Porkunioceras tuba, Kröger, 2007
|
publication ID |
https://doi.org/ 10.5281/zenodo.13741383 |
|
persistent identifier |
https://treatment.plazi.org/id/039187AC-7F3E-6004-FF20-FD7DE5D6FE6B |
|
treatment provided by |
Felipe |
|
scientific name |
Porkunioceras tuba |
| status |
sp. nov. |
Porkunioceras tuba sp. nov.
Figs. 6B View Fig , 7F View Fig .
Derivation of the name: From Latin tuba , tube, referring to the breviconic shell.
Holotype: TUG 1227/24.
Type locality: Porkuni, north Estonia.
Type horizon: Siuge Member, Porkuni Regional Stage, Late Ordovician.
Material.—One complete specimen displaying juvenile, adolescent and mature growth stages, TUG 1227/24, one apex with two chambers, TUG 1227/ 26 in collection of TUG.
Diagnosis.—Same as for the genus, by monotypy.
Description.— Holotype TUG 1227/24 ( Fig. 7F View Fig ), is nearly complete conch of adult specimen. Mature growth stage is indicated by shape of body chamber that is slightly bulged at position somewhat adoral of peristome. Peristome is straight. Total length of specimen is 13 mm, maximum dorso−ventral diameter 7.2 mm, maximum lateral diameter 4.8 mm, body chamber length 4.5 mm. Shell surface is ornamented with straight transverse, raised lirae, eight occur per one millimetre. Last septum has dorso−ventral diameter of 4.3 mm, lateral diameter 3.9 mm. Second septum is 0.8 mm from tip at cross section diameter 2.1 mm. Distance between initial and second septum is 0.4 mm. For measurements of all thirteen chambers of specimen, see Table 1 View Table1 . Apex is acute, shell at apex is not preserved. Siphuncle is marginal at convex side of slightly cyrtoconic growth axis, with diameter 0.2 mm at cross section diameter 2.1 mm.
Specimen TUG 1227/26 ( Fig. 6B View Fig ) is fragment of two apical−most chambers of shell and apex. Tip of apex is acute, like “jelly bag cap”, smooth, with elevation of approximately 0.3 mm. Transverse striation starts at base of acute tip. Second septum occurs at cross section diameter of 2.2 mm measured in dorsoventral direction and 1.6 mm measured in lateral direction.
Remarks.—The fragment of the apex can easily be assigned to Porkunioceras tuba because the holotype is a nearly complete specimen that only lacks a part of the most apical chambers. In the holotype, a part of the apex is preserved. The apex fragment TUG 1227/26 exactly fits to the fragmented apex of the holotype.
Stratigraphic and geographic range.—Chert of the Siuge Member, Porkuni Regional Stage, Late Ordovician from Porkuni, north Estonia.
Gen. et sp. indet A.
Fig. 4G View Fig .
Material.—Three fragments of apices (TUG 1227/34, 35, 36) in the collection of TUG from Chert in the Siuge Member, Porkuni Regional Stage, Late Ordovician, Porkuni, north Estonia.
Description.—Fragment TUG 1227/34 ( Fig. 4G View Fig ) preserves seven apical chambers and complete body chamber of juvenile specimen. Shell is smooth. Total length is 10 mm, maximum dorsoventral diameter 6.5 mm, length of phragmocone 4.5 mm with maximum dorsoventral diameter of four millimetres. Distance between two youngest septa is 0.48 mm. Depth of curvature of septa is one millimetre. Siphuncle is at convex side of shell, close to margin (0.26 mm from margin at youngest septum), tubular with septal perforation at youngest septum with diameter 0.24 mm. Septal necks are achoanitic. Initial septum occurs at distance of 0.16 mm from tip. Initial septal perforation is 0.3 mm wide with achoanitic septal neck. Caecum with diameter 0.34 mm touches shell wall 0.36 mm adapically from initial septum. Septal distance of entire chambers of fragment see Table 1 View Table1 .
Remarks.—The fragments of consideration provide not enough information for a proper species assignation. However, the shape and position of the siphuncle, and the shape of the siphuncular necks allow an assignment to the Graciloceratidae .
Gen. et sp. indet. B.
Fig. 4F View Fig .
Material.—One complete specimen, TUG 1227/25, displaying embryonic and juvenile growth stages, in the collection of TUG from Chert in the Siuge Member, Porkuni Regional Stage, Late Ordovician, Porkuni, north Estonia.
Description.—Fragment represents apical part of nearly complete juvenile specimen with length of six millimetres. Shell is slightly cyrtocone, smooth, with compressed cross section, maximum lateral diameter is 1.8 mm, maximum dorsal−ventral diameter 2.5 mm. Post−apical angle of expansion (measured from 3–9 septum) is 8.41. Diameter is 0.7 mm at position 4.75 mm from apex and 0.15 mm at position one millimetre from apex. Shell thickness at apex is 20 ̊m, at position 4.75 mm from apex 40 ̊m. Thickness of ninth septum approximately six micrometres. Apex is blunt, cap−shaped. Septal curvature is very shallow. For information on septal spacing, see Table 1 View Table1 . Diameter of septal perforation at first septum is 0.12 mm, at ninth septum is 0.18 mm (0.07 of cross section diameter). Septal necks are very short suborthochoanitic with length of 60 ̊m at second septum. Position of siphuncle is between centre and conch margin at convex side of conch curvature. Siphuncular tube is not preserved.
Remarks.—The specimen in consideration can be assigned to the Graciloceratidae because it displays a narrow, eccentric siphuncle and very short septal necks and a breviconic shell. However a specific and generic determination is not possible at the basis of the single juvenile specimen.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.