Granulizona mandli, Szabó, 2017

Szabó, János, 2017, Gastropods of the Lower Jurassic Hierlatz Limestone Formation, part 3. New pleurotomarioideans from the fauna of Hierlatz Alpe (Hallstatt, Austria), Fragmenta Palaeontologica Hungarica 34, pp. 9-48 : 44-46

Granulizona mandli n. sp.

( Figs 140–145 )

Type specimen – Holotype: GBA 2018/002/0015.

Type locality – Hierlatz Alpe (Hallstatt, Austria) .

Type strata – Hierlatz Limestone within the Lower Sinemurian to lowermost Pliensbachian (Lower Jurassic) interval .

Derivation of name – This species is dedicated to Gerhard Mandl, Austrian geologist (GBA).

Diagnosis – Same as for Granulizona n. gen., see above.

Material – A single, rather poorly preserved specimen that shows yet sufficient details to taxonomical treatment; the protoconch and the latest, near-peristome parts are unknown.

Measurements – Height: 33.5 mm, width: 31.5 mm.

Description – A moderately turriculate, trochiform shell of about 12–13 rather low whorls represents this species. The protoconch and about one of the earliest teleoconch whorls are very poorly preserved, the next eight visible whorls have feebly acute (coeloconoidal) outline but the last three whorls turn into slightly cyrtoconoidal. The suture is impressed along the full visible length of the shell. The earliest two visible whorls are flattened and have a shallow depression along the selenizone that seems flat here. In the next growth phases, the whorls gradually change into fully flat first then increasingly convex. Concomitantly the selenizone becomes convex from the third visible whorl, and rises higher than the arch of the whorls, like a weak carina. From the initial midwhorl position, the selenizone gradually shifts quite near to the lower suture during the growth. Its width is about 10% of the distance between the neighbouring two sutures. Below a narrow outer face, the shell turns through a slightly rounded angulation into the base that is rather flattened cone as a whole; its wall is feebly convex. Remnants of at least a half additional but broken whorl indicate presence of a rather wide phaneromphalus. No part of the peristome has been preserved but the growth-lines indicate a strongly prosocline outer lip with a slight sinus in an extremely abapical position, near the rim of the base.

Short, regularly repeating riblets ornament the belt adapically from the selenizone on the first five visible teleoconch whorls. Synchronously with the riblets, nodules develop along the abapical suture and tiny granules appear also on the selenizone; their periodicity is similar to those of the riblets and nodules but they are formed in different phase. The riblets and nodules gradually vanish on the fifth visible whorl while the granules of the selenizone remain present also on the next two whorls, devoid of riblets, but their density gradually increases then they fuse into a continuous keel, persisting along the following whorls. Variably strong growth-lines, which irregularly become strengthened as threads sometimes, mean the transverse ornament on the remaining parts of the shell. They are strongly prosocline and prosocyrt adapically from the selenizone and feebly opisthocline-prosocyrt in the narrow belt abapically. The growth-lines of the selenizone are invisible, probably they are extremely fine and erosion and/or the recrystallisation has smoothed them. Subregularly spaced spiral lines and threads are present on the whole outer surface of the shell excepting the selenizone and perhaps some belts of the base.

Remarks – The shape and ornament of the latest whorls resemble to those of Laevitomaria Conti et Szabó, 1987 species but the early whorls with sparse riblets between the upper suture and the selenizone, and granulae on the selenizone distinguish these two genera. The same early whorls in Granulizona n. gen. remind Pleurotomaria Defrance, 1826 but the lack of an angulation from the whorls and mainly the presence of the granulae on the selenizone are distinctive characters. Since the position of the selenizone is near the abapical suture on the last whorls, a distinction from Pyrgotrochus Fischer, 1885 is also necessary. Differently from Pyrgotrochus , these whorls are clearly convex and the outline of the shell is trochiform in Granulizona but the shell shape is coeloconoidal or conoidal in Pyrgotrochus with mostly flat or concave whorls and, in addition, a peripheral swollen belt somehow develops.

Distribution – Within Sinemurian to lowermost Pliensbachian (Lower Jurassic) part of the Hierlatz Limestone Formation in Hierlatz Alpe, Hallstatt, Austria.

Figures

Figs 140–145. Granulizona mandli n. sp., holotype (GBA 2018/002/0015). – 140–141. Lateral view with the best preserved spots of the ornament (×1 and ×2.8).– 142–143.Lateral views, which clearly show the trochiform outline (×1). – 144. Basal view (×1). – 145. Details of the ornament and the alteration of the sculpture between the early and latest whorls (×6)