Camenellan

The camenellans, consisting of the genera Camenalla, Dailyatia, Kennardia, Kelanella and Lapworthella, are a (probably monophyletic) group of Tommotiid invertebrates from the Cambrian period, reconstructed as sister to all others (plus brachiopods and phoronids). They are known from isolated sclerites, but are believed to have a scleritomous, Halkieria-like construction.[2][3]

Camenellan Temporal range: Early Cambrian PreꞒ Ꞓ O S D C P T J K Pg N
Diagrammatic reconstruciton of the scleritome of Dailyatia bacata, after Skovsted et al 2015
Scientific classification
Kingdom:	Animalia
Clade:	Lophophorata
Order:	†"Tommotiida"
Informal group:	†Camenellans
Genera
Camenella Missarzhevsky in Rozanov & Missarzhevsky, 1966 Dailyatia Bischoff 1976 Kelanella Missarzhevsky in Rozanov & Missarzhevsky, 1966; = Bengtsonia, Tesella, Sonella[1] Kennardia Laurie, 1986 Lapworthella Shetlandia Wrona, 2004

Dailyatia and Camenella have distinct dorsal (symmetrical) and lateral (asymmetric) sclerite morphologies. The same has been asserted for Lapworthella[4] even though that has not always been the common perception.[3]

It has been argued that Camenella, Kelanella and Lapworthella, assuming a slug-like anatomy, had an anterior 'head valve' followed by pairs of asymmetric valves running in pairs along their dorsal surface.[4]

The 'head valve' in Lapworthella - that is the bilaterally symmetric Morph A valve - is thought to have fused from two ontogenetically separate sclerites.[4] Dailyatia has a similar double-mounded structure at the tip of its A type sclerites.[2]

Growth rings in all are marked out by prominent external ridges.[2][4]

Taxonomy

Two families:[2]

Kennardiidae Laurie 1986: three sclerite morphs, one of which (conventionally termed the A morph) is bilaterally symmetrical, the other two occurring in sinistral and dextral variants. Includes Kennardia and Dailyatia, and questionably Shetlandia

Lapworthellidae: sclerites occur in something of a morphological continuum, but essentially form a single type with a sinistral and dextral version, possibly with the anterior-most pair of sclerites fusing into a single bilaterally-symmetrical, dual-tipped sclerite.

Dailyatia species:[2]

• D. ajax Bischoff 1976 (type)
• D. bacata Skovsted et al 2015
• D. braddocki Evans & Rowell 1990
• D. decobruta Betts 2019[5]
• D. helica Skovsted et al 2015
• D. macroptera (Tate 1892)
• D. odyssei Evans & Rowell 1990

References

1. Devaere, L. et al. The tommotiid ~Kelanella~ and associated fauna from the early Cambrian of southern Montagne Noire (France): implications for camenellan phylogeny. Palaeontology 57, 979–1002 (2014).
2. Skovsted, C. B., Betts, M. J., Topper, T. P. & Brock, G. A. The early Cambrian tommotiid genus ~Dailyatia~ from South Australia. Mem. Assoc. Australas. Palaeontol. 48, 1–117 (2015).
3. Murdock, D. J. E., Donoghue, P. C. J., Bengtson, S. & Marone, F. Ontogeny and micro-structure of the enigmatic Cambrian tommotiid ~Sunnaginia~ Missarzhevsky, 1969. Palaeontology 55, 661–676 (2012).
4. Devaere, L. & Skovsted, C. B. New early Cambrian sclerites of ~Lapworthella schodakensis~ from NE Greenland: advancements in knowledge of lapworthellid taxonomy, sclerite growth and scleritome organization. Geol. Mag. (2016). doi:10.1017/S0016756816000698
5. Betts, Marissa; Claybourn, Thomas; Brock, Glenn; Jago, James; Skovsted, Christian; Paterson, John (2019). "Early Cambrian shelly fossils from the White Point Conglomerate, Kangaroo Island, South Australia" (PDF). Acta Palaeontologica Polonica. 64 (3). doi:10.4202/app.00586.2018.