectangular base, which is deeper than it is broad. The inner marginal is massive, long and somewhat crooked at the end, and bears on the underside a small number of prominent comb-like denticles. The central and laterals have long and slender curved cusps which are delicately serrated, and it is difficult to imagine how they can be effectively used without suffering damage.

 

The radula of Venustatrochus resembles that of the Calliostomids in the possession of large inner marginals with comb-like cusps and elaborately serrated, slender, curved cusps on the central and laterals. The discordant features are shown in the central tooth, which has a long, very narrow cusp on a large diamond-shaped base, and in the laterals, which are as the central except for being cut away on the inner side of the base. The most remarkable difference is in the number of laterals (sixteen) which is greater than in any other known Trochoid.

 

Formerly the West Indian Livonia pica, which has nine laterals, was quoted as the Trochoid with the largest known number of these teeth (Fig. H, 17). A curious similarity between the radulae of Venustatrochus and Livonia is that they both have a diamond-shaped base to the central. In Livonia however, the inner marginal is a massive hooked tooth and none of the teeth has the long, slender serrated cusps of the Calliostomids. I do not consider that the resemblances noted between the radulae of Venustatrochus and Livonia indicate close relationship, and certainly the shell features are discordant in almost every particular.”

 

 

(Powell, 1951: 92)

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© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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