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Description

"Laevilitorina (Corneolitorina) labioflecta n.sp. (Figs 187, 188)

 

MATERIAL EXAMINED: Eltanin Stns 410, 1870, 1871, 1907.

 

DISTRIBUTION: Known only from off the South Shetland Islands and the Ross Sea in 220-891 m.

 

DESCRIPTION: Shell large for the group, turbinate-ovate, height less than diameter, openly umbilicate. Shell almost entirely lacking in lime, with a thick epidermis generally pale brown in colour, but black in two specimens from the Ross Sea. Whorls 3 ¾ including a protoconch Of 1 ½ smooth, whitish whorls. Spire whorls considerably flattened, last whorl greatly inflated. Suture impressed. Epidermal surface smooth except for growth lines and faint subsutural spiral threads. Aperture comparatively large, subcircular, attached to last whorl over only a short section of parietal area. Outer lip with a shallow, wide sinus in the middle. Columellar lip widely expanded, quite free. Umbilicus widely open, deep. Operculum circular, spiral, with central nucleus.

 

Radula with an elongate central tooth, bearing a strong, blunt, central cusp, and three minor pointed cusps on each side.

 

DIMENSIONS: Height 6.9 mm, diameter 7.4 mm (holotype); Eltanin Stn 410, paratypes 5.9 x 6.2 mm, 5.3 x 6.1 mm; Eltanin Stn 1871, 6.0 x 7.2 mm.

 

HOLOTYPE: from Eltanin Stn 410, in National Museum of Natural History (USNM 860099).

 

PARATYPES: from same locality, in National Museum of National History (3, USNM 860100) and in National Museum of New Zealand (2, MF.56598).

 

REMARKS: There is some variation in shell proportions, but the Ross Sea specimens do not seem to be separable from the type series from off the South Shetlands.

 

This thoroughly unexpected and decidedly anomalous member of the Littorinidae, collected from two widely divergent areas of Antarctica and living in comparatively deep water, is difficult to place generically. In shape it is closest to Laevilacunaria Powell, but it lacks the very broad chisel-shaped cusp on the central tooth of the radula and the circum-umbilical ridge on the shell that are characteristic of Laevilacunaria. It contrasts with Pellilitorina, which also has a short spire, in lacking hair-like processes on the epidermis and in its very different radula.

 

Like Corneolitorina it has very little lime in the shell but only a thick, leathery epidermis. The central tooth of the radula has a much smaller central cusp than is present in the radula of Corneolitorina coriacea Melvill and Standen, 1907, although in C. heardensis Dell, 1964 it is closer to the central cusp.

 

Although Powell (1951) gave drawings of the radulae of most of the southern genera of the Littorinidae, the true structure of the teeth can only be demonstrated with the scanning electron microscope. Arnaud and Bandel (1976) have presented SEM studies of six of the 19 species recorded, representing three of the six named genera and subgenera. While this represents a significant advance in our knowledge of the group, critical evaluation of the radulae of all species is necessary before the supraspecific classification of the group is possible.

 

The broad emargination of the outer lip in L. labioflecta is quite anomalous for the group. It corresponds with the depression where the columellar lip impinges on the last whorl and would be consistent with the animal in life being attached to a cylindrical support of some kind such as a brittle star arm or a polychaete worm tube. No such association seems to have been recorded for any southern littorinid. The habitat is considerably deeper than for any other antarctic or subantarctic member of the family, and there seems little doubt that the specimens were living at the depths where the collections were made. When all the southern littorinids are monographed it may be necessary to erect a new genus for L. labioflecta. In the meantime it is placed in subgenus Corneolitorina."

 

(Dell, 1990: 110-111)

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Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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