Neogothograptus reticulatus, Kozłowska & Lenz & Melchin, 2009

Kozłowska, Anna, Lenz, Alfred & Melchin, Michael, 2009, Evolution of the retiolitid Neogothograptus (Graptolithina) and its new species from the upper Wenlock of Poland, Baltica, Acta Palaeontologica Polonica 54 (3), pp. 423-434 : 428-431

Neogothograptus reticulatus sp. nov.

Figs. 3 , 5–7 .

1995? Gothograptus sp. Rickards, Packham, Wright, and Williamson,

1995: 41, figs. 18K, L, 20J.

Type material: Holotype: ZPAL G. 41/1, proximal end with five first thecae ( Fig. 5 ), Prągowiec ravine; paratypes: ZPAL G. 41/2 to ZPAL G. 41/6, Baltic boulder 59, Jarosławiec; ZPAL G. 41/7 and ZPAL G. 41/8, Bartoszyce borehole, depth 1630.7 m.

Type locality: Prągowiec ravine, Bardo, Holy Cross Mountains, Poland .

Type horizon: Colonograptus praedeubeli Biozone, Homerian, Wenlock, Silurian.

Diagnosis.—Dense reticulum of thin lists on ancora sleeve and thecal walls, outer ancora, reticulation well developed. Reticulated hoods fully developed on geniculum. Appendix well developed. Lateral and ventral orifices covered with fine meshworks.

Material.—The material comes from three localities in Poland: Bartoszyce borehole 1630.7 m, stub 210, SEM 011410, five specimens; Baltic erratic boulder 59, Jarosławiec, Ludlow, 25 coarse fragments, and many small fragments; nodules 7, 10, and 11 from Prągowiec ravine, Bardo, Holy Cross Mts., one larger specimen and 20 small fragments. All forms come from Colonograptus praedeubeli Biozone. Associated fauna: C. praedeubeli , Pristiograptus dubius .

Description.—Outer ancora well developed in mature rhabdosomes ( Figs. 5C, D , 7D ). Holotype outer ancora is partly broken on th 11 side ( Fig. 5A 2). On the second thecal row of the holotype rhabdosome, a well−developed edge is formed by the outer ancora ( Fig. 5A–C ). The lateral and ventral proximal orifices are completely obscured by thin reticular lists ( Fig. 5D ). No complete rhabdosomes are known. The longest specimen, which appears to be almost complete (missing the appendix and the ancora), is 5 mm long and consists of five pairs of thecae ( Fig. 7 ). Width across first theca 0.8–1.0 mm (extrapolated to 1.3–1.55 mm when flattened) and the maximum width at the second or third thecal pair is 0.9–1.1 mm, decreasing to 0.6–0.7 mm across the last thecal pair before the appendix. The two thecae repeat distance in the medial part of the rhabdosome is 1.6–1.8 mm. Theca 11 is much shorter than the th 12 ( Fig. 5 ). The last theca is also much shorter than the previous one ( Fig. 7B ). Thecal orifices directed laterally to proximo−laterally, geniculum list projecting ventrally beyond level of thecal lip. Pustules on the bandages are variably developed. They are relatively small on some specimens, e.g. on the distal part of rhabdosome from Bartoszyce borehole ( Fig. 6B 1 ), and from Jarosławiec ( Fig. 7D 2). The genicular hoods are densely reticulated ( Figs. 5A, B , 6A, B , 7A–D ), and the hoods totally cover the apertures, especially in mature rhabdosomes. Nema is not attached to the thecal framework.

Remarks.—The genus Neogothograptus was erected quite recently ( Kozłowska−Dawidziuk 1995), and is now known to be one of the most species−diverse retiolitid genera, being represented by nine species, one of which consists of two subspecies. The new species, N. reticulatus , along with N. eximinassa , is a member of the most densely reticulated speciesgroup of Neogothograptus with a well−developed outer ancora, dense reticulum over the entire surface, reticulum on proximal orifices, and prominent reticulated genicular hoods.

N. reticulatus shares a considerable number of morphological features with N. eximinassa . The primary difference lies in the nature of their genicular hoods: those of N. reticulatus are fully reticulated, whereas those of N. eximinassa are solid sheet−like hoods such as seen in G. nassa . A close examination of all specimens of the two species shows a clean separation between the two types of genicular hoods with no intermediate forms. A further distinction is that in N. reticulatus the outer ancora is a well developed mesh outside of the main ancora umbrella, while that of N. eximinassa may consist of only a very few thin lists.

A flattened and moderately preserved form from upper Homerian strata of Australia, and identified as Gothograptus sp. by Rickards et al. (1995), is very like N. reticulatus in its measurements, shape of rhabdosome, appendix, development of a dense reticulum, and the reticulated genicular hoods. The suggestion that the nema is incorporated into the ancora sleeve wall (Rickards et al. 1995: figs. 18K, L, 20J), is rather questionable, however. More probably, the nema is free as in all upper Homerian and Ludlow retiolitids.

The new species has some features in common with those of Gothograptus from the pre−extinction, Cyrtograptus lundgreni Biozone. Similar apertural hoods are observed in the most distal theca of the Gothograptus kozlowskii Kozłowska−Dawidziuk, 1990 ( Kozłowska−Dawidziuk 1990: fig. 4E). The apertural hoods are also reminiscent of those of G. obtectus Kozłowska−Dawidziuk, 1990 ( Kozłowska−Dawidziuk 1990: fig. 5C, D). In G. obtectus the reticulum covering the aperture is continuous along the ventral surface from thecal aperture to thecal aperture. A reticulated genicular hood and dense meshwork are also characteristic of G. storchi Lenz and Kozłowska ( Lenz and Kozłowska 2006) , although its hood does not obscure any part of the thecal orifice.

Figures

Fig. 3. SEM micrographs showing comparison of the genicular hoods of mature rhabdosomes of Neogothograptus Kozłowska−Dawidziuk, 1995 species (A–D) and Gothograptus nassa Holm, 1890 (E). A, B. Neogothograptus eximinassa Maletz, 2008, Baltic erratic boulder from Wetterhammer, Thuringia, Germany, Colonograptus ludensis–Monograptus gerhardi Biozone. C, D. Neogothograptus reticulatus sp. nov. C. ZPAL G. 41/7, Bartoszyce borehole 1630.7 m, Colonograptus praedeubeli Biozone. D. ZPAL G 41/2, Baltic erratic boulder 59, Jarosławiec, Poland. E. Gothograptus nassa, Bartoszyce borehole 1655.8 m, Pristiograptus dubius– Gothograptus nassa Biozone, whole hood (E1) and enlargement showing bandages covering hood (E2).

Fig. 5. SEM micrographs of proximal fragment of rhabdosome Neogothograptus reticulatus sp. nov., ZPAL G. 41/1, Bardo, Prągowiec, Holy Cross Mountains, Poland, Colonograptus praedeubeli Biozone. Stereopair of reverse view: ventral view of the thecae 11 side (A), stereopair of obverse view (B); outer ancora edge on thecae 12 side, ancora with outer ancora partly destroyed, view from outside (C), closure of proximal end showing outer ancora and reticulum closing orifices, obverse view (D), inside view howing thecal lip, geniculum, and med−ventral list (E), closure of proximal mid−ventral−list (F).

Fig. 6. SEM micrographs of rhabdosomes Neogothograptus reticulatus sp. nov. (A–C, E), and Colonograptus praedeubeli Jaeger, 1990 (F) from Baltic erratic boulder, Jarosławiec 59, Colonograptus praedeubeli Biozone, upper Homerian, Wenlock, Poland. A. Stereopair of lateral view of most distal end with four pairs of thecae, ZPAL G. 41/2. B. Fragment of appendix possibly belonging to Neogothograptus reticulatus, ZPAL G. 41/3. C. Stereopair of lateral view of most distal end with five thecae, with long reticulated hoods, and beginning of the appendix, ZPAL G. 41/4, lateral view (C1), view of the inside (C2). D. Lateral view of proximal end with two pairs of thecae, ZPAL G. 41/5, view of ancora from the inside (D1), enlargement of the hood list with pustules (D2). E. Enlargement of the ancora sleeve list with poorly developed pustules, ZPAL G. 41/6. F. lateral view of Colonograptus praedeubeli, rhabdosome of young colony with two thecae.

Fig. 7. SEM micrographs of rhabdosome fragments of Neogothograptus reticulatus sp. nov., Bartoszyce borehole 1630.7 m, Colonograptus praedeubeli Biozone. A. Distal end of mature rhabdosome with five pairs of thecae, and beginning of the appendix, ZPAL G. 41/7 (A1); enlargement of distal part showing long reticulated apertural hoods (A2). B. Distal end of young rhabdosome with three pairs of thecae and growing appendix, ZPAL G. 41/8 (B1); enlargement of distal part with small appendix and central nema (B2).

Fig. 1. Silurian paleogeographic map, showing occurrences of Gothograptus nassa and Neogothograptus. Localities and graptolite data derived from the following literature sources: 1, Arctic Canada: Lenz 1993; Lenz and Kozłowska−Dawidziuk 2004; 2, Nevada: Berry and Murphy 1975; 3, Southern Sweden (Baltica): Holm 1890; 4, Northeastern Poland (Baltica): Kozłowska−Dawidziuk 1995; 5, United Kingdom: Warren 1971; 6, Southern Portugal: Gutiérrez−Marco et al. 1996; 7, Southern Spain: Gutiérrez−Marco et al. 1996; 8, Thuringia (Saxothuringia): Jaeger 1991; 9, Bohemia: Kozłowska− Dawidziuk et al. 2001; 10, Kazakhstan: Koren’ et al. 2003; 11, Kyrgyzstan: (AL personal observation 1995); 12, South China: Zhang and Lenz 1997; 13, Southeastern Australia: Rickards et al. 1995; 14, Tunisia, Morocco and Libya: Waterlot 1945, Jaeger et al. 1975.