Gothograptus nassa ( Holm, 1890 )

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 : 447-451

Gothograptus nassa ( Holm, 1890)

Figs 10–12

1890 Retiolites nassa Holm , p. 25, pl. 2, figs 12–14.

1891 Gothograptus nassa Holm, Frech , pp. 670–671, fig. 223, 5–6.

?1900 Retiolites nassa Holm ( Gothograptus, Frech ), Wood, p. 486, fig. 27.

1908 Retiolites (Gothograptus) nassa (Holm) , Ellis & Wood, pp. 343–344, fig. 225, pl. 34, figs 15a,d.

?1952 Gothograptus nassa ( Holm, 1890) , Bouček & Münch, pp. 11–15, fig. 2, a–i.

1952 Gothograptus intermedius Bouček & Münch , pp. 15–16, fig. 3 e–f.

1956 Gothograptus nassa ( Holm, 1890) , Tomczyk, pp. 42–44, fig. 8.

1979 Gothograptus nassa ( Holm, 1890) , Obut & Zaslavskaya, pp. 30–33, figs 1–4.

1999 Gothograptus nassa ( Holm, 1890) , Kozłowska-Dawidziuk, fig. 3.

Material. The specimens of Gothograptus nassa studied come from Lithuania, Poland and Gotland. Material from Lithuania comes from the Šiupyliai-69 core, nassa Biozone (above parvus ), at depths from 998.4 m to 997.0 m yielding 130 specimens and the Kybartai-14 core, depth 1087.8 m, a few specimens. The material from Poland, Bartoszyce IG-1 well, comes from the interval 1661.0 m to 1643.9 m, representing the parvus / nassa , dubius / nassa , and lower part of the praedeubeli biozones (see range chart in Porębska et al. 2006, fig. 2). The material is rich, containing about 2,000 specimens, representing different stages of growth of colonies. The Swedish material comes from Gotland, Blåhäll, locality 813–832, Blåhäll 1 ( Spjeldnaes 1984), Dapps and Tegelbruk.

Description. The tubaria represent mostly fragments of colonies at different stages of growth. The longest tubarium of 18 pairs of thecae is 2.8 cm long. It is an immature colony as it has not developed an appendix, and the distal part is not densely reticulated ( Fig. 10A ).

The tubarium of Gothograptus nassa is almost parallel-sided. It widens from a proximal width of about 1.0 mm below the orifice of the first theca and reaches its maximum width (~ 1.2–1.4 mm) in the middle part of the tubarium, following which it tapers distally.

The sicula length is about 1.4–1.5 mm. The mature tubaria have thick reticulum surrounding proximal lateral and ventral orifices ( Fig. 4 H ). There is a strong metasicular rim and reticulum around the sicula, which may represent the walls of th1 1 and th1 2. In some specimens a part of the membrane of the sicula is preserved. An outer ancora is rarely developed in mature specimens ( Figs 4F , 12D ).

Genicular hoods of nassa type are developed successively during astogeny. The new, rich material illustrates hood development through the successive stages of the astogeny of colonies. Hoods are well developed in all thecae in mature colonies ( Fig. 12 ).

The appearance of the first genicular hood in young G. nassa colonies may be on different thecae ( Fig. 10 ). Young tubaria of up to six pairs of thecae usually do not have hoods developed. The first genicular hood may appear on the proximal or medial part of the tubarium. Thus some tubaria do not have hoods on several pairs of thecae but tubaria with e.g. eight pairs of thecae may already have well-developed hoods on six proximal thecae. The longest sub-mature tubarium with eighteen pairs of thecae represents the intermediate stage of colony growth. It has larger hoods in the middle part of the tubarium ( Fig. 12A, C, I ). The size of hoods increases during astogeny; in mature colonies the larger hoods, especially in the distal part of the tubarium, cover the thecal orifices for some distance below. The largest hoods are usually located in the medial part of colonies ( Fig. 12A, I ). The distal thecae are shorter and their genicular hoods are irregular. The rich material of different stages of astogenetic growth of G. nassa colonies also shows a marked variability in the shape of hoods from almost rectangular to ovate ( Fig. 12A, C ).

In mature colonies the clathrial and reticular lists have similar thicknesses. The proximal orifices, both ventral and lateral in old colonies, are partly overgrown by some reticular lists. The nema is thicker at the distal end, and extends about 0.5–0.7 mm out of the tubarium. The appendix is well developed, about 1.5 mm long.

Remarks. The thickened sicular rim and sicular reticulum, as well as an outer ancora umbrella, were first described by Bates & Kirk (1978, p. 431, pls. 2, 6–7). Obut and Zaslavskaya (1979) described the astogeny of Gothograptus nassa based on material from the deep 1-R core of from the Kaliningrad District of the Peribaltic Syncline, from the nassa Biozone. Based on the specimens illustrated by Bouček & Münch (1952, figs. 3e, f) at various stages of growth, co-occurring with G. nassa , the authors established that Gothograptus intermedius Bouček & Münch, 1952 represents young stages of growth of G. nassa . The observations presented herein, based on material from the cores of Lithuania and Poland, support this judgement.

Figures

FIGURE 4. Proximal ends of young and mature tubaria of (A–B) Gothograptus auriculatus n. sp., Bartoszyce IG-1 core, depth 1645.2 m, praedeubeli Biozone, light blue colour indicates ancora umbrella rim; A. immature tubarium with the first three thecae, obverse view, ZPAL G.55/6. B. mature tubarium, obverse view, with wide lists above proximal lateral orifice (dark blue), ZPAL G.55/23. C, D, E, G, H. Gothograptus nassa (Holm, 1890), Mulde Marl, Blåhäll, Gotland, Sweden Locality 813- 832, Blåhäll 1 (Spjeldnaes 1984); C. inside view of proximal end with sicula rim, ZPAL G.55/8. D. outside view of ancora, stereopair, ZPAL G.55/9. E, outside view of ancora, stereopair, ZPAL G.55/10. G. stereopair of proximal end, ventral view, ZPAL G.55/11; H. lateral view with colored reticulated wall of metasicula, ZPAL G.55/12. F. Gothograptus kozlowskii Kozłowska-Dawidziuk, 1990; erratic boulder, Jarosławiec 147, Poland, lundgreni Biozone, outside view of proximal end, with outer ancora, ZPAL G.XIII/43. Abbreviations: anc.—ancora umbrella, lat.—lateral, m-v—mid-ventral list, prox.—proximal, orif.—orifice, th—theca, umb.—umbrella.

FIGURE 10. Immature tubaria of Gothograptus nassa (Holm, 1890) from Bartoszyce IG-1, depth 1655.8 m, dubius/nassa Biozone, Poland. A–B. tubarium with 18 pairs of thecae, ZPAL G.28/1, A ventro-lateral view; B. enlargement of hood of th15 1. C–E. ventral view of tubarium with 10 pairs of thecae, ZPAL G.55/13; C. whole tubarium; D. enlargement of hood of th8 1; E. enlargement of hood of th10 2. F. tubarium with nine pairs of thecae, ZPAL G.28/2. G. tubarium with 10 pairs of thecae, ZPAL G.55/14. H. tubarium with 13 pairs of thecae, ZPAL G.55/15.

FIGURE 11. Tubaria of Gothograptus nassa (Holm, 1890) from Lithuania. A–B, E–F. Specimen with five pairs of thecae, VU RET-8, Kybartai-14 core, depth 1087.8 m, nassa Biozone; A. ventro-lateral view; B. view of distal end; E, enlargement of cross-section of nema; F, distal view of end of tubarium. C–D, G. tubarium with four pairs of thecae, ventral view, VU RET-9, Šiupyliai-69 core, depth 998.0 m, nassa Biozone; C. enlargement of th1 2 orifice; D. oblique view of th1 2 orifice; G. whole specimen.

FIGURE 12. Mature specimens of Gothograptus nassa (Holm, 1890) from Bartoszyce IG-1 core, depth, Poland. A. distal fragment with eight pairs of thecae and appendix, G.55/16. B. fragment of distal end, ZPAL G.55/17. C–E. tubarium with 12 pairs of thecae, ZPAL G.55/18; C. ventro-lateral view of specimen; D. enlargement of orifice of th2 1; E. enlargement showing thickness of hood. F. medial part of specimen with five pairs of thecae, ZPAL G.55/19. G–H. proximal fragment of fragment of specimen with five pairs of thecae, ZPAL G.55/20; G. ventro-lateral view; H. enlargement of th4 1. I–J. distal fragment of tubarium with 10 pairs of thecae and appendix, ZPAL G.55/21; I. whole specimen; J. enlargement of thecal hood.