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Comprehensive Description

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Description

Thysanodonta new genus

 

 

TYPE SPECIES: Thysanodonta aucklandica n.sp.; Recent, New Zealand.

 

ETYMOLOGY. From the Greek Thysanos (fringe, tassel) and odontos (tooth).

 

DIAGNOSIS. Shell trochiform, white, up to 18 mm high, anomphalous, spire high and rather evenly conical. Protoconch sculptured with fine threads in pattern of interconnected hexagons. First 1.5-2.5 teleoconch whorls unicarinate. Subsequent whorls with flat or shallowly convex sides, sculptured with rounded, nodular spiral cords, S3 present. Jaw rectangular, longer than broad, with median longitudinal channel, elements narrowly tapered, narrowing outwards. Radula teeth hair-like, tip of each with long narrow terminal cusp and series of slender, backwardly inclined barbs, shafts with short anteriorly inclined barbs.

 

DESCRIPTION. Shell up to 18 mm high, trochiform, anomphalous, spire tall and rather evenly conical; periphery angulate, rounded in extremely large specimens; base shallowly convex, predominantly white, nacreous through translucent outer shell layer.

 

Protoconch sculptured with tight network of interconnected hexagons, terminal varix strong.

 

Teleoconch of up to 7.3 whorls. First 1.5-2.5 whorls unicarinate (P3), subsequent whorls flat or slightly convex. First 0.25-0.3 whorl delin­eated by growth scar, with strong axial varix, spiral threads, and minute granules. Subsequent whorls sculptured with spiral cords and axial costae, intersections on spire with rounded nod­ules. Axials strong on 1st 2 or 3 whorls, weak­ening and becoming obsolete on next whorl, thereafter represented by rounded nodules on spire spirals. Spiral cords numbering 4-8 on adult penultimate whorl, and 9-14 on base, the latter including P4, summit of which is almost or entirely covered by succeeding whorls. P3 com­mencing almost immediately, other spirals com­mencing on 2nd or 3rd whorl. Spiral interspaces concave, finely granulate. Aperture subcircular or subquadrate. Outer lip thin at rim, thickened within. Inner lip thin, parietal lip a thin glaze.

 

Jaw (T. aucklandica) rectangular, longer than broad, smooth central channel flanked by longi­tudinal series of slender, anteriorly-inclined, tapered elements that decrease in size outwards.

 

Radula (T. aucklandica): Teeth similar, exceedingly slender, hair-like, 1.1-3.4 mm long and 2.4 µm wide, cylindrical in section. Number per cross-row difficult to ascertain but appar­ently 10 or 11. Tip of each tooth with a very long, slender, gently curved, terminal cusp, fol­lowed by sharp, slender, backwardly inclined barbs in a series 1.5-2 times longer than terminal cusp; 2 slender barbs beside and outwardly splaying from main series at distal end of barbed area. Shafts of teeth with a line of minute, widely spaced, sharp, anteriorly-inclined serrations.

 

Animal (T. aucklandica) white. Head dor­soventrally flattened; cephalic tentacles flat­tened, tapered, edges finely papillose; basal eyestalks large; eyes large, black. Snout flat­tened, longer than broad, laterally expanded, flattened in front. Left neck lobe large, semi­circular, right lobe weaker. Sides of foot finely pustulated. No epipodial tentacles detected (contracted?); edge of operculigerous lobe con­voluted and strongly papillose. Operculum chi­tinous, multispiral. Anterior alimentary tract narrow; buccal cavity long and narrow, packed with teeth to mouth opening.”

 

 

(Marshall, 1988: 217)

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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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