Danoceras piersalense ( Teichert, 1930 ), 2025

Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, European Journal of Taxonomy 978, pp. 1-169 : 62-65

Danoceras piersalense ( Teichert, 1930) comb. nov.

Figs 16C–D, F, 24D, F–H, 25C, 26

Dowlingoceras (?) piersalense Teichert, 1930: 284 , pl. 6 figs 17–18.

Dowlingoceras (?) piersalense – Strand 1934: 79. ― Miller & Youngquist 1947: 415. ― Balashov 1953a: 208. ― Frye 1987: 95–96.

Emended diagnosis

Danoceras with compressed oval conch-cross section (CHI = 1.2–1.3); mature body chamber with maximum conch height near its base with height of ca 40–45 mm and height to length ratio of ca 0.8– 0.9; conch surface with distinct constriction near peristome and amphora-like apertural opening.

Material examined

ESTONIA • 1 spec.; Vormsi Island , Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 840-93 • 16 specs; Vormsi Island , Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 426-988 , GIT 840-261 , GIT 840-270 , GIT 840-258 a, GIT 840-272 , GIT 878-263 to GIT 878-268 , GIT 878-270 to GIT 878-272 , GIT 878-276 , GIT 878-279 • 1 spec.; same locality as for preceding; TUG 1745-48 • 2 specs; Pirgu River outcrops; Adila Formation, Pirgu Regional Stage; TUG 1745-296 , TUG

1745-302 • 1 spec.; Vohilaid Island , Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-267 .

Type locality and horizon

Piirsalu, Lääne County, in western Estonia; Moe Formation, Pirgu Regional Stage.

Description

None of the specimens assigned to this species is complete, all of them preserve parts of the mature or near mature body chamber and parts of the phragmocone. Specimen GIT 840-271 is a fragment of a mature specimen preserving the most important characters of this species. At the base of the body chamber, the conch height is 46 mm, the width cannot be is estimated as ca 36 mm. A length of 35 mm of the body chamber is preserved, where is has a convex outline and decreases to a conch height of 43 mm at its adoral end. The conch cross section is preserved near the adoral end of the phragmocone; it has a height of 42 mm and a width of ca 31 mm (CHI = 1.35) and an oval shape with a narrower margin at the ventral side. In a length of 39 mm, the phragmocone diameter increases from 31 mm to 41 mm (angle of expansion = 16°). The sutures form a shallow lateral sinus on the dorsal side. At a conch height of 40 mm, they are 6 mm apart (RCL = 0.1). On the surface of the internal mold of the phragmocone, faint longitudinal, ca 1 mm wide striae are visible. The siphuncular segments are subtrapezoidal (Fig. 16F). They have their greatest height near the adapical surface of the septa where they are broadly adnate. At a conch height of 37 mm, the septal distance is 4.2 mm, the greates height of the siphuncle 3.8 mm, and the septal foramen ca 2 mm. The septal necks are suborthochoanitic.

Amongst those specimens with complete mature body chamber preserved, their size, relative lengths, and cross section is slightly variable: in GIT 878-263 the conch height at the body chamber base is

44 mm, 38 mm at the peristome. The length of the body chamber is 44 mm (relative body chamber length = 1) and ca 10 mm from the peristome an inconspicuous constriction occurs ( Fig. 25C ). In TUG 1745-48, the conch height at the body chamber base is 44 mm, 37 mm at the peristome. The length of the body chamber is 30 mm (relative body chamber length = 0.68), and ca 10 mm from the peristome an inconspicuous constriction is present.

The mean relative body chamber length of all measured specimen is 0.79 (n= 18). The mean CHI at the base of the body chamber is 1.3 (n = 18) and the mean conch height at the base of the body chamber is 43 mm (n = 21, max. = 47 mm, min. = 40 mm). The frequency distribution of the mature conch sizes is bimodal: of the 21 specimens with mature body chamber preserved six specimens have a conch height of 40 mm at its body chamber base and four specimens have a conch height of 45 mm ( Fig. 26A ).

The conch cross section is oval, generally narrower on the ventral side, where it is almost angular in some specimens (e.g., TUG 1745-302, GIT 878-264; Fig. 24G ). In specimen TUG 1745-302 the complete body chamber has a length of ca 35 mm, decreases in dorsoventral diameter from the base to the peristome and until ca 20 mm, where a shallow, inconspicuous constriction is present, beyond which, the body chamber diameter increases to ca 33 mm.

The sutures form wide, shallow lateral lobes, almost perpendicular to the growth axis, and a relatively deep saddle on the dorsum. The septa are spaced with a mean RCL of 0.12 (n = 56, max. = 0.13, min. = 0.09). In some specimens, narrow longitudinal furrows are visible on the surface of the internal mold of the phragmocone (e.g., TUG 1745-302, Fig. 24H ). The conch surface is poorly preserved in all specimens and was apparently smooth on the mature body chamber and adjacent parts of the phragmocone.

The characters of the siphuncle are well-preserved in TUG 80-510 (Fig. 16C); at a conch height of 28 mm the septal foramen is circular with a diameter of ca 2.4 mm (RSH = 0.09). The septal necks are very short suborthochoanitic, and the connecting rings are expanded, forming subtrapezoidal segments with slightly convex outline in longitudinal view. The maximum diameter of the siphuncle is more than 3 mm. Near the adapical surface of the septum, the connecting ring is widest, forming a wide adnate area.

The siphuncle is also preserved in GIT 1745-296 at a position where the conch height is 34 mm and septa are 3.8 mm apart (RCL = 0.11). There, the septal foramen is 1.9 mm wide and 2.4 mm high (RSH = 0.07). The septal necks, which are poorly preserved, appear to be suborthochoanitic to cyrtochoanitic

(Fig. 16D). The connecting ring forms subtrapezoidal siphuncular segments, which are widest and have a wide adnation area on the adapical surface of the septa (ca 3.8 mm).

Remarks

Teichert’s original diagnosis is emended here based upon the description and figures of Teichert (1930) and additional information from the specimens described here regarding the CHI, and the location and shape of the siphuncle. Most of the Estonian specimens are slightly deformed. The mean CHI therefore slightly overestimates the compression of the conch cross section. The type specimen, described by Teichert (1930) has a conch height at the base of the body chamber of 47 mm, and a conch width of 35 mm, and hence is larger than most of the specimens described herein, but falls within their range of variation. A bimodal frequency distribution of the mature conch size occurs in the material ( Fig. 26A ; supplementary data 4), but this does not allow for an unambiguous distinction of two species, because all morphological features measured form a continuum of variation.

Danoceras piersalense is identical in its mature size, rate of compression, and angle of phragmocone expansion to D. scandinavicum Strand, 1934 . The latter species has been distinguished from D. piersalense by its more convex adoral part of the phragmocone, which is also more sharply “marked out from the upper part of the conch” ( Strand 1934: 84). These subtle differences are difficult to detect in the often fragmentary material from Estonia, and little is known about the variability of this character among species assigned to D. scandinavicum and D. piersalense . It is therefore highly likely, that D. scandinavicum represents a subjective junior synonym of D. piersalense or that both species are present in the Estonian material but remain undetected therein. Additional, and better-preserved material is needed to solve the problem. The species is assigned to Danoceras , herein, because of the Danoceras - like shape of siphuncle.

Comparison

This is a relatively large species of Danoceras , which can be distinguished from other late Katian species of the genus mainly by its size (conch height at the base of the mature body chamber 40–45 mm). The mature body chamber height of Danoceras breve Strand, 1934 (42 mm) is within the range of the specimens assigned to D. piersalense , herein, but differs in having a phragmocone with a higher angle of expansion (25°).

Dowlingoceras kallholnense Frye, 1987 and Danoceras scandinavicum Strand, 1934 have a mature body chamber of similar conch height at its base (40 mm, 39–42 mm, respectively) but their conch cross section is less compressed (CHI = 1.1–1.2), and the latter additionally is sharply curved on its ventral side. The mature body chamber height of Danoceras broeggeri Strand, 1934 is 56 mm.

Figures

Fig. 25. Diestoceratids from the Pirgu Regional Stage, Estonia. A–B. Dowlingoceras tornense sp. nov., paratype GIT 840-273, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. A. Lateral view, prosiphuncular side left. B. View of the prosiphuncular side. C. Danoceras piersalense (Teichert, 1930) comb. nov., specimen GIT 878-263, from Hosholm shore (tower), Vormsi Island. Scale bar = 10 mm, same scale in all figures.

Fig. 26. Diagrams of the variation mature conch size in Danoceras piersalense (Teichert, 1930) comb. nov. A. Histogram of the frequency of conch heights at the base of the mature body chamber (note the bimodal distribution). B. Conch height and conch width at the base of the body chamber of mature specimens.

Fig. 24. Danoceras Troedsson, 1926 from the Vormsi–Pirgu regional stages, Estonia. A. Danoceras oviforme sp. nov., holotype GIT 878-108, from Moe trench, Vormsi Regional Stage, lateral view. B. Danoceras breve Strand, 1934, holotype GIT 426-988, from Haapsalu holm, Haapsalu, Pirgu Regional Stage, lateral view. C. Danoceras oviforme sp. nov., specimen GIT 80-510, from Piirsalu quarry, Pirgu Regional Stage, lateral view prosiphuncular side toward right. D. Danoceras piersalense (Teichert, 1930) comb. nov., specimen GIT 840-271, from Hosholm shore (tower), Vormsi Island, lateral view. E. Danoceras vohilaidense sp. nov., holotype GIT 878-273, from Vohilaid shore (E), Vohilaid Island, Pirgu Regional Stage, lateral view, prosiphuncular side left.F–H. Danoceras piersalense specimen GIT 840-93, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. F. Lateral view. G. Adapical view, prosiphuncular side to the right. H. Specimen TUG 1745-302, from Pirgu River outcrop, Pirgu Regional Stage, lateral view. Scale bar = 10 mm, same scale in all figures.