Comprehensive Description

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"Falsilunatia notorcadensis n.sp. (Figs 236, 270)


MATERIAL EXAMINED: Eltanin Stns 1078, 1079, 1082, 1083, 1084.


DISTRIBUTION: Apparently confined to waters surrounding the South Orkneys in 284-604 m.


DESCRIPTION: Shell of medium size, solid, depressed, globose, umbilicate. Height a little greater than diameter. Spire relatively low. Apex worn in all specimens, remaining whorls about four, whorl outline evenly rounded, sutures abutting although periostracum tends to withdraw from sutures slightly in dead shells. Surface covered by moderately thick, chestnut brown periostracum, with broad axial bands paler in colour than remainder, giving an axially striped appearance. Shell surface with irregular, microscopic, rather scratchy spiral striae. In addition there are substantial, broadly rounded, obliquely set, rather irregularly spaced spiral ridges, most marked on last whorl, but obsolete on penultimate, crossing broad axial ribs which coincide with paler bands on periostracum. This combination of broad major spiral and axial elements gives the shell surface a maleated appearance. Aperture ovate, outer lip thin, inner lip spread as a rather solid glaze over parietal area. Columella solid, slightly but freely reflected to cover a small part of the other-wise widely open, deep umbilicus. Axial sculpture somewhat accentuated as it enters umbilicus. Operculum large, horny, paucispiral, brown and relatively fragile. Radula with single cusp on central tooth, and simple unicuspid lateral.


MEASUREMENTS: height 29.0 mm, diameter 27.3 mm (holotype); height 25.6 mm, diameter 25.0 mm (paratype).


HOLOTYPE: from Eltanin Stn 1078, in National Museum of Natural History, Washington (USNM 860105).


PARATYPES: from Eltanin Stn 1082 (one, USNM 860106) in National Museum of Natural History; from Eltanin Stn 1084 (one, MF.56599), in National Museum of New Zealand.


REMARKS: The radula matches that of Globisinum and those of other species assigned below to Bulbus. However, this radula does not differ markedly from that of Falsilunatia, merely lacking the vestigal cusp on the lateral and those on the central. The shell is solid and widely umbilicate, and the animal can be withdrawn completely into the shell. For these reasons it seems best placed in Falsilunatia rather than in Bulbus. The submalleate shell surface, the dark periostracurn and the low spire all point towards Amauropsis, but the radula, at least, shows that it cannot be accommodated in this latter genus. The shape of the shell, the relatively low spire, the widely open umbilicus, the strong, obliquely set spiral sculpture, and striped epidermal colour pattern amply characterise this new species."


(Dell, 1990: 150-151)


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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