Strandoceras orvikui, Kröger, 2007
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publication ID |
https://doi.org/ 10.5281/zenodo.13741383 |
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persistent identifier |
https://treatment.plazi.org/id/039187AC-7F3F-6007-FFEA-F936E619FA97 |
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treatment provided by |
Felipe |
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scientific name |
Strandoceras orvikui |
| status |
sp. nov. |
Strandoceras orvikui sp. nov.
Figs. 7A, B View Fig , 10 View Fig .
Derivation of the name: In honour of the Estonian geologist Karl Orviku (1903–1981).
Holotype: TUG 1227/27.
Type locality: Porkuni, north Estonia.
Type horizon: Porkuni Regional Stage, Late Ordovician.
Material.— Five specimens displaying embryonic, juvenile and adolescent growth stages in the collection of TUG .
Diagnosis.—Smooth Strandoceras with very high dorsoventral angle of expansion of 20–30 °. Conch is strongly compressed; lateral diameter is approximately 0.7 of dorsoventral diameter. Similar as in other species of Strandoceras narrow longitudinal ridge occurs at concave side of conch growth axis. Septal spacing is very narrow, 0.12 of dorsoventral diameter. Siphuncular tube is approximately 0.2 of dorsoventral diameter. Apex is smooth, blunt, not constricted from juvenile conch. Second septum occurs at cross section diameter of approximately 0.24 mm.
Description.— Holotype TUG 1227/27 ( Fig. 7A View Fig ) is fragment of juvenile specimen with nearly complete body chamber. Entire length of specimen is 14 mm, maximum dorsoventral diameter 12 mm, maximum lateral diameter 9 mm, minimum dorsoventral diameter 6 mm, minimum lateral diameter 4 mm. Shell is smooth with faint irregular growth lines. Conch is cyrtocone. Approximately 15 longitudinal furrows occur at surface of steinkern representing internal longitudinal ridges at shell. Peristome has shallow hyponomic sinus and shallow saddle at flanks (with 1.4 mm elevation). Complete body chamber length is 6 mm. Last septum occurs at dorsoventral diameter 9.6 mm, and lateral diameter 6.5 mm. Distance between last septum and preceding septum is 0.5 mm. Siphuncle is marginal at concave side of conch with diameter of approximately 1 mm at 6 mm dorso−lateral diameter. Sutures form sharp saddle at ventral side and lobe at flanks. Curvature of last chamber is 1.2 mm deep.
Specimen TUG 1227/28 ( Fig. 7B View Fig ) is fragment of most apical 18 mm of juvenile conch with maximum dorso−ventral diameter 11.3 mm, maximum lateral diameter 7 mm. Septal distance at maximum diameter is 1.3 mm. Shell at apex has faint irregularly spaced growth lines. Internal mould of shell has several longitudinal ridges representing impressions of longitudinal furrows at inner shell surface.
Specimen TUG 1227/30 ( Fig. 10 View Fig ) is a fragment of most apical 14 chambers of phragmocone. Fragment has length of 4.6 mm, maximum dorso−ventral diameter 5.5 mm, distance from initial septum to apex is 0.04 mm, distance from initial septum to second septum is 0.03 mm, there, dorsoventral diameter measures 0.24 mm. For information about septal distances of entire specimen see Table 1 View Table1 . Septal perforation at position of maximum dorsoventral diameter of fragment is 0.6 mm. Diameter of siphuncular tube between youngest preserved chambers is 0.9 mm.
Specimen TUG 1227/29 is fragment of juvenile specimen with eight chambers and incomplete body chamber. Length of fragment is 6 mm, maximum dorsoventral diameter 5.3 mm, thickness of shell wall is 0.08 mm, thickness of septa 0.02 mm. Septal spacing is 0.28–0.44 mm, see Table 1 View Table1 . Dorsoventral diameter at youngest septum is 3.1 mm, there septal perforation measures 0.4 mm and maximum diameter of siphuncular tube is 0.6 mm. Septal necks are achoanitic. Siphuncle is inflated between chambers. Connecting ring is thick.
Occurrences.—Chert and dolomitised limestone of the Siuge Member, Porkuni Regional Stage, Late Ordovician from Porkuni, north Estonia.
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