Karsaconulus robustus, Szabó, 2018

Szabó, János, 2018, Gastropods of the Lower Jurassic Hierlatz Limestone Formation, part 4. New eucycloidean, trochoidean, neritimorph, and caenogastropod taxa in the fauna of the Hierlatz Alpe (Hallstatt, Austria), Fragmenta Palaeontologica Hungarica 35, pp. 61-84 : 73-74

Karsaconulus robustus n. sp.

( Figs 26–36 )

Type specimens – Holotype: GBA 2019/009/0011, paratypes: GBA 2019/ 009/0012–16.

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 – Referring to the thick wall, heavy columella, and the reinforced peristome.

Diagnosis – Same as for the genus.

Material – Twelve specimens (GBA 2019/009/0011–22), which have been stored under the name “ Trochus avernus ” in Stoliczka’s “background” material so actually they belong to the syntypes of Proconulus avernus (Stoliczka, 1861) .

Measurements – Paratype (GBA 2019/009/0015), H = 8.6 mm, paratype (GBA 2019/009/0013), W = 5.9 mm, (GBA 2019/009/0012), W = 6.8 mm, holotype (GBA 2019/009/0011), W = 7.2 mm, paratype (GBA 2019/009/0014), W = 4.3 mm, paratype (GBA 2019/009/0016), W = 4.8 mm.

Description – All available shells are small, their height rarely exceeds ten mm. They have biconoidal outline with a moderately high and blunt spiral, and a low basal conoid. Full-grown shells consist of about six arched whorls that are strongly convex initially but changing to almost flat subsequently. The protoconch is depressed, almost planispiral. The deeply impressed suture of the early shell progressively alters into almost flush on the following shell parts. Periphery is rounded angular; shallow concavities develop along its both sides during the latest growth phases. The base is low, anomphalous and has slightly convex wall. Formation of a reinforced, complex peristome means the latest growth phase of the shell. The columellar lip is robust and has a thick, wide, periaxial plate as a basis that is surrounded by narrow but marked furrow. Inner lip is thick and has a wide, uneven, mainly concave outer face between the sutural part of the outer lip and the foot of columella; both its basal and apertural edges are sharp. The foot of columella forms an extended, ovate, and slightly concave pad, obliquely crossing the axis. The aperture is orbicular. Observable elements of the outer lip bear sharp outer rim and, in the latest growth stage, the last whorl and the outer lip region slightly extend abaxially.

Ornament is observable from the second whorl as marked spiral threads along at least one whorl, or slightly more then only obscure spiral lines/striae of different width are found on the next whorls and the base. The growth lines are prosocline and feebly prosocyrt on the whorls and opisthocyrt on the base.

Remarks – On the genus characters, most similarly shaped species are easily distinguishable. In the collection, this species has been stored as “ Trochus avernus ”; however, the figured specimen of this species, selected as lectotype by SZABÓ (2009), has Proconulus type peristome. All other specimens belong to Karsaconulus n. gen. In the Hierlatz Alpe fauna, Trochus kneri Stoliczka, 1861 , Proconulus? kneri in SZABÓ 2009, is a rather similarly shaped species but its peristome is also different though it has also a peristome reinforcement.

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

Figures

Figs 20–50. Species of Trochoidea. – Figs 20–25. Callotrochus? avernoides n. sp. – 20–22. Holotype (HNHM, M 59.157), apertural, dorsal, and basal views, ×2. – 23–25. Paratype (HNHM, M 57.3617), apertural, dorsal, and basal views, ×2. – Figs 26–36. Karsaconulus robustus n. gen. n sp. – 26–27. Holotype (GBA 2019/009/0011), apertural and dorsal views, ×3. – 28. More enlarged, slightly oblique view of peristome of the holotype, ×5. – 29–31. Paratype (GBA 2019/009/0012), apertural, dorsal, and basal views, ×3. – 32–33. Paratype (GBA 2019/009/0013), dorsal and apical views, ×3. – 34. Paratype (GBA 2019/009/0013), details of ornament of the early shell, ×13. – 35– 36. Paratype (GBA 2019/009/0014). – 35. Apical view, ×3. – 36. Detailed apical view, ×15. – Figs 37–50. Csigabaga nillae n. gen. n. sp. – 37–40. Paratype (GBA 2019/009/0024). – 37–39. Apertural, dorsal, and basal views, ×3. – 40. Growth line arrangements of the latest base, ×6. – 41–42. Holotype (GBA 2019/009/0023), apertural and lateral views, ×3. – 43. Magnification of the less damaged peristome from among the available specimens, holotype, ×6. – 44–46. Paratype (GBA 2019/009/0025), a not fully grown specimen that shows well the columellar fold without the final peristome modifications. – 44–45. Apertural and dorsal views, ×3. – 46. Aperture, ×6. – 47–48. Paratype (GBA 2019/009/0026), basal views showing the place of the inner fold as shallow depression in normal and oblique position, ×3. – 49–50. Paratype (GBA 2019/009/0027), a damaged shell that exposes the traces of the inner basal fold that developed during the latest growth phase, in slightly oblique and in normal views, ×3