Gonatocyrtoceras longissimum Dzik, 1984 from Cheiloceras Zone, Famennian in Poland;
1. Adult living chamber in lateral (a) and dorsal (b) views, ZPAL N/224 ; bed J. 6, Jablonna .
2. Adult living chamber in ventral (a ) and lateral (b) views, specimen from the burned collection of the Geological Institute, Warsaw ; supposedly Kadzielnia .
3. Longitudinal section through a phragmocone, ZPAL N/237 ; Jablonna ; x 2.
4. Adult living chamber in lateral (a), dorsal (b), and septal (c) views, specimen from the burned collection of the Geological Institute, Warsaw ; supposedly Kadzielnia .
5. Adult specimen in ventral (a) . lateral (b), dorsal (c), and septal (d) views, ZPAL Nf223, holotype ; bed J . 7, Jablonna.
6. Adult specimen in dorsal (a) and lateral (b) views. ZPAL N/227 ; Kadzielnia .
7. Longitudinal section through a phragrnocone, ZPAL N/301; Kadzielnia ; x 2.

Diagnoza

Long, weakly curved shell with siphuncle situated between the shell center and venter; aperture laterally constricted and the plane of funnel sinus situated normally to the depressed head part of peristome.

Porównanie

G. longissimum widely differs from its congeners in its long shell with considerably laterally constricted aperture. Its phragmocone fragments resemble Lysagoraceras
in external view, but differ in the siphuncle lying away from the venter. G. longissimum differs from its relatives also in the separation of the ventral pair of retractor muscle scars. This is a primitive feature reported thus far from Ordovician (SWEET 1959) and Llandoverian (MIAGKOVA 1967) representatives of the Oncoceratida. However, this could be owing to the considerable length of the living chamber.
Variability. - There is a very wide intrapopulation variability in the collections from Jablonna and Kadzielnia. It consists mostly in the size of the mature shell, the length
of the mature living chamber, and shell curvature. The shape of the aperture obviously is ontogeny-dependent.

Autekologia

Występowanie geograficzne

The species has thus far been recorded only from the Cheiloceras Zone
at Kadzielnia and Jablonna (beds J. 6 to J. 7). The specimens from Jablonna are smaller in average.

Zasięg czasowy

Cheiloceras Zone (beds J. 6 to J. 7).

Materiały muzealne

Literatura

Dzik, J. 1984a. Phylogeny of the Nautiloidea. Palaeontologia Polonica 45, 1-255