Hierlatzella arcana, Szabó, 2018

Hierlatzella arcana n. sp.

( Figs 57–67 View Figs 51–71 )

Type specimens – Holotype: GBA 2019/009/0033, paratypes (GBA 2019/009/ 0034–38).

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 – Arcanus (Latin) = mysterious.

Diagnosis – Same as for the genus.

Material – Eleven specimens (GBA 2019/009/0033–43), all of them without the protoconch and the earliest teleoconch whorls.

Measurements – Holotype (GBA 2019/009/0033), D = 3.8 mm, paratype (GBA 2019/009/0034),D= 3.8 mm, paratype (GBA 2019/009/0035), D= 3.9 mm, paratype (GBA 2019/009/0036), D = 3.7 mm, paratype (GBA 2019/009/0037), D = 3.8 mm, paratype (GBA 2019/009/0038), D = 4.1 mm.

Description – Small, pupiform, thin-walled shells of low turriculate spire. Teleoconch whorls are initially low and flat with flush suture then slightly convex whorls and somewhat more impressed suture develop. Last whorl extends downward. Base is subglobose with convex wall; its transition to the last whorl is rounded-angular. No specimen has been found with undamaged peristome and earliest whorls. The aperture has depressed ovate outline, formed by a very short but complex columellar-umbilical lip, which is poorly preserved, thin outer lip and the parietal shell wall with probable discontinuity of the peristome. The shell interior contains a relatively thick columella with a spirally built, narrow umbilicus inside. No ornament has been found; the growth lines are very thin and slightly prosocline on the whorls and somewhat more on the base.

Remarks – From Lower Jurassic strata, similarly sized and shaped gastropods have been published by GEMMELLARO M. (1911) as Chemnitzia galatensis (Late Pliensbachian) and as Proconulus ? cf. galatensis (Late? Sinemurian) by SZABÓ (1983, 2009). From these, Gemmellaro’s species is different in having more acute spire and circular peristome but the second form is rather near in shape to Hierlatzella arcana n. sp. In the latter case, early shell riblets and spiral lineation on the base mean significant difference from the Hierlatz Alpe species. Their relation to Hierlatzella arcana n. sp. needs still further studies.

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