Semigothograptus meganassa ( Rickards & Palmer, 2002 )

Kozłowska, Anna, 2016, A new generic name, Semigothograptus, for Gothograptus? meganassa Rickards & Palmer, 2002, from the Silurian post- lundgreni Biozone recovery phase, and comparative morphology of retiolitids from the lowermost upper Homerian (upper Wenlock), Zootaxa 4208 (6), pp. 534-546 : 536-538

Semigothograptus meganassa ( Rickards & Palmer, 2002)

( Figs 1 D, 2B, 3, 4B, 7A–D)

2001 Gothograptus nassa Holm, 1890 (wide form)—Kozłowska-Dawidziuk, Lenz & Štorch, pp. 151–152, fig. 4: 11–12. 2002 Gothograptus ? meganassa Rickards & Palmer , pp. 228–231, text-fig. 4.

Diagnosis. Genicular hoods of nassa type, reticulum dense in mature colonies.

Material. Four fragments of isolated tubaria with up to six pairs of thecae, from laminated marls, Bartoszyce IG-1 drill core, depth 1649.2 m and 1649.0 m, geographical coordinates 54˚14’ N, 20˚57’S, Poland, eastern part of Baltica, East European Platform. Based on flattened graptolites Tomczyk (1974) assigned the interval 1636.5– 1650.0 m to the dubius / nassa Biozone , upper Homerian, Wenlock. The material comes from the uppermost part of the dubius / nassa Biozone. The studied material was isolated from the rock though slow dissolution in 10–30% hydrochloric acid (HCl), for cleaning specimens with sediment attached 10% hydrofluoric acid (HF) was used. Specimens are stored in glycerine in plastic containers, and on SEM stubs in the Institute of Paleobiology, Polish Academy of Sciences in Warsaw.

Description. Length of immature tubarium with proximal end, ZPAL G.54/1, consisting of four pairs of thecae is 5.4 mm ( Fig. 1 D). The distance from the ancora umbrella rim to the lip of th1 1 is 1 mm. Length of lateral apertural rods increases gradually from 0.94 mm in the first theca up to 1.1 mm in the fourth. Width of tubarium measured between thecal lip and lateral apertural rod also increases distally. Width of tubarium on the th1 1 level is 0.7 mm, on th2 1 is 0.8 mm, on th3 1 is 1.1 mm, and th4 1 level is 1.2 mm.

Specimen ZPAL G.54/2, representing possibly a more distal part of tubarium, is parallel-sided, about 1 mm wide.

The proximal ventral orifices are of triangular shape ( Fig. 1 D, 4B). The proximal lateral orifices are located centrally, between looping meshes of the ancora umbrella. The looping meshes are developed on both sides of tubarium forming a wavy shape of the ancora umbrella rim ( Figs 2 , 4 B). They are smaller on the th1 1 side of tubarium ( Fig. 2 B). Within the looping meshes are some thin additional lists ( Fig. 2 B).

Inside specimen ZPAL G. 54/2 there is a free list, which may represent a fragment of the free virgella or nema ( Fig. 3 B). Lateral apertural rods (pleural lists of Rickards & Palmer 2002) are long, and distinctly convex towards the longitudinal axis of the lateral walls. Clathrial lists of the lateral walls of tubarium are relatively thin, oblique, going from lateral apertural rod to lateral apertural rod of tubarium ( Fig. 4 B).

Thecal apertures are almost rectangular. Genicular hoods are of nassa type. On the immature specimen the hoods are present on the first thecae, becoming larger in the medial part of tubarium and absent in the two distal growing thecae ( Figs 1 D, 4B). In some thecae there are some narrow open spaces between bandages, possibly due to taphonomic changes ( Fig. 7 A–D). Some irregular bandages are secreted on the outer surface of the upper part of the hoods ( Fig. 7 A, D).

The largest specimen, of six pairs of thecae, is preserved in two fragments with no proximal end ( Fig. 3 ). The specimen possibly represents the medial part of the tubarium.

The reticulum of the tubarium is composed of thin lists, dense in the proximal and medial part of the growing colony, becoming weaker distally, and not developed in the most distal immature part of the tubarium.

Figures

FIGURE 1. Tubaria of A – C. Gothograptus nassa Holm, 1890 and D. Semigothograptus meganassa (Rickards & Palmer, 2002) from dubius / nassa Biozone, Bartoszyce IG- 1 drill core, Poland. A. Gothograptus nassa, obverse view of mature tubarium with destroyed distal end, long morphotype, ZPAL G. 54 / 5, 1655.8 m, B. latero-ventral view of mature tubarium with appendix, short morphotype, ZPAL G. 54 / 8, 1658.8 m, C. long appendix, ZPAL G. 54 / 10, 1656.8 m. D. Semigothograptus meganassa, obverse view, ZPAL G. 54 / 1, 1649.2 m, uppermost part of dubius / nassa Biozone.

FIGURE 2. Proximal ends showing ancora umbrella looping meshes of A. Gothograptus nassa Holm, 1890 early growth stage, ZPAL G. 54 / 7, Bartoszyce IG- 1 drill core, depth 1656.8 m; B. Semigothograptus meganassa (Rickards & Palmer, 2002), ZPAL G. 54 / 1, Bartoszyce IG- 1 drill core, depth 1649.2 m.

FIGURE 3. Light photos of Semigothograptus meganassa (Rickards & Palmer, 2002), specimen broken into two parts, ZPAL G. 54 / 2, Bartoszyce IG- 1 drill core, depth 1649.2 m; A. with sediment before cleaning in HF; B – C. two sides of lower part of the fragment after cleaning in HF. Abbreviation: lat. ap. rod—lateral apertural rod.

FIGURE 4. Comparison of the main structures of tubaria used in this study. A. Papiliograptus papilio Lenz & Kozłowska- Dawidziuk, 2002, Šiupyliai- 69 borehole, Lithuania; B. Semigothograptus meganassa (Rickards & Palmer, 2002), ZPAL G. 54 / 1, Bartoszyce IG- 1 drill core, depth 1649.2 m; C-D. Gothograptus nassa Holm, 1890, C. young colony, reverse side, ZPAL G. 54 / 4, Bartoszyce IG- 1 drill core, depth 1656.8 m, D. mature colony with broken distal end, obverse side, ZPAL G. 54 / 5, Bartoszyce IG- 1 drill core, depth, 1655.8 m. Scale 1 mm for all pictures. Abbreviations: anc. — ancora, sl. — sleeve, umbr. — umbrella.

FIGURE 7. SEM pictures of nassa type genicular hoods of Gothograptus nassa Holm, 1890 and Semigothograptus meganassa (Rickards & Palmer, 2002). A – D. Semigothograptus meganassa, ZPAL G. 54 / 1, 1649.2 m, Bartoszyce IG- 1 drill core, Poland, uppermost part of dubius / nassa Biozone, A. hood of th 2 2 with marked surface bandages (arrow). B. enlargement showing pustules on parallel bandages (arrow), C. hood of th 1 2 with marked space between bandages (arrow), D. hood of th 3 2, surface bandages (arrow). E – H. Gothograptus nassa, Bartoszyce IG- 1, 1655.8 m, dubius / nassa Biozone, E. whole hood of th 3 2, irregular bandages arrowed, specimen ZPAL G. 54 / 3. F – G. enlargement of hood, ZPAL G. 54 / 9, F. showing pustules on parallel bandages (arrows), G. presenting edges of subjacent bandages (arrows). H. fragment of hood of mature specimen with thick layer of irregular bandages with distinctive pustules and parallel bandages (arrow), ZPAL G. 54 / 6.