Gothograptus diminutus, 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 : 466

Gothograptus diminutus n. sp.

Fig. 23

1999 Gothograptus nassa ( Holm, 1890) , Kozłowska-Dawidziuk, p. 156, fig. 3B.

2016 Gothograptus nassa ( Holm, 1890) , Kozłowska, p. 535, fig. 1b.

Type material. Holotype ZPAL G.29/21, mature specimen with six pairs of thecae ( Fig. 23B, C, E ); paratype ZPAL G.55/34, mature tubarium with six pairs of thecae and appendix ( Fig. 23D ). Bartoszyce IG-1well, depth 1659.9 m, Poland, parvus / nassa Biozone.

Etymology. Latin diminutus— relating to the small size of the finite tubarium.

Diagnosis. Small finite tubarium reaching six or seven pairs of thecae and appendix. Genicular structures of the nassa type of hood are usually developed on medial and distal thecae. It differs from other Gothograptus species in the small hoods and small number of thecae.

Material. Bartoszyce IG-1 core, Poland, parvus / nassa Biozone , depths 1659.9 m; five mature specimens, and about 60 young tubaria or fragments; 1658.8 m, a few specimens.

Description. Tubaria of G. diminutus n. sp. are small; length of mature tubarium with six pairs of thecae and appendix is about 5.0– 5.5 mm. Nema short. Length of appendix is about 0.6 mm. Width of proximal end above the ancora umbrella rim is 0.7 mm. Maximum width of tubarium reaches about 0.9 mm at the level of second and third pairs of thecae. The tubarium slowly tapers distally; below the appendix it is 0.4–0.5 mm wide. Mid-ventral lists are slightly longer in medial thecae, about 0.7 mm. Length of mid-ventral list of th1 1 is 0.35 mm. Mature tubaria have nassa - type hoods developed on medial and distal thecae. The biggest hoods are in distal thecae. Mature tubaria usually have thin lists and poorly developed reticulum ( Fig. 23A, D ). Some membrane of the metasicula is observed ( Fig. 23B, F ). The outer ancora is not observed.

Remarks. Gothograptus diminutus n. sp. is the smallest form among the Gothograptus species. It is distinctive in that its mature tubaria do not have thick lists and dense reticulum, characteristic of mature colonies of all other Gothograptus species. This form is comparable in size to the dwarf monograptid, Pristiograptus parvus . It is noteworthy that both species occur at the same stratigraphical level, in the parvus / nassa Biozone. This material comes only from the Bartoszyce IG-1core of Poland.

Figures

FIGURE 23. Gothograptus diminutus n. sp. Bartoszyce IG-1core, Poland. A. lateral view of tubarium, almost mature, with seven pairs of thecae, 1659.9 m, ZPAL G.55/32. B, C, E. mature tubarium with six pairs of thecae and appendix, holotype, 1659.9 m, ZPAL G.29/21; B. ventro-lateral view; C, fragment of third pair of theca; E. proximal end. D. finite tubarium with six pairs of thecae and appendix, paratype, depth 1659.9 m, ZPAL G.55/34. F. mature tubarium with seven pairs of thecae, ventrolateral view, depth 1658.8 m, ZPAL G.54/8. G. young tubarium with four pairs of thecae, depth 1659.9 m, ZPAL G.55/35.