Gothograptus auriculatus, Kozłowska & Bates & Zalasiewicz & Radzevičius, 2019

Kozłowska, Anna, Bates, Denis, Zalasiewicz, Jan & Radzevičius, Sigitas, 2019, Evolutionary significance of the retiolitine Gothograptus (Graptolithina) with four new species from the Silurian of the East European Platform (Baltica), Poland and Lithuania, Zootaxa 4568 (3), pp. 435-469 : 451-454

Gothograptus auriculatus n. sp.

Figs 13–14

2006 Gothograptus nassa, Calner, Kozłowska, Masiak & Schmitz , p. 80, fig. 1E.

Type material. Holotype ZPAL G.55/23, mature specimen with six pairs of thecae and distal end broken off ( Fig. 13 B ); paratype ZPAL G.55/24, distal end of mature tubarium with five pairs of thecae and appendix ( Fig. 13 C, F ). Bartoszyce IG-1well, depth 1645.2 m, Poland, lower part of praedeubeli Biozone.

Etymology. Latin auriculatus —relating to the earlobe shape of the genicular structures.

Diagnosis. Tubarium with genicular structures formed by the nassa type of hood, and paired vertical auriclelike structures bordering both sides of the thecal orifices. Auricle structures are characteristic only of Gothograptus auriculatus n. sp. In mature colonies the auricles bend towards the mid-ventral list below the thecal lip and nassa hood.

Remarks. G. auriculatus n. sp. differs from G. nassa in having two lateral auricles, as additional elements located on the lateral sides of the thecal orifices and below the lips. Young colonies of the new species have nassa hoods; the auricles appear later in astogeny.

Material. The material studied comes from Poland, Lithuania and Germany. The most abundant material comes from the Bartoszyce IG- well, ranges from 1649.0 to 1645.2 m, praedeubeli Biozone , yielding about 1300, mostly young, specimens. Two fragments of G. auriculatus come from Lithuania, Pilviskiai-141 core, depth 842.2 m, nassa / praedeubeli Biozone.

Description. Tubaria slightly widening up to th1 2, then parallel-sided and gently tapering distally, ended by an appendix. Most of the specimens are represented by fragments of tubaria up to the 11th thecal pair. Tubarium width at the level of the first thecal pair is about 1.5 mm, and in the middle part of the tubarium 1.2 mm. The longest fragment of tubarium, comprising 11 pairs of thecae, is 10 mm long.

The lists of the young stages of colony are very thin, about 15 µm across, while the lists of the mature tubarium are about five times thicker, at 75 µm. The thickening of lists starts from the proximal end. The looping meshes of the ancora umbrella are overgrown by a reticulum in the mature colonies. The ancora prongs below the lateral proximal orifices and the lists surrounding the proximal lateral orifices are extremely wide in mature specimens ( Fig. 14 C–F).The reticular lists also become very wide in mature colonies, making the reticulum meshes very small. In the most mature specimens the reticulum lists reach similar thicknesses to those of the main lists of the tubaria ( Fig. 13D ).

Based on well-preserved specimens representing the young tubaria, the sicula length is estimated at 1.4 mm, the length of the prosicula at 400 µm ( Fig. 2 ). The nema starts at the level of the th1 2 geniculum and is connected to the obverse lateral wall of the tubarium.

The typical genicular structures are well developed in mature specimens. During astogeny the auricles, typical of this species, are first developed in more distal thecae ( Fig. 13 A–C). The longest hoods in mature specimens are about 370 µm long, and extend below the lips. As a consequence the thecal orifices are not visible. The hoods of astogenetically old tubaria may be elongated in the centre of their lower parts ( Fig. 13E ). The distal thecae are shorter and their genicular structures are usually irregular and shorter horizontally ( Fig. 13E ).

In mature specimens, the nema widens distally to about 67 µm across at the most distal end of the tubarium and in the appendix ( Figs 3 , 13C ). A nematularium was not identified.

Remarks. Gothograptus auriculatus n. sp. has been described from the praedeubeli Biozone of Sweden, and published as G. nassa ( Calner et al. 2006, fig. 1E). This taxon, also found in erratic boulders from Germany, has been illustrated and identified by Jaeger as Gothograptus nassa late form ( Maletz 2010, figs 1, 2). The specimens, stored in the Museum für Naturkunde, Berlin, come from a fauna containing the type material of Colonograptus praedeubeli .

Figures

FIGURE 2. Immature tubaria of Gothograptus auriculatus n. sp. from the Bartoszyce IG-1 core, depth 1645.6 m, praedeubeli Biozone, Poland. A. tubarium with four pairs of thecae, ZPAL G.55/1. B. tubarium with two pairs of thecae, ZPAL G.55/2. C– E. tubarium with first pair of thecae, ZPAL G.55/3; C. ventro-lateral view, D. enlargement of distal part of virga with trace of prosicular apex, E. enlargement of distal end showing virga and fragment of virgella. Abbreviation: pros.—prosicular.

FIGURE 3. Gothograptus auriculatus n. sp., fragments of distal parts of tubaria showing a thick nema, Bartoszyce IG-1, depth 1647.2 m, praedeubeli Biozone, Poland. A–B, distal end of tubarium with broken appendix, ZPAL G.55/4, A, fragment with beginning of appendix, B, enlargement of last thecal region showing thick nema. C, lateral view of fragment of medial part of tubarium, ZPAL G.55/5.

FIGURE 13. Mature tubaria of Gothograptus auriculatus n. sp., Bartoszyce IG-1 core, depth 1645.2 m, praedeubeli Biozone, Poland. A. lateral-ventral tubarium aspect with six pairs of thecae, with the distal end broken off, ZPAL G.55/22. B. obverse side of tubarium with proximal end, holotype, ZPAL G.55/23. C, F. reverse views of distal fragments with six pairs of thecae and appendix, paratype ZPAL G.55/24; C. whole specimen; F. enlargement of distal part showing thick lists and auricle. D. part of tubarium with proximal end, reverse view, ZPAL G.55/25. E. ventral view of distal part of tubarium with beginning of appendix, ZPAL G.55/26.

FIGURE 14. Gothograptus auriculatus n. sp., proximal ends of tubaria, Bartoszyce IG-1 core, depth 1645.2 m, praedeubeli Biozone, Poland. A. immature tubarium with the first three thecae, reverse view, ZPAL G.55/27. B. ventro-lateral side of tubarium, ZPAL G.55/28. C–E. reverse views of mature tubaria with very wide lists surrounding proximal lateral orifice and prongs; C. ZPAL G.55/23; D. lateral view, ZPAL G.55/29; F.