Sphenothallus sica: A branching Conularid from the Early Devonian of Brazil.

The Conularids are an enigmatic group of organisms with possible affinities to the Cnidarians, which first appeared very close to the beginning of the Cambrian (or possibly at the End of the Ediacaran), and disappeared in the Early Triassic. They form cones comprised of concentric disks stacked within one another; these disks have four-fold radial symmetry, as is seen in modern Jellyfish, and it has therefore been suggested that the Conularids may represent something similar to the Attached Medusa stage of the living Stalked Jellyfish, Stauromedusae, from which new free-swimming Jellyfish arise by budding off.

In a paper published in the journal Acta Palaeontologica Polonica on 3 April 2019, Heyo Van Iten of the Department of Geology at Hanover College, and the Department of Invertebrate Paleontology at the Cincinnati Museum Center, Juliana de Moraes Leme of the Department of Sedimentary and Environmental Geology at the University of São Paulo, Marcello Simões of the Department of Zoology at São Paulo State University, and Mario Cournoyer of the Musée de Paléontologie et de l’Évolution, describe a new species of Conularid from the Early Devonian Ponta Grossa Formation of Paraná State in Brazil.

The description of the new species is based upon specimens first described by the palaeontologist John Mason Clarke in 1903, and which he identified as a problematic fossil, and possibly a Hydroid, which he named Serpulites sica, and later redescibed by Friedrich Sommer in 1954 as an algae, which he named Euzebiola clarkei. Van Iten et al. accept Clarke's specific name, sica, but refer the specimen to the Conularid genus Sphenothallus, on the basis of that it apparently has a soft body covered by a tubular or steeply pyramidal organic or organo-phosphatic periderm with fine laminations, that this periderm ends in a sub-conical expansion, and exhibits a transverse internal wall.

Medusozoan Cnidarian Sphenothallus sica from the Early Devonian Ponta Grossa Formation, Paraná State, southern Brazil. The numbers 1–16 indicate the evident, marginal daughter tubes, while the letter P indicates the parent tube. (A) Reproduction of Clarke’s (1913) drawing. (B) Light photographs. (B₁), general view; 17?, the possible basal portion of a seventeenth daughter tube; (B₂), detail, the arrow indicates a short longitudinal cross section through one of the marginal thickenings. Also present, near this site, is apparent spalling of fine lamellae. Scale bars: (A), (B₁) 16 mm; (B₂) 4 mm. Van Iten et al. (2019).

The specimen comprises a partial branching periderm about 40 mm long and bearing at least 16 variably curved daughter tubes. Two of the daughter tubes originate at the widest point of the parent, while the remaining daughter tubes are arrayed in single file along each side. Both the daughter and parent tubes are narrowest at the base and widen towards the tips. This pattern of branching is similar to that seen in modern Cnidarians such as the Hydrozoan Eudendrium ramosum, or Scyphozoans such as Stephanoscyphus racemosus, which Van Iten et al. regard as evidence supporting the proposed relationship between the Conularids and the Cnidarians.

The extant Scyphazoan Nausitho punctata. Chapman & Werner (1972).

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Possible Annelid Worm tubes from the Early Devonian of Brazil.

Worm tubes first appear in the fossil record in the Ediacaran and become increasingly common through the Palaeozoic. Most Worm tubes today are made by Polychaete Annelids, a group which have existed since at least the Cambrian, however in the Palaeozoic a variety of other groups, such as Tentaculitoids (thought to have been related to Molluscs and Lophophorates) and Hyolithelminths (possibly Cnidarians) are known to have made tubular structures, making it difficult to assess when tube-building Polychaetes first appeared.

In a paper published in the journal Acta Palaeontologica Electronica on 21 December 2015, Olev Vinn of the Department of Geology at the University of Tartu, Carolina Zabini and Gustavo Sene-Silva of the Universidade Tecnológica Federal do Paraná, Kalle Kirsimäe also of the Department of Geology at the University of Tartu and Lara Susan-Marcos, also of the Universidade Tecnológica Federal do Paraná, describe a series of tubes from the Early Devonian Ponta Grossa Formation of Paraná State in Brazil.

The tubes are fragmentary and have been reworked prior to preservation in sediment, The sample examined contains about 50 such tubes with a maximum length of 2.5 cm. They are 2.9–5.8 mm in width and eliptical, though this is thought to be due to compression. They are banded, with seven-to-ten rings every 5 mm, and do not taper or branch. Vinn et al. describe these as Annulitubus mutveii, where 'Annulitubus' means 'ringed-tube' and 'mutveii' honours palaeontologist Harry Mutvei for his work on the skeletal structures of extinct invertebrates.

Sample (MN 9571-I) from Rio Caniú outcrop, Ponta Grossa Formation, Upper Emsian, Lower Devonian. (A) Fragment showing numerous tubes; holotype of Annulitubus mutveii  (MN 9571-Ia) and paratypes (MN 9571-Ib–e). Note that all tube fragments are straight and have similar orientation, some show smooth surfaces, with very subtle striae, in others it is possible to see shallow rings. (B) Enlarged holotype (MN 9571-Ia), note the smooth rings. (C) Fragment showing paratype (MN 9571-Ig). Vinn et al. (2015).

The Worms are interpreted as having grown close to the site of deposition, probably in dense clusters but not attached to one-another. The locality is not thought to have had any solid rock close by, but shells were available and could possibly have served as points of attachment, or the worms could have lived and formed tubes partially or wholey within the sediment. The tubes are preserved in silica, a mineral not known to have been used to make tubes by any Worm group, and therefore Vinn et al. interpret this as a secondary material which has replaced the original tube material. Silica requires very alkaline conditions to form, conditions under which calcite tubes would be expected to lose much of their original structure, leading Vinn et al. to suggest that the tubes were originally formed from organic material rather than mineral. Such a structure, with non-tapering, non-branching organic tubes with a banded structure is typical of several Polychaete groups, but not associated with any non-Polychaete group, leading Vinn et al. to conclude the tube-builder was almost certainly a Polychaete.

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