Camenella garbowskae Missarzhevsky

Kouchinsky, Artem, Bengtson, Stefan, Clausen, Sébastien & Vendrasco, Michael J., 2015, An early Cambrian fauna of skeletal fossils from the Emyaksin Formation, northern Siberia, Acta Palaeontologica Polonica 60 (2), pp. 421-512 : 457-465

publication ID	https://doi.org/ 10.4202/app.2012.0004
persistent identifier	https://treatment.plazi.org/id/03C3891D-1508-C25E-FCC9-F8DBCADBFC43
treatment provided by	Felipe
scientific name	Camenella garbowskae Missarzhevsky
status

Treatment

Camenella garbowskae Missarzhevsky in Rozanov and Missarzhevsky, 1966

Figs. 35–38 View Fig View Fig View Fig View Fig . Holotype: Sellate sclerite GIN 3470/73 ( Rozanov and Missarzhevsky 1966: pl. 11: 4).

Type locality: Near Chekurovka village , lower reaches of Lena River, northern Siberia .

Type horizon: Lower Tyuser Formation , Dokidocyathus regularis Zone, Tommotian Stage .

Material.—Over one hundred calcium phosphatic sellate and mitral sclerites, including SMNH X 4682–4699, from samples 3/0, 3/1.5, 3/5, 3/21.5, 6/0.3, 6/1.8, 6/2, 6/3.9, K6-4B, 6/4.9, K6-5.8B, 6/6.6, 6/6.8, 6/9.1, 6/14, 6/18, 7/16, and 7/19. Emyaksin Formation, Malaya Kuonamka and Bol’shaya Kuonamka rivers; Tommotian Stage. Identifiable in the collection are 46 sellates (45%) and 57 mitrals (55%), of which 59% of sellates and 51% of mitrals are of the dextral variant. Emended diagnosis.—Species of Camenella with sellate and mitral sclerites having well-developed co-marginal ribs. Sellate sclerites asymmetrical, with distinct sella separating larger and smaller lobes. Larger lobe with several radial ridges. Apex slightly coiled, up to 1/2 whorls. Duplicature in large sclerites adpressed to the inner surface laterally and near the apex. Mitral sclerites pyramidal, with well developed obplicate and accrescent sides. Plicate side with usually four pronounced radial ridges separated by deep folds. Obplicate side with several faint radial ridges and striation. Accrescent and decrescent sides without radial ridges.

Description.—Sellate sclerites ( Figs. 35 View Fig , 36 View Fig ) are asymmetrical, up to 5 mm long and 3.5 mm wide (after Missarzhevsky in Rozanov and Missarzhevsky 1966) in plan view, with a 37A). The plicate and obplicate sides bear several radial ridges, better developed on the plicate side. The ridges increase relief from the apex towards the aperture. The plicate side usually carries four well-defined radial ridges, two of which mark the boundaries with the accrescent and decrescent sides, respectively. The ridges are separated from each other by deep, narrow troughs (e.g., Fig. 37A View Fig ). By contrast, the accrescent and decrescent sides lack strong radial ridges and are covered with longitudinal striation ( Fig. 37A View Fig ). Continuous co-marginal folds cover the entire surface of sclerite. They curve towards the apex on the accrescent and decrescent sides. The internal surface is covered with smooth radial and co-marginal folds reflecting those on the exterior surface of sclerites ( Fig. 37E View Fig ). The tapering apex is circular in cross-section and exhibit a perforation, 20–100 μm in diameter (e.g., Fig. 37B View Fig 2 View Fig ).

Remarks.— Camenella reticulosa Conway Morris in Bengtson et al., 1990 is distinguished by very strong co-marginal ribs with superimposed reticulation, strong coiling and wider sella of the sellate sclerites, as well as pronounced radial ribs and intermittent folds on both plicate and obplicate sides of the mitral sclerites. The sellate sclerites in C. parilobata differ in having lobes of similar size. The mitral sclerites of Camenella garbowskae are distinguished from those of C. baltica and C. parilobata by more expressed helical twist.

Vladimir V. Missarzhevsky ( Rozanov and Missarzhevsky 1966: 96) first noted the similarity between Camenella garbowskae Missarzhevsky in Rozanov and Missarzhevsky, 1966 and Camena kozlowskii Missarzhevsky in Rozanov and Missarzhevsky, 1966 and suggested that they might represent disarticulated skeletal parts of the same organism. Further developments of terminology and taxonomy of tommotiids proposed by Bengtson (1970, 1977, 1986a) are followed here.

Less common, small sellate sclerites (both sinistral and dextral symmetry variants) with a flared margin may well also belong to the C. garbowskae scleritome (see Camenella cf. C. garbowskae in Fig. 39 View Fig ). Rare simplified, laterally compressed mitral sclerites, named “planiform” by Bengtson 1986a) after Camenella plana (Missarzhevsky in Rozanov et al., 1969), are described from Camenella baltica and C. parilobata scleritomes. Several planiform mitrals, attribut- ed herein to Camenella plana (see Fig. 40 View Fig ), co-occur with more common pyramidal mitral sclerites of C. garbowskae . The presence of planiform mitrals in the assemblage supports the suggestion by Bengtson (1986a) that such sclerites may have formed an integral part of the Camenella scleritome, but a more abundant collection of sclerites is need- ed to confirm this. Planiform mitrals occur in both sinistral and dextral symmetry variants. They are strongly flattened in accrescent-decrescent direction and curved with slight to considerable helical twist towards the descrescent side. Their plicate side carries two to three prominent radial ridges and intervening deep folds. Camenella cf. C. plana is similar to sclerites of C. garbowskae in ornamentation. The former, however, are more variable than the pyramidal mitrals of C. garbowskae and may include a different species.

The wall of Camenella sclerites consists of calcium phosphatic growth laminae.As demonstrated by the inner surface of several well-preserved mitrals of Camenella sp. from sample 6/3.9 ( Fig. 41 View Fig ), the alternating laminae are composed of more or less integrated flattened tablet-like aggregates of calcium phosphate. The tablets are not observed in other Camenella sclerites available in the collection. The mitrals of Camenella sp. are curved and more flattened in accrescent-decrescent direction than pyramidal mitrals of C. garbowskae , although less flattened than mitrals of C. plana . The ornamentation of the outer surface is also different. Nodes at intersections of radial and co-marginal ridges on all but decrescent sides produce prominent outgrowths in the apical direction. Camenella sp. occurs in dextral and sinistral symmetry variants.

Camenella admiranda (Missarzhevsky in Rozanov and Missarzhevsky, 1966) is represented by a single apical fragment of a large mitral sclerite with regularly spaced low radial ridges and distinct comarginal folds ( Fig. 42 View Fig ). Sellate sclerites of C. admiranda are not known.

Stratigraphic and geographic range.—Tommotian Stage, Siberia.

Camenella aff. C. garbowskae Missarzhevsky in Rozanov and Missarzhevsky, 1966

Fig. 43 View Fig .

Material.—Sellate sclerites: one (dextral), SMNH X 4711, from sample 6/18 and two sclerites (dextral and sinistral), SMNH X 4712 and 4713, from sample 7/16; correlated with the Dokidocyathus lenaicus Zone, Tommotian Stage. One (sinistral), SMNH X 4710, from sample 7/31.9; correlated with Delgadella anabara Zone, Atdabanian Stage. Emyaksin Formation , Bol’shaya Kuonamka River.

Description.—The sellate sclerites are asymmetrical, up to 2 mm long and 1.6 mm wide in plan view, with a sella dividing the sclerite into larger and smaller lobes. The sella occupies up to 1/3 of the sclerite width between a ridge situated on the larger lobe and a strong angulation of the margin of the smaller lobe. The ridge slightly overhangs the floor of the sella ( Fig. 43D View Fig 1 View Fig ). The larger lobe carries five very prominent radial ridges, and the entire dorsal surface of the sclerite is ornamented with distinct comarginal folds. The larger lobe is much higher than the smaller one, longer, and up to 10 times wider in plan view ( Fig. 43A View Fig 1 View Fig , A 2 View Fig ). The apex is coiled through up to 3/4 whorl ( Fig. 43C View Fig 4 View Fig , D 2 View Fig ).

Remarks.—The sclerites differ from Camenella garbowskae in having less numerous and stronger radial ribs and intervening deep folds on the larger lobe, and in a more coiled apex.

Camenella reticulosa Conway Morris in Bengtson et al., 1990 is distinguished by a superimposed reticulation of co-marginal ribs, even stronger coiling and wider sella of the sellate sclerites. The sellate sclerites in C. parilobata differ in having lateral lobes nearly equal in width. Missarzhevsky (in Rozanov et al. 1969: 169) noted morphological variability of Camenella and described forms with prominent acute radial ridges from the lower reaches of Lena River as C. garbowskae ( Rozanov and Missarzhevsky 1966: pl. 13: 11–12).