Trocholites sp. 1
Creators: name: Aubrechtová, Martina
name: Korn, Dieter
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Tarphyceratida
Trocholitidae
Trocholites

description: Trocholites sp. 1
Fig. 28; Table 19
Material examined
GERMANY • 1 spec.; probably Brandenburg; Ordovician; Neben and Krueger Coll.; illustrated in Fig. 28; MB.C. 32179.
Description
Specimen MB.C.32179 (Fig. 28) is a conch with a maximum diameter of 36 mm; it was sectioned in transverse plane. The conch consists of about 4.5 volutions. During ontogeny between 3.6 and 35.4 mm conch diameter, the relative conch width and coiling rate decrease markedly (CWI from 0.89 to 0.49; WER from 2.60 to 1.74) and the umbilical width increases (UWI changes from 0.21 to 0.41). The whorl profile has convex flanks and a flattened venter, which becomes rounded adaperturally; the dorsal impression (IZR) first increases from 0.17 to 0.37 up to 15 mm conch diameter and thereafter decreases from 0.37 to 0.23 in the subadult and adult stage. The whorl profile generally becomes less depressed during ontogeny (WWI decreases from 2.44 to 1.57), but the decrease is not gradual. The siphuncle appears to be located near the dorsal shell wall in inner whorls and moves to the subdorsal position in later whorls; the RSH is between 0.20–0.16.
Remarks
In several of the specimens of Trocholites, the shell wall is noticeably thickened at the ventral and lateral sides of the conch and particularly the umbilical wall. This is best seen in specimen MB.C.32179, where the shell wall is about 0.5 mm thick at a conch diameter of 35 mm and even up to 0.7 mm thick at the umbilical wall.
The specimen MB.C.32179 is kept in open nomenclature due to insufficient preservation of external morphology and the siphuncle; also, it cannot be reliably inferred, whether the specimen represents an adult or subadult growth stage. However, some comparisons to other specimens of Trocholites are still possible. Both the whorl width and whorl height of the terminal body chamber gradually increase in the specimen of Trocholites sp. 1, as it does in T. glacialis sp. nov. and T. sp. 3. However, in T. sp. 1 the whorl profile shows a flattened venter. The whorl profile is, at dm ~ 35 mm conch diameter, less depressed in the specimen MB.C.32179 of T. sp. 1 when compared to T. glacialis (WWI = 1.57 vs 1.80), but more depressed than in the specimen of T. sp. 3 (WWI = 1.80 vs 1.30).
The specimen MB.C.32179 of Trocholites sp. 1 differs from the specimen MB.C.32168 of T. macrostoma in ontogenetic trajectories between conch diameters of 5 to 25 mm (Fig. 11). In the former specimen, UWI is lower (decrease followed by increase) and CWI higher (increase followed by decrease).
Similar to Trocholites sp. 1 is T. zaryensis sp. nov. but the outer volution of the latter is more discoidal (CWI = 0.57 vs 0.49) and much more depressed (WWI ~ 1.82 vs 1.57); the venter is flattened (vs rounded) all the way up to the aperture. In T. kadakaensis sp. nov., the whorl profile is also much more depressed (WWI ~ 1.82 vs 1.57) than in Trocholites sp. 1.
The holotype of Trocholites ruedemanni is a very similar in conch geometry to the specimen MB.C.32179 (and also the specimen MB.C.32180 of T. sp. 2) but T. ruedemanni has nodes and costae on the umbilical wall of the outer two volutions; also the flattening of the ventral side seen in MB.C.32179 is not present (Flower 1943).
Trocholites sp. 2
Fig. 29; Table 20
Material examined
POLAND • 1 spec.; Międzyzdroje; Darriwilian; illustrated in Fig. 29; MB.C. 32180.
Description
A transverse section was made from specimen MB.C.32180 (Fig. 29), which is a conch with about 29 mm diameter. Three outer whorls are preserved; a part of the conch belongs to the body chamber. During ontogeny between 4.3 and 28.5 mm diameter, the conch decreases in width ratio and coiling rate (CWI from 0.74 to 0.55; WER from 2.52 to 1.66) and increases in umbilical width (UWI changes from 0.18 to 0.47). The whorl profile is rounded from all sides, moderately impressed and increasingly depressed (WWI change from 1.66 to 1.97). The whorl height and width gradually increase with conch growth. The siphuncle is not visible clearly in the section but appears to be marginodorsal or nearly so, and medium in diameter (estimated RSH between 0.15 and 0.20).
Remarks
Specimen MB.C.32180 is left in open nomenclature here because of poor preservation of external characters, as well as the siphuncle. The specimen appears most similar to MB.C.32179 of T. sp. 1 in the ontogenetic trajectories of conch dimensions and ratios (Fig. 11). However, the whorl profile in MB.C.32180 becomes more depressed (instead of less depressed) in growth (WWI generally increases from ~ 1.7 up to ~ 2). Also, the ventral side of the whorls is not flattened in MB.C.32180.
The conch geometry in the specimen MB.C.32180 is also similar in several aspects (mainly WER) to the geometry of the specimen MB.C.32168 (T. macrostoma). However, the ontogenetic trajectories differ between conch diameters of 5 to 25 mm. In that interval in MB.C.32180, the UWI is lower (decreases and then increases) and CWI is higher (increases and then decreases); WWI is similar in late growth stages but lower in earlier growth stages.
Trocholites sp. 3
Fig. 30; Table 21
Material examined
GERMANY • 1 spec.; probably Brandenburg; Ordovician; Neben and Krueger Coll.; illustrated in Fig. 30; MB.C. 32181.
Description
A transverse section was produced from specimen MB.C.32181 (Fig. 30). This is a specimen with 31 mm conch diameter and shows 1.5 volutions preserved. During the last volution, the conch decreases in the whorl width ratio (CWI changes from 0.56 to 0.42) and increases in the umbilical width ratio (UWI changes from 0.34 to 0.42), while the coiling rate remains nearly constant (WER ~1.80). The last volution of the conch shows a decelerated increases in height, while the whorl width increases gradually. The whorl profile shows rounded flanks and venter; the whorl profile is widest in its dorsal half (i.e., not in the middle of the flank). The WWI is between 1.65 and 1.47 but changes in a fluctuating manner; at the greatest conch diameter, the whorl profile is weakly depressed (WWI = 1.30). The depth of the imprint zone is also irregular and decreases from a value of IZR = 0.33 to 0.23. The diameter of the siphuncle is about 0.20 of the apertural height; it has a position close to the dorsal shell wall or is even in contact.
Remarks
The insufficient preservation of the specimen MB.C.32181 prevents its unequivocal taxonomic assignment; the specimen is thus left in open nomenclature.
In Trocholites sp. 3, both whorl width and whorl height of the terminal body chamber gradually increase, which is similar to T. glacialis sp. nov. and T. sp. 1. However, the whorl profile of T. sp. 3 is, at 30 mm conch diameter, much less depressed (WWI ~ 1.30 in T. sp. 3, but ~ 1.80 in both T. sp. 1 and T. glacialis).
Trocholites sp. 4
Fig. 31; Table 22
Material examined
GERMANY – Brandenburg • 1 spec.; Liepe; Lasnamägi or Uhaku Regional Stage, late Darriwilian; Müldner Coll.; illustrated in Fig. 31A; MB.C. 32182.
Description
A transverse section was prepared from specimen MB.C.32182 (Fig. 31), but the conch is re-crystallised internally and therefore, some dimensions had to be estimated. The specimen has a conch diameter of 24 mm; it is thinly discoidal (CWI = 0.40), subevolute (UWI = 0.43) and moderately expanding (WER = 1.82). The whorl profile is weakly depressed (WWI = 1.26) and moderately impressed dorsally (IZR = 0.18). Flanks and venter are broadly convex. The maximum width of the whorl profile is reached in the midflank area. The ornament is poorly preserved and consists of irregularly spaced narrow ribs and lirae, which are straight on the flank and form a ventral sinus. The suture line is straight. The phragmocone chambers are moderately long (RCL = 0.26 at wh = 6.7 mm). Siphuncle can be measured at the largest whorl height, where it has a rather narrow diameter (RSH) of 0.21; it is close to the dorsal side throughout ontogeny.
Remarks
The specimen MB.C.32182 is left in open nomenclature because re-crystallisation prevented accurate measurements of internal conch characters.
In conch geometry, Trocholites sp. 4 is most similar to T. depressus, particularly to specimen MB.C.32161 (Fig. 7). However, the siphuncle does not seem to be in contact with the dorsal shell wall in T. sp. 4 and is much narrower (RSH = 0.21 vs 0.30 in T. depressus).
The specimen of Trocholites sp. 4 is also nearly identical in conch geometry to the two specimens of T. tureki sp. nov. (Fig. 7), but the ornament in the former specimen is much finer and less regularly developed.
description: Published as part of Aubrechtová, Martina & Korn, Dieter, 2025, The coiled Middle Ordovician cephalopod genera Trocholites and Curtoceras (Tarphyceratida) from Baltoscandia and north-central Europe, pp. 1-78 in European Journal of Taxonomy 982 on pages 54-59, DOI: 10.5852/ejt.2025.982.2843, http://zenodo.org/record/15096341