Spinograptus tubothecalis, Kozłowska & Dobrowolska & Bates, 2013

Kozłowska, Anna, Dobrowolska, Kinga & Bates, Denis E. B., 2013, A new type of colony in Silurian (upper Wenlock) retiolitid graptolite Spinograptus from Poland, Acta Palaeontologica Polonica 58 (1), pp. 85-92 : 88-91

publication ID	https://doi.org/ 10.4202/app.2011.0020
persistent identifier	https://treatment.plazi.org/id/4331BC17-FFDB-9C00-A119-FEE4FA991ACE
treatment provided by	Felipe
scientific name	Spinograptus tubothecalis
status	sp. nov.

Treatment

Spinograptus tubothecalis sp. nov.

Figs. 2A, B, D, E View Fig , 3A–D View Fig , 4 View Fig .

Etymology: From Latin tubo, tube and theca, theca; due to the shape of the two last thecae.

Type material: Holotype ZPAL G. 47/1, stub 18b, Figs. 2A View Fig , 3C View Fig ; paratype ZPAL G. 47/6, stub 324, Fig. 4A View Fig .

Type locality: Gołdap IG−1 borehole, depth 1267.0 m, Poland, East European Platform .

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

Referred material.—The well preserved isolated, slightly flattened specimens come from two localities: the Gołdap IG−1 borehole, depth 1267.0 m and a nodule from Prągowiec 2, Holy Cross Mountains, Poland. Gołdap IG−1 contains one finite rhabdosome and 65 fragments, mostly proximal parts of young and mature rhabdosomes of S. tubothecalis sp. nov.; Plectograptus robustus , and monograptids: Colonograptus deubeli , Pristiograptus dubius ludlowensis , Pristiograptus ludensis , representing the Colonograptus deubeli Biozone. From the second location, Prągowiec 2, are 800 specimens, mostly of the medial part of rhabdosomes, several proximal and distal ones, together with Neogothograptus reticulatus Kozłowska, Lenz, and Melchin, 2009 ; Plectograptus ? and Colonograptus colonus , representing the Colonograptus praedeubeli Biozone.

Diagnosis.—Parallel−sided, densely reticulated rhabdosome terminated by small appendix located between two distal thecae. Rhabdosomes contain three to four pairs of thecae. Pre−thecal ventral orifices with paired short, apertural processes; in mature rhabdosomes orifices may be overgrown by reticulum. Paired reticulofusellar apertural processes similar to Spinograptus clathrospinosus . Two distal thecae tube−shaped, and isolated, having rounded openings built by lip, lateral apertural rod and geniculum without processes. Reticulated outer ancora present in some specimens. Nema free through rhabdosome except species with finite rhabdosomes where most distal part of nema is included in the appendix wall.

Description.—The holotype ZPAL G. 47/1, a well preserved finite rhabdosome, is 2.64 mm long, and bears three pairs of thecae ( Figs. 2A View Fig 1 View Fig , 3C View Fig ). There are some fragments, especially from Prągowiec 2, indicating rhabdosomes with four pairs of thecae. It is about 1 mm wide between the pre−thecal ventral orifices, and about 0.93 mm between the second pair of thecae. The ancora umbrella is asymmetric, typical for Spinograptus , with proximal lateral orifices located on th 12 side ( Fig. 2A View Fig 1 View Fig , A 2 View Fig ). The reticulum on the ancora umbrella, as well as on the outer ancora is developed only on the th 11 side, mainly in mature rhabdosomes in specimens from Gołdap ( Fig. 2A View Fig 4 View Fig , B 1 View Fig , D). The reticulum is denser in specimens from Gołdap than from Prągowiec 2 (see Figs. 2A, B, D View Fig , 4 View Fig ). The pre−thecal ventral orifices have paired processes half the size of the thecal processes. The orifices are sometimes overhttp://dx.doi.org/10.4202/app.2011.0020

grown by reticulum ( Fig. 2B View Fig 1 View Fig , D). The apex of the well preserved sicula reaches to the end of second pair of thecae; the length of sicula is 1.1 mm. The two first pairs of thecae have paired reticulofusellar processes about 0.7 mm long. The last theca in the holotype is developed as a partly isolated tube with rounded openings made by the genicular, pleural and thecal lip lists without paired apertural processes ( Fig. 2A View Fig 1 View Fig ). The specimens from Prągowiec 2 have two distal thecae ( Fig. 4 View Fig ) similarly developed as the last theca in the holotype. The isolated parts of the distal thecae are about 0.5 mm long. Between the distal thecae is a small appendix of about 60 µm diameter ( Figs. 2A View Fig 1 View Fig , 4A View Fig ). In a young specimen with one theca developed the outer ancora has already started to grow ( Fig. 2E View Fig ). Mid−ventral lists are short, developed only at the first pair of thecae ( Fig. 2A View Fig 1 View Fig ). The rudimentary transverse rods are at first pair of thecae ( Fig. 2B 2 View Fig ). The dense reticulum of the ventral walls makes it difficult to check the presence of transverse rods in the most distal thecae. The nema is free up to the appendix, where it is attached to the wall on the obverse side of the rhabdosome ( Figs. 2A View Fig 1 View Fig , A 3 View Fig , 4A, B View Fig 3 View Fig ). Very

dense reticulum occurs in mature rhabdosomes, developed in the thecal and ancora sleeve walls ( Fig. 2A View Fig 1 View Fig ). Among specimens from both localities there are several with the sicular and thecal membranes preserved ( Fig. 3A–D View Fig ).

Discussion.—The distal end of the new species differs from that in other species of Spinograptus . The last two thecae, partly isolated, have unusual rounded openings without genicular processes ( Figs. 2A View Fig 1 View Fig , A 3, 3B, C View Fig , 4A, B View Fig 1 View Fig , B 2 View Fig ). Such openings are unique among all retiolitids. The rudimentary appendix in the new form is similar to that in other species of Spinograptus with appendixes, but does not extend more distally than the last thecae.

Spinograptus tubothecalis sp. nov. belongs to the older group of Spinograptus species, occurring in Colonograptus praedeubeli and C. deubeli biozones ( Fig. 1 View Fig ). Most of them have, unusually for the retiolitids, well preserved peridermal membranes, both thecal and ancora sleeve ( S. lawsoni , S. latespinosus , S. reticulolawsoni , S. praerobustus , and S. tubothecalis sp. nov.). This kind of preservation does not usually occur in other retiolitids ( Lenz 1994a, b; Kozłowska−Dawidziuk 1997; Lenz and Kozłowska−Dawidziuk 2002). The new species probably had an ancora sleeve membrane ( Fig. 5 View Fig ), which was too thin to be preserved.

Finite rhabdosomes occur in four species of Spinograptus together with the new one; the new species representing at the same time the new type of the finite rhabdosome. The new species is similar to S. reticulolawsoni Kozłowska−Dawidziuk, 1997 in having a finite colony ended by a short, rudimentary appendix. The most significant difference is in the sides of the finite rhabdosomes, which taper distally in S. reticulolawsoni and are parallel in the new species ( Fig. 1 View Fig ).

The older species of Spinograptus : S. reticulolawsoni , S. latespinosus , and S. clathrospinosus have a dense reticulum. The new species S. tubothecalis has the densest reticulum of all the Spinograptus species, not only on the ancora umbrella and the thecal and ancora sleeve walls, but the reticulum of the outer ancora is also much denser than in other species, e.g., S. clathrospinosus , and is located at the th 11 side of rhabdosome ( Fig. 2C 2 View Fig ). The pre−thecal ventral orifices are sometimes overgrown by dense reticulum. Among Spinograptus species the paired genicular processes, present in the new species, occur also in S. spinosus and S. clathrospinosus . Another feature of the new species is the presence of a rudimentary transverse rod, which is characteristic in pre− Cyrtograptus lundgreni retiolitids.

Geographic and stratigraphic range.—Gołdap IG−1 borehole, East European Platform, and Prągowiec 2, Holy Cross Mountains, Poland; Colonograptus deubeli Biozone and Colonograptus praedeubeli Biozone respectively.

ZPAL	Zoological Institute of Paleobiology, Polish Academy of Sciences

Copyright notice

No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.

Taxonomy

Kingdom	Animalia
Phylum	Hemichordata
Class	Pterobranchia
Family	Retiolitidae
Genus	Spinograptus