Hedbergella trocoidea

Taxonomy

Original description: Test medium in size, low trochospiral, consisting of about 2 whorls, nearly flat to slightly concave on spiral side, broadly rounded, peripheral outline distinctly lobulate; chambers inflated, subglobular to radially rather elongate, about 7-8 in final whorl, increasing gradually in size as added; sutures distinct, depressed, nearly radial on both sides; wall calcareous, perforate, radial in structure, surface smooth; aperture a low interiomarginal, extraumbilical-umbilical arch bordered above with or without slight lip.

Interessante è notare che spesso l'avvolgimento tende a farsi nettamente trocoide, sì che la conchiglia diviene alquanto convessa, la camera finale viene così ad adagiarsi sulla faccia ombelicale e l'apertura sì estende sull'ombelico in un posizione nettamente asimmetrica (tav. IV, fig. 2-3). Forme analoghe si trovanogià descritte dal Berthelin (1880 p. 69, tav. IV, fig. 11) col nome di Placenta nitida (Reuss). Franke (1925) interpreta piuttosto tale forma come un sinonimo dell'Anomalina lenticula, ma a giudicare dalla stessa figura di Reuss ciò sembra escludersi, poichè questa è più piccola a bordo un po' depresso, giri interni nonvisibili. A giudicare dal nostro materiale sembra più evidente sussistere una relazione tra la forma di Berthelin e l'Anomalina lorneiana (d'Orbigny), forme che nei nostri sedimenti, sottolineano, non sono in alcun modo separabili, poichè troppi passaggi intermedi le uniscono.
Pertanto si può qui parlare di due gruppi di variazioni:
a) varietà quasi planispiralc: typica;
b) varietà nettamente convesa: trocoidea n. var.

[p. 134]:  L'Anomalina lorneiana tipica si distingue, come è evidente, per l'avvolgimento planispirale, pei giri interni più profondi che quelli esterni, sicchè poco visibili. Nelle fig. 2 e 3 (Tav. IV) si sono rappresentati due esemplari della varietà a spirale trocoide. L'individuo della fig. 2 è ancora poco trocoide e un po' involuto superiormente; quello della fig. 3 è per contro tipicamente evoluto. la forma convessa è ben accentuata sì che l'ultima camera si adagia un po' dal lato ombelicale. Da tale lato ambo gli individui sono completamente involuti, le camere della spira esterna si allungano irregolarmente fino al centro. in cui è solo visibile una piccola infossatura. L'Anomalina roberti Gandolfi mostra evidente. quale carattere differenziatore dalla precedente, un largo ombelico centrale; le camere appaiono per conseguenza più bassee larghe.

Entries in the Catalog of original descriptions: Anomalina lorneiana trocoidea

Emended description:

Most likely ancestor: Hedbergella praetrocoidea - at confidence level 4 (out of 5). Data source: .

Geological Range:
Last occurrence (top): at top of P. rohri zone (99% up, 113.3Ma, in Aptian stage). Data source: [copied from Chronos database]
First occurrence (base): within G. ferreolensis zone (118.24-118.56Ma, base in Aptian stage). Data source: [copied from Chronos database]

Plot of range and occurrence data:

• Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
• Triangles indicate an event for which a precise placement has been suggested
• Histogram - Neptune occurrence data from DSDP and ODP proceedings. Pale shading <50 samples in time bin. Interpret with caution & read these notes
• Taxon plotted: Hedbergella trocoidea, synonyms included - Hedbergella trocoidea;
• See also space-time plot :: Samples map :: Parent: Hedbergella

Hedbergella trocoidea compiled by the pforams@mikrotax project team viewed: 11-10-2024 Taxon Search: Advanced Search Short stable page link: https://mikrotax.org/pforams/index.php?id=110269 Go to Archive.is to create a permanent copy of this page - citation notes

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