Pleurotomaria wiesberghausensis, 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 : 13-16

Pleurotomaria wiesberghausensis n. sp.

( Figs 14–28 )

Type specimens – Holotype: GBA 2018/002/0002/01 ; paratypes: GBA 2018/ 002/0002/02–03 .

Type locality – Hierlatz Alpe (Hallstatt, Austria) .

Type strata – Lower Jurassic Hierlatz Limestone from the Semicostatum Zone ( Lower Sinemurian ) to Jamesoni Zone (Lower Pliensbachian) interval .

Derivation of name – Wiesberghaus is a tourist place, not too far SE from the locality.

Diagnosis – Moderately elevated shell of several (7–8) whorls, forming conoid with blunt apex and gradate outline. Angulation sharp from third to latest whorl; ramp narrow. Outer face as whole steeply sloping abaxially; adapical half barely concave, remaining belt slightly convex. Wide selenizone at midwhorl. Outer face joined to base along rounded angulation. Base flattened and broadly phaneromphalous. Ramp bearing collabral riblets with granules at ridge of angulation initially then riblets and granules together swollen into nodes, extending from suture to selenizone. Fine collabral threads regularly repeated densely on whorl surface, similarly weak lunulae on selenizone. Few spiral threads/cords on whorls: one overlapping ridge of angulation, two threads limiting selenizone and one dividing it. One thread running between selenizone and suture; another thread just overlapped by suture. Nodules on these latter threads from penultimate whorl toward peristome.

Material – Two specimens in (near) full-grown stage and three others represent the early teleoconch; all are damaged (GBA 2018/002/0002/01–05).

Measurements – Holotype (GBA 2018/002/0002/01): height 15 mm, width 14.4 mm, apical angle 76°, pleural angle 71°; paratype (GBA 2018/002/0002/02): height 25mm,width 21mm, apical angle80°; paratype (GBA 2018/002/0002/03): height 7.9 mm, width 8 mm.

Description – The shell consists of 7–8 whorls with moderately elevated spire and a blunt apex. The earliest two whorls have rounded whorl surface; the following whorls are with spiral angulation, causing gradate outline of the shell. The angulation is sharp from the third to the latest whorls. The ramp is narrow and fairly sloping abaxially; it is flat initially but slightly concave from the fifth whorl. The outer face as a whole steeply slopes abaxially; its adapical half is faintly concave, the remaining belt is slightly convex on the latest whorls. A wide selenizone runs at the midwhorl; it is feebly concave in the earliest growth phases but becoming feebly convex on the latest whorls and forms the lower edge of the concave belt of the outer face. The convex belt of the outer face joins to the base through a rounded angulation. The visible shell parts of the holotype and the early shells indicate a base, flattened as a whole with slightly convex wall, and having a rather broad umbilicus.

On the third whorl, the ramp bears dense collabral riblets with granules at the angulation then the riblets and granules together swell into elongate nodes, extending from the suture to the selenizone. They are most prominent at the angulation. On the earliest teleoconch whorls, a narrow network belt of dense collabral and few spiral threads is formed between the selenizone and the suture. From about the fifth whorl, a thinner type of collabral threads substitutes the former one and this ornament type appears also between the selenizone and the upper suture. Similarly weak lunulae ornament also the selenizone. Only few spiral ornamental elements are on the whorls. One thread runs along the ridge of the angulation that becomes a rather wide ribbon for the fifth whorl and lasts through the subsequent shell parts. Two threads limit the earliest selenizone parts, they remain weak also along the next whorls; however, another thread appears within the selenizone in submedian position on about the fourth whorl and it gradually strengthens during the growth. Between the selenizone and the suture, only one spiral thread/cord is visible before the last whorl where a new one, formerly covered by the suture, also appears. These lines bear spirally elongated thickenings from the end of the fifth whorl; the thickenings and their interspaces are arranged to a low undulation of the peripheral shell belt. From the ornament of the base of the holotype, a single thread is visible that seems to be also slightly undulating. On the specimens, representing the early growth stages, sparse spiral threads and dense, delicate growth threads compose the ornament.

Remarks – The early shells are somewhat similar to P. nodulocostulata n. sp. and P. nodulocincta n. sp. in the early growth stages. The distinction is safe from the fifth whorl by the appearance of the new spiral thread on the ramp in case of P. nodulocostulata . In P. nodulocincta the nodules are fewer and somewhat larger already from the 4 th whorl than in P. wiesberghausensis , which possesses almost double number of nodes per whorl. In the latest growth stages further differences appear in the shape and the ornament. The most prominent ones: in P. nodulocostulata , no nodes develop in the peripheral region of the last whorls and the angulation of whorls tends to vanish but remains sharp and nodose in P. wiesberghausensis . The latest whorls of P. nodulocincta change into rounded and the ornament becomes coarse with very fine growth lines while the whorls remain angular in P. wiesberghausensis with more delicate ornament and keep also the regularly repeating, thin growth-threads.

Since the largest but poorly preserved paratype ( Figs 20–22 ) indicates existence of an additional whorl following the last whorl of the holotype some morphological features may be still unknown.

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

Figures

Figs 14–28. Pleurotomaria wiesberghausensis n. sp. – 14–19. Holotype (GBA 2018/002/0002/01). – 14–15. Lateral view better showing the early shell (×3 and ×1). – 16–17. Lateral view for the best outline (×3 and ×1). – 18–19. Apical view (×3 and ×1). – 20–22. Paratype (GBA 2018/002/0002/02), the largest specimen. – 20. Apical view (×1). – 21. Lateral view (×1). – 22. Basal view (×1). – 23–28. Paratype (GBA 2018/002/0002/03) to display the early shell morphology. – 23–24. Lateral view (×4.3 and ×1). – 25–26. Apical view (×4.3 and ×1). – 27. Basal view (×4.3). – 28. Details of the early ornament (×13)