Gothograptus velo, 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 : 462-466

Gothograptus velo n. sp.

Fig. 22

1990. Gothograptus (Gothograptus) sp. A. Kozłowska-Dawidziuk, pp. 202–203, pl. 24: 2; fig. 6A–E.

Type material. Mature tubarium, holotype ZPAL G.XIII/35, Zawada 1 core, depth 1533.3–1540 m, Poland, upper part of lundgreni Biozone.

Material. One finite tubarium with nine pairs of thecae.

Diagnosis. Proximal thecae with no genicular structures, successive medial and distal thecae have genicular veils. The veils are built of thin reticular lists; there are no thicker lists at the end of the veil as in G. obtectus . Reticulum below thecal lip undergoes reduction in distal thecae.

Description. The mature tubarium has nine pairs of thecae. The distal end is slightly damaged, together with the appendix ( Fig. 22 ). The tubarium length is 10.1 mm, together with the extending nema. The width of the tubarium at the level of the first pair of thecae is 0.8 mm. The widest part of the tubarium is 1.2 mm at the level of the fifth thecal pair. The tubarium tapers distally to a width of 0.6 mm at the level of the ninth pair of thecae. The sicula length is 1.5 mm; the prosicula apex is connected to the lateral wall of the tubarium at the level of the lip of th1 2. The thecal lips are thick whereas the genicular lists are thinner in distal thecae but well developed and easy to distinguish ( Fig. 22B ).

The two first pairs of thecae do not have genicular structures. The first well-developed veil is on the fifth pair of thecae. Some reticular lists of the veil of th6 1 are connected to the geniculum of th5 1, and to the reticulum of the th5 1 veil ( Figs 9C , 22B ). The reticulum of the ventral thecal wall is well-developed up to the fifth pair of thecae, but distally, below the long veils, it become poorly developed, eventually disappearing under the veils of the last thecal pairs. The genicular and mid-ventral lists below the veils exhibit a similar decrease in thickness, becoming as thin as some lists of the veil ( Figs 9C , 22B ).

The outer ancora is well-developed in the mature tubarium, and built of thick reticulum ( Fig. 22D ). Some membrane of the metasicular wall is connected to the virgella ( Fig. 22C ). Proximal internal structures typical of the genus Gothograptus are present, but they are difficult to distinguish in the flattened material to hand. The nema is distinctively thicker than other lists of the tubarium, and the thickest part starts at the level of th5 1.

Remarks. G. velo n. sp. differs from Gothograptus obtectus in the development of veils. The veils of G. velo are built of a delicate reticulum with no thick transverse lists as in G. obtectus . Some of the veils are connected to the veil of the previous theca, forming an external layer above the thecal orifices and thecae ( Fig. 9C ).

Figures

FIGURE 9. Morphology of two types of veil with coloured lists of tubaria. A–B Gothograptus obtectus Kozłowska- Dawidziuk, 1990, Lithuania, Šiupyliai-69 core, depth 1012.0 m, lundgreni Biozone; A. fragment of tubarium with two veils, ventro-lateral view; B. coloured drawing of ventral wall. C. Gothograptus velo n. sp. distal fragment of tubarium, ventro-lateral view, Zawada 1 core, depth 1533.3–1540.0 m, upper part of lundgreni Biozone, Poland, ZPAL G.XIII/25. Drawings DEB.

FIGURE 22. A–F. mature tubarium of Gothograptus velo n. sp., holotype, Zawada 1 core, depth 1533.3–1540.0 m, upper part of lundgreni Biozone, Poland, ZPAL G.XIII/35, specimen with nine pairs of thecae. A. lateral-ventral view of specimen; B. enlargement of distal part of tubarium; C. enlargement of proximal end; D. view of outer ancora from outside; E–F. enlargements of th7 1. Abbreviations: anc.—ancora, lat. ap.—lateral apertural, v.—ventral, th—theca.