Camenella Missarzhevsky, 1966

Skovsted, Christian B., Balthasar, Uwe, Brock, Glenn A. & Paterson, John R., 2009, The tommotiid Camenella reticulosa from the early Cambrian of South Australia: Morphology, scleritome reconstruction, and phylogeny, Acta Palaeontologica Polonica 54 (3), pp. 525-540 : 528-529

Genus Camenella Missarzhevsky, 1966

1966 Camena Missarzhevsky gen. nov.; Rozanov and Missarzhevsky 1966: 93. [non Martens in Albers and Martens 1860; Hewitson 1865]

1966 Camenella Missarzhevsky gen. nov.; Rozanov and Missarzhevsky 1966: 95.

1970 Tommotia nom. nov.; Missarzhevsky 1970: 100.

Type species: Camenella garbowskae Missarzhevsky, 1966 , Tommotian

Stage ( Dokidocyathus regularis Zone ), Chekurovka village, Siberia.

Emended diagnosis.—Tommotiids with solid, densely lamellar sclerites. Surface sculpture of fine growth striae, larger co−marginal ribs and occasional transverse ribs radiating from the umbo. Two types of sclerites; pyramidal mitrals and saddle shaped sellates. Mitral sclerites with subquadrate cross−section, a pointed umbo and a system of pronounced radiating folds on one or occasionally two opposing sides. Sellate sclerites strongly asymmetrical and compressed with marginal, sometimes coiled apex, dorsal surface with two lobes of unequal size separated by a depressed sella and ventral surface often with distinct duplicature. Both sclerite types occur in dextral and sinistral symmetry variants. Differs from Lapworthella and related genera by the presence of two distinct sclerite types, and from Dailyatia and Kennardia by the absence of bilaterally symmetrical sclerites.

Species included.—See Bengtson (1986) for a comprehensive discussion of the nominal species included in Camenella . To this list can be added Camenella reticulosa Conway Morris, 1990 .

Discussion.—The genus Camenella appeared in the early Tommotian of Siberia ( Rozanov et al. 1969). The genus has also been recovered in lower Cambrian rocks from Baltica ( Bengtson 1970) , Avalonia ( Bengtson and Fletcher 1983), Mongolia ( Bengtson 1986) and Australia ( Bengtson et al. 1990 and herein). It has two distinct sclerite types (sellate and mitral, Fig. 2 ; terminology following Bengtson 1970) which were originally described as separate genera by Missarzhevsky ( Camena [mitrals] and Camenella [sellates] in Rozanov and Missarzhevsky 1966). Because of homonymy, the genus Camena was later renamed Tommotia ( Missarzhevsky 1970) , resulting in considerable taxonomic and nomenclatural confusion (reviewed in Bengtson 1977, 1986). Although some authors have persisted in separating Camenella and Tommotia ( Meshkova 1969; Repina et al. 1974; Grigorieva in Voronin et al. 1982; Missarzhevsky 1989; Vasilieva 1998), all available evidence, including the new material from South Australia described here, supports the unified model of one scleritome encompassing two distinct sclerite types.

The list of nominal species of Camenella is likely to be substantially inflated due to the lack of appreciation in early systematic works of the multi−component nature of the Camenella scleritome and the variability of sclerites ( Bengtson 1977, 1986). Only three species, Camenella baltica , C. parilobata , and now C. reticulosa have been described using a scleritome based model, and all other species require re−evaluation. In the following discussion of C. reticulosa , it should be noted that mitral and sellate sclerites of many of these species were described separately under the generic names Tommotia (mitral sclerites) and Camenella (sellate sclerites), respectively. However, even in these cases it is sometimes possible to identify specific pairs of sclerites that probably belonged to a single scleritome. Until reinvestigations of relevant type material has been carried out, no formal synonymy can be proposed.

Stratigraphic and geographic range.—Lower Cambrian (Tommotian to Botoman and equivalents) of the Siberian Platform, western Mongolia, South Australia, Baltica ( Sweden) and Avalonia ( England, Newfoundland, Nova Scotia).

Figures

Fig. 2. Tommotiid Camenella reticulosa Conway Morris, 1990, from lower Cambrian Hawker Group, Flinders Ranges, Arrowie Basin, South Australia explanation of terminology. A, B. Sellate sclerites. A. SAMP 43172 (dextral), Wilkawillina Q, in dorsal view. B. SAMP 43178 (dextral),Wilkawinnina Q, in ventral view. C. Mitral sclerite, SAMP 43167 (sinistral), MMF 0.0, in apical view.