Sphenothallus sica ( Salter, 1856 )

Iten, Heyo Van, Leme, Juliana De Moraes, Simões, Marcello G. & Cournoyer, Mario, 2019, Clonal colony in the Early Devonian cnidarian Sphenothallus from Brazil, Acta Palaeontologica Polonica 64 (2), pp. 409-416 : 412-414

publication ID	https://doi.org/ 10.4202/app.00576.2018
persistent identifier	https://treatment.plazi.org/id/AA7AF95C-9968-116F-FCD7-FAD1FA05FC50
treatment provided by	Felipe
scientific name	Sphenothallus sica ( Salter, 1856 )
status

Treatment

Sphenothallus sica ( Salter, 1856)

Figs. 4 View Fig , 5 View Fig .

1856 Serpulites sica ; Salter 1856: 222, pl. 25, 19.

1913 Serpulites sica Salter, 1856 ; Clarke 1913: 85–86, pl. 26: 15–18. 1954 Euzebiola clarkei ; Sommer 1954: 178, pl. 15: 2.

1992 Sphenothallus sica (Salter) ; Van Iten et al. 1992: fig. 3.

Material.— DPNM 329, the branching specimen ( Figs. 4 View Fig , 5 View Fig ). DPNM 1, association of five partial tubes; from the Jaguariaíva Member (Pragian–Emsian) of the Lower Devonian Ponta Grossa Formation near Ponta Grossa, Paraná State, Brazil.

Description.—Periderm fragments measuring up to about 145 mm long ( DPNM 1) and a partial branching periderm measuring about 55 mm long and 32 mm wide ( DPNM 329). Branching periderm consists of a single, very gently tapered parent tube (labelled “P” in Fig. 4A, B View Fig 1) measuring about 40 mm long and bearing at least 16 variably curved daughter tubes ( Fig. 4 View Fig : 1–16); two of the daughter tubes (1, 2) originate at the wide of the parent, while the remaining daughter tubes (3–16) are arrayed in single file along each of the two lateral margins of the parent, in a manner resembling opposite or sub-opposite branching in plant stems. Additional tube fragments, at least some of which probably belong to certain of the numbered daughter tubes, are also present. Guyot-like basal portion of at least two additional daughter tubes ( Fig. 5A View Fig 1) present on the exposed face of the parent tube near its wide end. Periderm black, apparently organic and possibly laminated, in transverse cross-sections sub-elliptical. Periderm of the daughters confluent with that of the parent, the apical end of which has been truncated. Gently curved apertural margin may be preserved at the distal end of three of the daughter tubes (1–3). Marginal thickenings preserved as narrow, levee-like berms or as trough-like external molds. Internal schotts and basal attachment discs not observed.

Remarks.—In agreement with the present description of DPNM 1 and DPNM 329, Clarke (1913: 85–86) states that these specimens consist of “chitinous [organic] tubes which may in their original state have been flat, as they are always reinforced by two chitinous cords at the margins, the connecting tissue being relatively thin.” Clarke (1913: 320) further states that the “cords are often found alone, the more tenuous parts having been torn away.” Re-examination of Clarke’s (1913) material ( Figs. 4 View Fig , 5 View Fig ) confirms most of these statements. Thus, inspection of broken ends and missing portions of the exposed face (e.g., Figs. 4B View Fig 2 View Fig , 5A View Fig 1) shows that the tubes are hollow, with the former cavity now being filled with rock matrix, and that the transverse cross-section of the tubes is sub-elliptical. The “cords” noted by Clarke 1913) appear on external molds as a pair of shallow troughs, and in places where skeletal material of the exposed face is preserved, they are expressed as one or two low, narrow, levee-like berms ( Fig. 5A View Fig 3 View Fig ). This preservational feature likely developed during compaction when the more resistant marginal thickenings retained their relief in contrast to the thinner and more readily deformable faces. Moreover, in some of the places (e.g., Fig. 4B View Fig 2 View Fig ) where the tube has been broken and is thus visible in cross-sections, the marginal portion of the tube is noticeably thicker than across the faces. Finally, Salter (1856: 222) stated that material from the Devonian Bokkeveld Group of South Africa exhibited “striae of growth” that “are conspicuous and oblique”; however, and as previously suggested by Clarke (1913: 86), we think that these features may actually be secondary wrinkles.

Present near the wide and, presumably, youngest end of the parent tube of DPNM 329 are at least two, guyot-like protuberances that occur between the raised margins, in the middle of the thin exposed face ( Fig. 5A View Fig 1). Clarke (1913: pl. 26: 18) shows two additional guyot-like structures, both located on the exposed face between daughter tubes 3 and 4, but we did not see such features on that part of the parent tube. One of the guyot-like features we did see is situated between daughter tubes 5 and 6 ( Fig. 5A View Fig 1), while the second such structure occurs between tubes 7 and 8. Again in agreement with Clarke (1913), we suspect that a fourth, similar feature occurs at these same two levels on the still covered, opposite face of the parent tube. If this hypothesis is true, then at least some of the daughter tubes are arranged in whorls or “verticil[s]” ( Clarke 1913: 319) consisting of four iso-latitudinal daughters. All of the tubes are incomplete, and some of the daughter tubes (7, 12 and 13) consist only of the basalmost portion.The narrow apical end of the parent tube is truncated, and there is no evidence of a holdfast or stolon. The free wide end of daughter tubes 1–3 is gently curved and approximately perpendicular to the lateral margins; thus, these three tubes may preserve the apertural margin. Unfortunately, the counterpart of DPNM 329 either was not collected or is missing, and as noted above the entire specimen is coated with a transparent lacquer-like substance that cannot be removed without destroying the specimen. Most of the tubes, including the parent, consist of short stretches of complete periderm (preserving the marginal thickenings and, probably, both of the two thin walls between them) alternating with stretches missing the exposed face (presumably present on the missing counterpart specimen) or consisting of an external mold (e.g., Fig. 4B View Fig 2 View Fig ). Daughter tubes 1–8 and 12–13 are arranged in opposition or near opposition, with three of these pairs (comprising daughters 3–8) being separated from each other by approximately 3 mm. Furthermore, daughter tubes 1 and 2 originate at the wide end of the parent, which thus resembles a plant stem exhibiting dichotomous branching at its tip. The external surface of the expanded apical end of daughter tubes that preserve black peridermal material is confluent with the external surface of black peridermal material of the parent tube ( Fig. 5A View Fig 1, A 2 View Fig ). Nowhere on the parent tube is there any evidence of isolated basal attachment discs such as those exhibited by fossils bearing epibiontic specimens of Sphenothallus ( Fig. 6 View Fig ).