Plectograptus Moberg and Törnquist, 1909

Kozłowska-Dawidziuk, Anna, 2002, Agastograptus, a synonym of Plectograptus (Retiolitidae, Graptolithina), Acta Palaeontologica Polonica 47 (3), pp. 459-467 : 460

Genus Plectograptus Moberg and Törnquist, 1909

Type species: Retiolites macilentus Törnquist, 1887 , from Wetterhammer area (Colonusskiffern), Thüringia, Ludlow.

Emended diagnosis.—Ancora umbrella simple, small, usually partly preserved. Sicula about 2.6 mm long, rarely preserved as traces of the prosicular rim, and indicated by seams on the virgella. Nema free, possibly extended as a nematularium in mature specimens. Ancora sleeve lists of hexagonal meshes with zigzag pattern in the mid−dorsal part of wall. First zigzag lists of ancora sleeve located in region of the lips of th 11 and th 12. Large proximal orifices on obverse and reverse sides of rhabdosome, outlined by the ancora umbrella lists (rarely preserved), and first zigzag lists of the ancora sleeve. Mid−ventral list present. Ancora sleeve and thecal lists with seams from the inside and distinctive pustules on bandages.

Species included.— Plectograptus macilentus ( Törnquist, 1887) , P. robustus ( Obut and Zaslavskaya,1983) , P. wimani ( Eisenack, 1951) .

Discussion.—The type species Plectograptus macilentus ( Törnquist, 1887) was originally assigned to the genus Retiolites , based on poor material from Thüringia. Moberg and Törnquist (1909) established a new genus Plectograptus for R. macilentus , following the study of better preserved material from Skåne, Sweden. They illustrated a flattened type specimen of P. macilentus with large proximal openings ( Moberg and Törnquist 1909: pl. 1: 10). The main diagnostic features of large proximal orifices as well as paired reticulofusellar apertural processes occur in one species of Plectograptus , P. robustus . Similar processes are characteristic of species of Spinograptus (see Kozłowska−Dawidziuk 1997), including S. clathrospinosus from the Colonograptus praedeubeli Biozone which precedes the appearance of P. robustus and P. macilentus , both of which occur in the Ludlow Neodiversograptus nilssoni Biozone. Spinograptus is considered to be an ancestor of Plectograptus ( Kozłowska−Dawidziuk 1995) . The main differences between these two genera are the presence in Plectograptus of large lateral proximal orifices, and a nematularium. Nematularia have only been found in flattened material ( Moberg and Törnquist 1909; Eisenack 1951; Bouček and Münch 1952; Tomczyk 1956). The rhabdosome of Spinograptus typically tapers distally, and in most species ends with an appendix ( Lenz 1994a; Kozłowska−Dawidziuk 1997).