Orthoceratida, Kuhn, 1940

Aubrechtová, Martina, Turek, Vojtěch & Zicha, Ondřej, 2020, Early ontogenetic growth stages of Middle Ordovician orthoceratoid cephalopods from Bohemia, Acta Palaeontologica Polonica 65 (3), pp. 575-588 : 584

publication ID

https://doi.org/ 10.4202/app.00721.2020

persistent identifier

https://treatment.plazi.org/id/0391878B-7A7A-FF84-A353-FA32F3E6EE08

treatment provided by

Felipe

scientific name

Orthoceratida
status

 

Orthoceratida View in CoL indet. sp. 4

Fig. 6B View Fig .

Material. — Two specimens (MWB S 06827, 06828), counterparts of juvenile shell parts from the locality Volduchy ; Šárka Formation , lower and middle Darriwilian Stage, Middle Ordovician; Czech Republic .

Description. —MWB S 06827 is a counterpart of the embryonic shell including the initial chamber. The length of the specimen is 3.2 mm. The initial chamber (= first phragmocone chamber) is bean-shaped in median section, 1.8 mm in diameter. The phragmocone is constricted at a distance of 1.3 mm from the tip of the initial chamber and at 1.5 mm of shell diameter. This constriction is assumed to correspond to the position of the first phragmocone septum; the shape ratio of the initial chamber is then 0.72 and constriction ratio 0.83. The phragmocone is circular in cross-section. Longitudinal, faintly sinuous shell ornamentation; it disappears at the adoral part of the specimen where it is replaced by slightly oblique transverse sculpture.

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