Cochlograptus veles ( Richter, 1871 )

Lenz, Alfred C. & Melchin, Michael J., 2008, Convergent evolution of two Silurian graptolites, Acta Palaeontologica Polonica 53 (3), pp. 449-460 : 450-452

publication ID	https://doi.org/ 10.4202/app.2008.0307
persistent identifier	https://treatment.plazi.org/id/BA11F872-8D6C-FF9F-DA47-D2D80A61F991
treatment provided by	Felipe
scientific name	Cochlograptus veles ( Richter, 1871 )
status

Treatment

Cochlograptus veles ( Richter, 1871)

Figs. 1A–H View Fig , 2A, B View Fig , 4C–F View Fig , 5B View Fig .

1871 Nautilus veles Richter : 243, text−fig. 1.

1883 Monograptus discus sp. nov.; Törnquist 1883: 24.

1892 Monograptus discus Törnquist ; Törnquist 1892: 39, pl. 3: 27, 28.

1913 Monograptus discus Törnquist ; Elles and Wood 1913: 439. pl. 44: 5a–d; figs 302a–c.

1965 Monograptus veles (Richter) ; Obut et al. 1956: 52, pl. 7: 2–4.

1965 Monograptus veles Richter ; Hundt 1965: figs. 93, 137, 200.

1970 Monograptus discus Törnquist ; Rickards 1970: 76, pl. 6: 8.

1971 Monograptus (Monograptus) veles (Richter) ; Schauer 1971: 59, fig. 5; pl. 35: 1–3; pl. 36: 16–18.

1975 Monograptus veles (Richter) ; Bjerreskov 1975: 71, pl. 11: D.

1975 Monograptus veles (Richter) ; Obut and Sokolevskaya 1975: 168, pl. 33: 3, 4.

1987 Cochlograptus veles (Richter) ; Obut 1987: 142, pl. 25: 5–10.

?1987 Cochlograptus chaletzkayae Obut 1987: 143 , pl. 25: 11, 12.

1988 Monograptus veles (Richter) ; Lenz 1988: 1963, fig. 5P–S.

?1993 Monograptus veles (Richter) ; Štorch and Serpagli 1993: 40, fig. 12C, E; pl. 7: 5, 7.

1994 Cochlograptus veles (Richter) ; Loydell and Cave 1994: 611, figs. 1.1–1.3, 2.

1994 Monograptus veles (Richter) ; Štorch 1994: fig. 6K.

2001 Cochlograptus veles (Richter) ; Maletz 2001: 172, fig. 3A–I.

Material examined.— About 40 specimens from talus nodule 2A, and one to three specimens from each of talus nodules 2C, 4B, and 110T, all from the Cape Sir John Franklin (76 ° 42.5’N, 96 ° 53’W), westernmost Devon Island (SJF 02); two specimens each from Cape Manning section 3, collections CM3, 6.1 m and 10.2 m (75 ° 26.8’N, 94 ° 16.7’), Cornwallis Island ; and eight specimens from the Cape Phillips type section, collection CP98, 6.4 m (75 ° 37.3’N, 94 ° 31’W), Cornwallis Island . All specimens isolated and uncompressed, and all immature GoogleMaps .

Description.—Rhabdosome tightly, ventrally, and planispirally coiled; most mature isolated study specimen with five complete thecae ( Fig. 4C View Fig ) and prothecal part of theca 6, coiled through about 270 °. Sicula total length 0.8–0.9 mm and about 0.14 mm across aperture; prosicula is 0.34–0.35 mm long. Sicula aperture with narrow, well−developed rutellum, virgella about 0.4 mm long. Junction of prosicula and metasicula rarely marked internally by annulus (see Lenz and Kozłowska−Dawidziuk 1998). Porus distal rim positioned 0.04–0.06 mm distal of sicula aperture. Sicula moderately to strongly ventrally curved, the greatest curvature being in the distal half of metasicula; tip of prosicula straight to curved ventrally. Tip of prosicula seldom fully preserved and where fully preserved may be composed only of longitudinal threads, particularly on dorsal side ( Fig. 1A View Fig ), and proximalmost tip may often be abruptly flexed ventrally. Nema often arises asymmetrically from tip of sicula or, less frequently, from the ventral side slightly below the tip, in which case the extreme tip of sicula is distally projected as a small, mound−like protuberance ( Fig. 1B View Fig 2 View Fig , E, G). In rare specimens, a pseudovirgula emerges from a point below the tip of the prosicula ( Fig. 4F View Fig 1 –F View Fig 3 View Fig ) and replaces the nema as the growth axis along the dorsal side of the rhabdosome. In either case, nema or pseudovirgula is sharply deflected ventrally at angle of 45–60 ° to longitudinal axis of sicula ( Fig. 1B, F, H View Fig ; see also Maletz 2001: fig. 3G, H). Apex of sicula attains level from midway between thecae 1 and 2 to, most commonly, about level with thecal hood of theca 2. Thecae multiform. Theca 1 arises 0.04–0.06 mm from sicular aperture; metatheca relatively long and strongly curved through about 180 ° so that aperture fully directed proximally. Theca 2 metatheca somewhat less strongly curved than theca 1, aperture directed slightly proximo−ventrally. Theca 3, arising after the strong ventral deflection of the nema or pseudovirgula, typically possesses an unusually long protheca to compensate for strong and abrupt flexure. More distal thecae with smoothly and uniformly curved dorsal walls, with relatively short, triangular prothecae and long, strongly curved metathecae in which the apertures of thecae directed ventro−proximally, and lateral profiles of distal metathecae are triangular. Amount of curvature and thecal overlap gradually decreases distally. Thecal apertures ovate in cross section, apertural rim smoothly curved with slightly thickened margin. Thecal spines about 0.3–0.4 mm long at lateral margin of apertural hood, directed laterally or slightly ventro−laterally. Thickened interthecal septum (see Lenz and Kozłowska−Dawidziuk 1998) well developed ( Fig. 2A View Fig 4 View Fig , B 2 View Fig ). Interthecal septum curved, angle of its junction with dorsal wall of rhabdosome is somewhat variable but approximately 600 throughout the length of the rhabdosome. Thecal overlap 25–30% of total thecal length, decreasing somewhat distally. Proportion of rhabdosomal width occupied by free metathecal portions about 50% throughout. 2TRD approximately 1 mm from second to fourth thecae; width at theca1 about 0.5 mm, and 0.6 mm at theca 5 (one specimen).

Remarks.—Although Obut (1987) assigned this species to the subgenus Cochlograptus, Loydell and Cave (1994) and Maletz (2001) accorded it full generic status, a practice followed in this paper. Cochlograptus veles (and its junior synonym “ Monograptus ” discus ), has been recorded from many regions in the world: Germany ( Richter 1871; Hundt 1965; Schauer 1968; Maletz 2001), Scandinavia ( Törnquist 1892; Bjerreskov 1975; Maletz 2001), British Isles ( Elles and Wood 1913; Rickards 1970; Hutt 1975; Loydell and Cave 1994), southern Mackenzie Mountains, Canada ( Lenz 1988), Canadian Arctic Islands ( Melchin 1989), Taimyr, Russia; Central Asia ( Obut et al. 1965; Obut and Sobolevskaya 1975; Obut 1987), Czech Republic ( Štorch 1994), Poland ( Tomczyk et al. 1990) and, questionably, Sardinia ( Štorch and Serpagli 1993), from which the specimens show a much looser ventral curvature. All of the specimens, except for the three isolated specimens from Sweden illustrated by Maletz (2001), have been either preserved as flattened films on shale surfaces or, occasionally, shown in slight relief. In either case, details of the sicula, thecae, and early rhabdosomal development have been poorly understood. This is especially true in the case of mature flattened material, where more extended development of the rhabdosome completely obscures details of the early proximal development.

The genus Cochlograptus was erected by Obut (1987), who considered the tightly coiled, discoid nature of the rhabdosome to be the definitive generic character. He recognized the Monograptus priodon −like shape of the thecae with their pronounced, laterally projecting spines, and noted the similarity of the new genus to Testograptus testis from which it is distinguished in being totally discoid−shaped, and in being much smaller. However, in all earlier studies of flattened specimens of the species, including those studied by Obut (1987), there was little to indicate that the dorsal wall margin was other than a smoothly rounded spiral throughout or, if observed, this was ignored or unappreciated. This lack of appreciation was most probably due to the fact that all previously studied and illustrated forms were flattened and more mature, in which case, early rhabdosome growth was obscured by later development.

Loydell and Cave’s (1994) study of several immature specimens of Cochlograptus veles was the first to illustrate its unusual development, wherein the nema and the tip of the prosicula are free, and a pseudovirgula, appearing and diverging strongly from a point near the tip of the sicula, performs the same post−sicular functions as the true nema for all remaining thecae subsequent to the formation of thecae 1 and 2. Maletz (2001) illustrated some specimens from Richter’s (1871) original material, selected a lectotype from another slab collected by Richter and, importantly, illustrated three immature, isolated specimens from Sweden. Two of these specimens (e.g., Maletz 2001: fig. 3G, H) clearly show the free tip of the sicula and nema, although much less of the sicular tip is exposed than for the specimen illustrated by Loydell and Cave (1994). This may, however, be the result of continued growth of the triangular web of material in the early growth stage shown in Loydell and Cave (1994: fig. 1.3). These specimens also demonstrate the sharp angle between the pseudovirgula and the sicula−nema axis.

The Arctic collections, while numerous, are made up of entirely immature specimens, with no specimen possessing more than five fully−developed thecae and the protheca of theca 6. The fact that Cochlograptus veles (as well as Testograptus testis ) develop with a “normal” nema as well as, occasionally, by means of pseudovirgula, suggests that both modes of growth are part of the normal range of variation within these two species. It demonstrates, moreover, the “plasticity” and the adaptability of graptolites in their overall astogenetic development.

Rickards, Hutt and Berry (1977) suggested that “ Monograptus discus ” (= Cochlograptus veles ) may have been commonly helically spiralled. The many isolated specimens from the Arctic, the isolated Swedish specimens with at least six fully−developed thecae ( Maletz 2001), the well−preserved, and much more mature specimen (with more than 20 thecae) illustrated by Bjerrreskov (1975), and the dozens of flattened specimens illustrated in Hundt (1965) suggest, however, that C. veles was totally planispiral. Alternately, if the species was helically spired, the spire would have been exceedingly shallow.

Kingdom	Animalia
Phylum	Hemichordata
Class	Pterobranchia
Family	Monograptidae
Genus	Cochlograptus